So the engine was overdue for an oil change. I hadn't been too concerned since not all the oil in there was past due date, due to topping up over time, and the car never does short journeys (where the oil doesn't reach full temerature for long enough or at all, the worst thing for oil longevity). A significant quantity, maybe half, was 'fresher' than it would be if the engine didn't use oil (like my old Accord, or our Saab, which will do 15,000km with virtually no lowering of the oil level). So some days ago guilt, and a vague feeling of impending doom prompted me to do something about this, and I've changed the oil.
Anyway, the old oil was 10w/40 (Penrite 'full synthetic'), with the top ups being 20w/60. Despite the topping up with thicker oil, when I drained the old oil (hot) it seemed very thin and runny. New oil is Penrite 20w/60 mineral oil, though I didn't have enough needing to top up with about another litre (the total amount needed was nearer 5 litres than the quoted 4.4 litres). The 1 litre needed to top up was what I had on hand, i.e. Penrite 10w/40 'full synthetic' (what I use in the Saab), so the oil fill will be a bit less than the full thickness of the 20w/60, but still fairly viscous as engine oil goes.
The immediate result was a total lack of variator rattle on start ups, and the engine is now generally quieter and feels smoother than it was (I suspect a lessening of 'piston slap'). The second thing I noticed was that the engine now feels significantly more powerful at lower rpm. However, it now seems somewhat less 'willing' to rev so freely as before, and feels to have a bit less power at higher rpm. This might possibly be due to feeling more powerful at lower rpm rather than an actual decrease in higher rpm power...
The third thing, fuel economy has improved markedly. Previously it was consistantly sitting on 8.4L/100km (displayed), but after a 'reset' (from cold) it fell to 7.9L/100km with my usual driving pattern. I did some highway driving yesterday (about 100km give or take), mixed in with some urban driving, and the readout is currently at 7.2L/100km. This is way better than it has ever been, i.e. previously it would take a great care and a featherweight foot (or a very long run on the highway) to achieve a readout near to or below 8L/100km (and then only barely below it). Now it's easy to get below 8L/100km.
My speculation re the apparent change in power characteristics is that the thicker oil has improved ring seal, and increased oil drag, simultaneously. This (increase in power) is more apparent at lower rpm because at lower rpm there is more time for compressed gasses to leak past the rings (on each compression and power stroke), so conversely if the rings are leaky there may be significantly less compression at lower rpm resulting in a power loss. At higher rpm there is less time for gasses to leak past the less than perfect rings, so with leaky rings there may be less power loss at higher rpm. However, with thicker oil there is more oil drag, so at higher rpm you may not gain much extra power from better better ring seal, but you may lose significant power from oil drag...?
Better ring seal giving better compression should have an affect on economy. Another thing that might occur with poorly sealing rings is a lessening of oil burning, resulting in reduced or eliminated detonation (in cylinder oil contamination of the inducted air / fuel can result in detonation). The ECU should detect this (if it is occurring with leaky rings), and pull back the ignition timing, which would result in power loss and worsened economy...
Regards,
John.
I'm not 100% sure on the science behind heavy and light weight engine oils and how it effects the running of an engine, but I too can speak from personal experience.
I used to run Castrol magnatec 10w-40 in my 164, to which I noticed it would burn a fair bit of oil every few thousand kms or so. The last oil change I switched to full synthetic penrite hpr-15 15w-60.
Immediately I noticed a drastic reduction in 'lifter tick' and a much more smooth running engine. I haven't noticed any power gains/losses but the oil consumption has pretty much halved.
Goes to show that oil really does matter and can play a big part in the engines reliability and durability.
Andrew.
Mine feels slower when there are reds and blues behind it! :P
Overall though, I also reckon it's the Placido Effect.
I had a similar experience too recently with my 147 twin spark, i've been using 5w-40 for about a year, i moved back to 10w-50 in the last oil change and consumption has dropped and the variator noise on start up is gone. Fuel consumption seems to be the same - i've travelled about 1000km since the change, next change i might go to 10-60 to see how that goes.
A litre of oil for every tank full of fuel?
Crikey.
Quote from: sportiva on July 18, 2018, 03:31:06 PM
The placebo effect
My car always performs better after I polish it
My car also performs slightly better when it's clean...
But, this improved performance and economy with new and thicker oil is definitely not placebo, the effects are too substantial to be mistaken...
Regards,
John.
Quote from: poohbah on July 18, 2018, 10:55:36 PM
A litre of oil for every tank full of fuel?
Crikey.
My thought too...
Regards,
John.
Quote from: V AR 164 on July 18, 2018, 01:49:51 PM
I'm not 100% sure on the science behind heavy and light weight engine oils and how it effects the running of an engine, but I too can speak from personal experience.
Accepted wisdom is that the thinner the oil the better the fuel economy. This is due to reduced 'pumping losses', i.e. thinner oil requires less energy to pump it through the system. With pumped oil, and more so the thicker it is, this is energy parasitically lost and so not available at the crank. This means that with thicker oil a somewhat greater throttle opening is needed to make X power at the crank, whatever is needed to overcome rolling resistance and push the car through the air. Which of course means some degree of lessened performance and increased fuel consumption.
However, this assumes that the rings are in very good condition and need no thicker oil than is required to adequately lubricate them. If the rings aren't all that great and tend to leak a bit, then thicker oil helps improve the sealing performance, so improving compression, so improving power at Y throttle opening, i.e. a lesser throttle opening will be needed to produce the X crank power needed to propel the car. A smaller throttle opening equates to lessened fuel consumption, potentially despite the increased pumping losses associated with the thicker oil.
Regards,
John.
"Powered by Penrite" :D
Isn't that what Ferrari got pinged for doing deliberately earlier this F1 season?
Related question for the guru's here, appreciate any thoughts.
I'm just about to box up a twin spark CF3 engine which had a dubious history before it came into my hands. It's now clear that the cylinder head was repaired after a cam belt failure, however the previous owner neglected to inspect/replace the big end bearings. The engine had just begun to wipe the #2 BE when I inherited it. Now ready for reassembly, after a crank grind, rod re-sizing, new rings/hone etc, I'm torn as to whether I should drill some oil drain holes in the oil control ring grooves. The flimsy 2mm solid lower rings must surely be overwhelmed trying to scrape the bore clean of thrown oil. Not a hard mod to do, and I think is low on the risk scale for a road car, I'm just wondering if it will mitigate the chance of the dreadful oil consumption I hear of.
Has anyone else contemplated or done this mod?
Thanks in advance
Vne
How will you possibly make it worse? :)
The evolution of CF3 pistons in Eper is interesting reading, the last iteration in V84 (change note D7995) refers to "cava", implied respective to the rings grooves...
Quote from: Vne165 on July 19, 2018, 08:47:54 PM
Related question for the guru's here, appreciate any thoughts.
I'm just about to box up a twin spark CF3 engine which had a dubious history before it came into my hands. It's now clear that the cylinder head was repaired after a cam belt failure, however the previous owner neglected to inspect/replace the big end bearings. The engine had just begun to wipe the #2 BE when I inherited it. Now ready for reassembly, after a crank grind, rod re-sizing, new rings/hone etc, I'm torn as to whether I should drill some oil drain holes in the oil control ring grooves. The flimsy 2mm solid lower rings must surely be overwhelmed trying to scrape the bore clean of thrown oil. Not a hard mod to do, and I think is low on the risk scale for a road car, I'm just wondering if it will mitigate the chance of the dreadful oil consumption I hear of.
Has anyone else contemplated or done this mod?
Thanks in advance
Vne
After the rebuild you have described if you use 10w60 full synthetic you should have no oil usage issues.
Sportiva - I must be lucky, my JTS just needs a minor top off every month or so.
Quote from: Vne165 on July 19, 2018, 08:47:54 PM
I'm torn as to whether I should drill some oil drain holes in the oil control ring grooves. The flimsy 2mm solid lower rings must surely be overwhelmed trying to scrape the bore clean of thrown oil. Not a hard mod to do, and I think is low on the risk scale for a road car, I'm just wondering if it will mitigate the chance of the dreadful oil consumption I hear of.
Has anyone else contemplated or done this mod?
Thanks in advance
Vne
Never drilled pistons, but FWIW I recall David Vizard writing in his famous seminal work 'Tuning the BMC A Series Engine' that it is beneficial and doesn't appreciably weaken the piston.
Apparently some BMC pistons had no holes under the oil control rings, and some had long slots (the worst ones also had a long tangential slot that started under the oil ring and extended at an angle all the way down to the bottom edge of the skirt...). The slotted pistons were very weak and so not suited to high rpm work, since the top of the piston had a tendency to separate from the skirt. The 'solid' pistons were much more robust since there was no slot to act as a stress riser, but suffered from some oil related issue the details of which I can't recall (probably failure to 'scrape' enough oil from the bore, resulting in the compression rings lifting off the bore on a too thick oil film). Drilling several small holes behind the oil ring apparently eliminated or at least reduced this issue, without causing piston failure.
I would imagine that you don't want to drill such holes too close together, for fear of weakening the upper part of the skirt. From memory the holes were drilled in the ring groove through to the inside of the piston on the thrust faces, not on the sides of the piston. I would take care to ensure that the edges of the drilled holes were carefully chamfered (i.e. remove the sharp edge around each end of the drilled hole). When I built a semi competition A series engine (in another lifetime) I used forged Mahle racing pistons, which from memory had such holes from the factory.
Drilling such holes should have no significant affect on relative piston weights. The amount of metal removed is minimal, and will be similar from piston to piston. When 'balancing' a set of pistons it's amazing how much metal can be needed to be removed from the heavier ones to equal the weight of the lightest, one gram of aluminium equates to a surprising quantity of metal.
This (weight difference piston to piston) might apply more to cast pistons than forged ones, and modern production tolerances likely mean less difference between pistons than in the good ol days.
Regards,
John.
Citroënbender - Very interesting. Is it possible to obtain a copy of the change note somewhere, or is it simply just a notation in ePer?
Baz - Yes have purchased Penrite 10W-60 Synth already.
JohnL - Thanks, some food for thought there. I cut my teeth on A Series engines as a kid many years ago, so do remember those pistons you describe.
So the decision I have then is to spend the time to mount the pistons in the milling machine, drill a total of twenty four holes (three per thrust side/piston, de-burr and clean...). Or just whack em in. Will let you know what I do.
Cheers
Vne
Quote from: Vne165 on July 20, 2018, 09:16:32 AM
JohnL - Thanks, some food for thought there. I cut my teeth on A Series engines as a kid many years ago, so do remember those pistons you describe.
So the decision I have then is to spend the time to mount the pistons in the milling machine, drill a total of twenty four holes (three per thrust side/piston, de-burr and clean...). Or just whack em in. Will let you know what I do.
Cheers
Vne
As I'm sure you know, slots or holes in the oil ring grooves are to allow excess oil to drain to the inside of the skirt, instead of 'filling' the space behind the oil rings. If the space behind the oil ring fills with oil then more oil will get past the oil ring and possibly interfere with the compression ring seal (which are not so good at 'scraping' oil from the bore), and then enter the combustion chamber. These holes (and maybe slots?) are very common, so much that I'd be surprised to not find them in any vaguely modern engine. So, I'm surprised that your pistons don't have them...
Long slots in the skirt are there (which they aren't these days, at least I've not seen such slots for many years) so that the piston can be run with a very tight tolerance to the bore, which eliminates piston slap when the pistons are cold, but not seize when the piston heats up and expands (the slots get squeezed tighter instead of the piston seizing, but which probably still increases piston drag to some degree). This makes for a slightly quieter engine when cold, but at the expense of a substantial reduction in piston strength, which might be OK for a low stressed / low revving engine, but not so much for 'modern' more highly stressed / higher revving engines...
Drilling holes in a piston that doesn't have them already shouldn't require a milling machine, just careful work with a hand held drill, or something like a 'Dremel'. You want to avoid 'nicking' the top or bottom horizontal faces of the ring grooves with the drill bit (especially the upper face). So, I'd use a drill bit with a diameter a bit less than the width of the groove, don't let the drill wobble, keep the bit at 90° to the vertical axis of the piston.
I'd grind some metal from the sides of the drill bit so that the bit diameter is slightly reduced, from the corners of the cutting edges and upward for a few millimetres. If you do this then the edges of the spiral flutes shouldn't contact the piston (if the drill doesn't go in dead straight). Avoid the bit contacting and cutting into the pin bosses.
Regards,
John.
To my knowledge the blocks are the same.
Quote from: sportiva on July 20, 2018, 02:28:27 PM
and what are your thoughts on machining a wider groove in the pistons to allow for a deeper oil control ring
How much metal would remain in the ring land thickness after machining the oil ring groove wider? I suspect that might be the limiting factor (?).
Looking around on the interweb, from what I see it appears that the JTS pistons don't (surprisingly) have any holes in the oil ring grooves, and also use one piece oil rings (also surprising if true). Is this correct?
If so, then I'm not a fan. It's my understanding that one piece oil rings are generally inferior to three piece oil rings. As per my understanding, three piece oil rings are effectively two quite flexible rings separated by a spacer. One piece rings are stiffer, and as a result don't conform to the bore as well as three piece rings do, often permitting excessive oil to get past the ring.
If this were my project I'd be looking to fit three piece oil rings (if possible), and drilling the oil ring grooves.
I've never had my pistons out so I don't know what they look like. Are the TS oil rings similar to the JTS? Do the TS pistons have holes drilled in the grooves?
Regards,
John.
Hi JTS owners
Excessive engine oil consumption with JTS engine. Found an interesting thread on Alfa Owner forum in the UK, in particular the post, dated 15-01-17 on outcome.
http://www.alfaowner.com/Forum/alfa-147-156-andamp-gt/1023626-alfa-romeo-156-jts-oil-mystery.html
With more familiarity with the change in power characteristics (with the thicker oil), I now don't think that the engine has lost top end power. There is a definite increase in low rpm power, it's unmistakably there from idle and into middling rpm. This is especially noticable when moving off from rest with almost no need to carefully balance clutch and throttle movements as before, the car will just move easily without wanting to 'bog down' as the clutch is let out. It's also better able to climb inclines in a taller gear, and more responsive when increasing speed from cruising rpm.
This makes it feel 'as if' it has lost some power in the upper rev range, there is now not as big a change in acceleration as the rpm increases. It's a relative perception thing.
Regards,
John.
What height middle ring? The CF3 TS went from 1.5 to 1.2mm in its first design change note.
Quote from: sportiva on July 21, 2018, 09:08:23 PM
Do you really think that a small change of viscosity will have a noticeable effect moving a 1300KG mass
If the engine is full of old crud/sludge oil that is more akin to Molasses, sure. (Just ask my oldest son, he's an expert on it!)
Quote from: sportiva on July 21, 2018, 09:08:23 PM
Do you really think that a small change of viscosity will have a noticeable effect moving a 1300KG mass
Yes, at least a fairly substantial viscosity change can.
The old oil was quite 'thin', seemingly quite a lot thinner than it was when new even considering that the oil was warm when I drained it, it ran out like black water. It was still thin in the catch tray after it had cooled down. Oil can both thin out or thicken up in use, I've seen both happen with used oil. I've changed oil many times over the years, and seen hot oil run out both thick and thin, this was definitely quite a bit thinner than I would think to be usual.
This page from BITOG:
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/652719/Does_motor_oil_usually_thicken
The new oil is quite thick for an engine oil. I think it's more than a small viscosity change from what was in the engine to what is in there now.
The compression rings rely on the oil film to properly seal the combustion chamber, whether the rings are in perfect condition, or less than perfect. The more worn or glazed the rings and / or the bore suface (or the more resistant the rings are to moving freely in their grooves due to gunky deposits in the ring lands), the more likely it is that the ring seal won't be all that good, and the more the rings will rely on the oil to help seal the chamber. This is why adding some oil into the combustion chamber for a 'wet' compression test will increase compression (telling you whether poor compression is due to bad rings / bore or leaky valves, i.e. the excessive quantity of oil around the rings will 'artificially' and briefly increase ring seal if the rings are poor, being diagnostic of bad rings).
Poor ring seal and the engine loses significant compression on the compression stroke, and loses cylinder pressure on the power stroke (blow-by). Both of these problems can, if bad enough, result in significantly less power being produced. A too thin oil (for the circumstance) will be less able to assist the rings in sealing, it will just get 'blasted' out of the ring / bore interface by the compression and combustion pressures. A thicker oil will (may) stay in place more effectively. If the rings are not perfect then thicker oil will probably help, and result in higher combustion pressures, and more power will be produced.
It is the increase in power due to improved ring seal, especially at lower rpm when there is more time for pressure to be lost on the compression and power strokes, that has the noticable affect on moving the car. It's less likely to have as significant an affect at higher rpm, because there is less time for pressures to be lost via the rings.
Hypothetically and veering way off topic, if it were possible to raise rpm to an impossibly high number then the need for piston rings would largely disappear because there wouldn't be enough time for significant pressure to bypass the piston, a tightish piston to bore clearance would be enough. Turbine engines largely rely on this, i.e. there is a small clearance between the turbine blades and the housing (i.e. no physical seal), but the turbine blades move so fast that the compressed gasses can't escape and are adequately retained within the spaces in which they need to be.
Regards,
John.
Quote from: sportiva on July 22, 2018, 02:59:02 PM
The engine I did the autopsy on shows significant contamination of the piston rings large amounts of thick gunk stuck in and around the rings that would definitely hinder the sealing performance of the rings
If the rings get stuck in the grooves, then they aren't able to push against the bore and of course sealing suffers. I suspect it's not uncommon for a diagnose of 'bad rings' to be made when in reality the rings themselves are OK, just 'glued' into the grooves, and a good cleaning would set all to rights...
Highly detergent oils might help (and maybe the more effective 'engine cleaner' oil additives out there). After changing the oil on my old Accord (first oil change in my ownership) using a highly detergent deisel engine oil, after about a week or so I started to notice an unexpected improvement in engine performance. At the time I speculated that the cleaning action of the oil might have removed gunk from the rings and lands, maybe...
A reasonably objective indicator that the thicker oil is doing something beneficial is the improved fuel consumption (and the improvement may or may not be as much to do with the oil being new as it is to being thicker, not really sure). A few weeks ago the indicated consumption was steady at 8.8L/100km, then it dropped to a steady 8.4L/100km after changing the upstream O2 sensors, now it is hovering between 7.6 and 7.7 L/100km after changing the oil. This is a bigger improvement with new / thicker oil than with new 02 sensors...
Regards,
John.
Quote from: sportiva on July 22, 2018, 05:10:24 PM
can we really afford to experiment with different oil weights or formulations when the oil type is so specific "10-60 SYNTH"
The 10 weight is to protect the camshafts and variator and the 60 is for the bottom end and oil burning. we could move between the oil weights and protect one more than the other. Keep the bottom end safe and sacrifice the top end or use a thinner oil and sacrifice the big end for the cams and variator
So if the 'cold thinness' "is to protect the camshafts and variator" from damage and wear, it's curious that when my old thinned out (quite) oil was changed to a substantially thicker new oil, the obvious variator rattle on cold start up (and sometimes hot) completely disappeared...
This would imply that with thicker oil, less of it might be draining from the internals of the variator after shutting the engine off, even if we assume that it may take a slightly longer for the variator to fully pressurise on start up. Assuming that the variator is being most worn / damaged during the time it is audibly rattling due to lack of oil, surely this would be more protective of the variator than allowing it to rattle away for several seconds with a thinner oil? Or, it might be that the thicker oil also mostly drains out, but whatever residual thicker oil still in there (and this is may well be more than with a thinner oil) acts to more effectively 'cushion' the internal impacts that cause the audible rattling...?
The cams. My understanding (FWIW...) is that it doesn't take much oil to lubricate the cam and tappet faces at start up, when rpm are particularly low. Just enough to keep the surfaces separated is enough, and even when a lot of oil is present most of it gets squeezed out due the considerable pressure that exists between the cam and tappet faces (the most highly loaded surfaces in any four stroke engine). From previous operation a residual oil film will remain clinging to the surfaces, and before start up there will be a significant 'reservoir' of oil at and around the point where the cam lobe is contacting the tappet face. A 'fillet' of oil will be sitting at / around this contact point, held by the clingy nature of the oil and the surface tension of it. At start up, as the cam lobe rotates this oil will be 'wiped' onto the lobe surface, lubricating it until more oil becomes present.
This would I think be more to do with the 'hot' rating of the oil, since most of the drainage would occur while the oil is still hot, so an oil that is thicker when hot (say 60 weight compared to say 40) may well be more protective at cold start up, because more is likely to be present at the cams / tappets at cold start (or at least avoiding not quite enough being present as might conceivably occur with a thinner oil).
All else being equal, the thinner the oil the less this will tend to occur, as thin oil will more readily drain away from the cam / tappet faces after shut down, as opposed to a thicker oil, which will less readily drain away. This residual oil (and more so the more of it) should be adequate to lubricate the cam and tappet surfaces for the first few seconds of start up operation, before oil is pumped at full pressure through the system and finds its' way onto the cams, and more so the thicker the oil may be. So, as I see it, it may well be more likely that a thicker oil will protect the cams / tappets at start up more effectively than a thinner oil. I could be wrong, I'm not a tribologist, but it seems logical if I'm not missing something...
My understanding of the purpose of 'multi weight' oils is simply that such oils thin out (with heat) less than do single weight oils, i.e. all oils thin out with heat, but multi weights less so (and less so the greater the spread between the 'cold' and 'hot' numbers of the oil). This means that a cold multi weight oil (with a low 'cold' number) will circulate more quickly at start up and flow a greater quantity of oil through the system more quickly, getting oil to the bearings rapidly (noting that there will be residual oil in the bearings too, probably more with a thicker oil...), helpful to avoid issues if the engine is used too hard too soon after start up, and perhaps for cold oil to spray onto the bore surfaces more quickly (and again noting that residual oil will cling to the bore walls and in the ring pack as well, probably more so with a thicker oil).
I can't see that using an oil with a cold rating of 20 as opposed to 10 (or even 5) is going to be problematic, 20 is still reasonably thin and will pump through quite quickly from cold, perhaps with the exception of use in
very cold ambient temperatures. Using the thicker oil I've noticed no difference in how long it takes for the CEL to switch off, which is I think a function of the oil pressure coming up to X. It doesn't take more time, and seems to be a bit quicker if anything (totally subjective as this is...).
Still, it's not good for cold oil to be too thick, it places a significant load on the oil pump, and affects fuel economy, at least until the oil warms up. In extremely cold conditions it may just take way too long for the cold thickened oil to thin out enough to pump easily, appreciably longer than it may take for the coolant temperature to reach operating temperature.
Assuming this to be the case, a thinner cold rating could avoid problems if say the driver uses the engine hard once the coolant is up to temperature but the oil is still too cold (or if the driver just uses the engine too hard when nothing is yet up to temperature, as will be the case for some drivers...).
I suspect that the real reasons why FIAT specified an oil with a hot 60 rating (for "decidedly sportive use") might be so that more oil would be present at the cams / tappets at cold start (given stories I hear re cam lobe wear), or, was simply to reduce oil consumption that occurred with these engines when habitually driven fairly hard over time. For 'normal' use they specified a hot 40 rating, which turned out to be too thin to keep oil consumption at a reasonable level, even with gently driven engines. Could this also be related to ameliorating cam lobe wear, I have my suspicions.
As if I haven't blathered on long enough, it occurs to me that we should also keep in mind the difference between the 'cold' and 'hot' numbers in the oil spec. The greater this difference (e.g. 10W60 having a difference of 50, as opposed to say a 20W/60 having 40 difference) the more likely it is that the oil has a heavier dose of 'viscosity improvers' in the formulation. These chemicals are the first things to degrade in an oil, and the more there is / are the more the oil is likely to degrade in X conditions over Y time. This will cause the oil to lose some degree of its' 'multi weight' capability, whether by thinning out when hot or thickening up when cold, or both, I don't know.
All else being equal, two similar oils one with a wide 'spread' and another with a significantly smaller spread, the one with the smaller spread is likely to have less viscosity improving chemicals in it, and therefore more likely to last longer. It's my understanding that fully synthetic oils tend to be less affected by this degradation due to the superior qualities of the base oil, meaning less viscosity improvers tend to be used, but even so the affect still exists because they still have some.
Apologies for the long post...
Regards,
John.
Que? ??? (as said by Manuel)
;) :) :) :)
Quote from: bazzbazz on July 24, 2018, 08:26:03 PM
Que? ??? (as said by Manuel)
Hi Baz,
Que what? Can you not follow my admittedly long winded arguments, or implying that they are incorrect?
I don't mind if anyone disagrees with something I may write, it's always open for discussion.
In this case it was suggested that thin oil is good for the upper engine components but not good for the bottom end components, and conversely that thicker oil is good for the lower end but not good for the upper end. I've never heard this argument before, and can't see why it would be true. I just put forward an argument as to why I think this isn't necessarily so. If my argument is wrong then it would be interesting to be told why...
Regards,
John.
Sportiva - tap tap tap (private joke)
Quote from: sportiva on July 27, 2018, 04:44:55 PM
10-60 SYNTH covers the specific demands these engines require
Agreed, but I'm not convinced that using a 20W/60 will cause any problems, if the engine is used sensibly (i.e. not revving it hard with cold oil).
Such an oil isn't all that much thicker at ambient temperature than a 10W/60. If the engine can cope with the relatively high pumping loads and lesser flow rate of an oil with a 'hot' rating of 60 (quite a thick 'hot' rating) up to maximum rpm with the oil at operating temperature, then I think it should also cope with a somewhat thicker 'cold' rated oil, if the engine isn't revved hard until warmed up.
I agree that a 'synthetic' oil (whatever that may mean with a specific oil, i.e. maybe 'hydrocracked' mineral oil, or better still PAO / ester based) is preferable to a more conventional mineral oil. I chose a mineral oil simply because it was cheaper at a time when funds were depleted (i.e. I was next to broke...). If cost were not an issue I would always use a PAO and / or ester based synthetic oil, but such oils are not inexpensive. I'm confident that a good quality mineral oil will be quite OK so long as it's not left in he engine for an extended oil change interval (I change at 10,000km, though the last change was admittedly a bit late).
I would and do avoid mineral oil in our Saab, as these engines are well known to be
extremely hard on their oil. This is due to the oil passing through the bearings in a turbocharger, the very close proximity of the cat convertor to the sump (heat soak into the oil), and a marginal crankcase ventilation design. These factors conspire to make these engines sludge badly if mineral oils are used, and not changed frequently enough regardless of the oil used (again I change at 10,000km, but would do so more often if the car were used mainly in urban driving, even with a 'fully synthetic' oil, probably at 8000km).
Regards,
John.
I cannot comprehend the disparity in comments by the original poster; in one instance a change of oil (old for new) results in claims of appreciably better performance - yet in another instance - the actual grade of oil used as replacement, the dismissal is effectively "near enough is good enough" with respect to its departure from OEM recommendation.
While I accept that there are indisputably "black arts" (said tongue-in-cheek, the point being some things are such a convergence of miniscule differences that it's effectively impossible to scientifically reduce it all to measures and procedure) the avoidance of hard data in cases such as the above makes them at best entertainment.
Quote from: sportiva on July 30, 2018, 03:20:30 PMIt is not the first few minutes of driving or how gently you rev the engine it is the first few seconds when the engine oil drains back after resting say overnight the initial start the next day is where the most damage is done.
I'm a bit surprised that you think that the difference in cold thickness between a 10w-60 and a 20w-60 oil is so critical. I do agree that all else being equal it is a 'good thing' if the oil can be pumped reasonably quickly at cold start. Penrite also make a 40w-70 engine oil, which could pose a problem on a cold morning (!).
Rpm should still be kept reasonably low with cold oil (even an oil that is relatively quite thin when cold), but that is a somewhat different issue to the initial wear at start up. I still don't buy the notion that the reason to specify a multigrade oil with a low 'cold' rating is that this specifically minimises cam lobe wear, I'm far from convinced that it especially does (more likely the motivating factor might be that it influences average fuel economy downward, assuming an engine with excellent ring seal...).
Oil that is thinner when cold will pump through reasonably quickly, so a 10w-60 fits that bill, and I have no issues with using such an oil in these often oil consuming engines (60 is a bit thick if the engine doesn't consume oil...). However it's my understanding that a 20w-60 isn't hugely thicker when cold than a 10w-60 (if you don't live somewhere like Canada...). Just because 10 is arithmetically only half of 20 doesn't mean that a 20w oil is twice as thick as a 10w, it doesn't work that way (or a 0w rated oil would be infinitely thin...).
At the risk of repeating myself; regardless of the oil used, at cold start the working surfaces are not completely unprotected. There is a residual oil film clinging to them that lubricates 'well enough' until pumped oil arrives at the cam lobes and tappet faces, at best some seconds after start up (possibly significantly longer considering that the oil at the cam lobes isn't pumped there directly). Even an oil that is quite thin when cold takes some time to actually arrive at the cam lobes, significantly longer than the time it takes for the engine to quiet down, but a somewhat thicker oil (within reason) takes only a little bit longer. It's during this time that the residual oil film is important (if it weren't for the residual film then cam lobe wear would be much worse, regardless of the cold oil thickness).
This is mostly to do with the 'hot' thickness. The thicker the 'hot' thickness of a given oil, the more residual oil is likely to be coating the working surfaces at cold start, and to be sitting in 'pools' around the contact points between the lobes and tappet faces due to the surface tension of the oil (less having drained away after hot shut down when the oil is at its' thinnest, thicker equating to less runny). It's this 'pooled' oil that gets wiped onto the lobes as they initially rotate at start up.
You can see these 'pools' of oil if you take a close look at the contact points between the lobes and tappets, most clearly at the moment a camshaft is removed, leaving the oil pool exposed on the tappet faces. It doesn't take much oil to protect the lobes and tappets, but the more residual oil the better, and thicker oil leaves more of it.
This would be more or less the same for say a 10w-60 as for a 20w-60, i.e. it's the '60' that is more important for the residual film. I suspect this might possibly be why thicker oil (when hot) may be more protective of cam lobes etc, i.e. less cam wear during cold starts because the residual film (and associated oil 'pools' between the lobes and tappets) will be somewhat greater, less having drained away. This would be beneficial in an engine prone to cam lobe wear...
So where was I; when I changed the oil I was wanting to use one with a thicker hot rating (more or less as Alfa now recommends). If a 'synthetic' 10w-60 had been available at a reasonable price, then I would likely have purchased it. On the day that I was in town looking to buy a thicker grade oil, the nearest reasonably priced oil that I could find was a 20w-60 mineral oil by Penrite (on a day I was close to being broke...).
IMO a 20w-60 oil will still be fine, it won't cold pump quite as fast as the 10w-60, but it will be quick enough, and there is a residual oil film. Just don't thrash the engine when the oil is still cold (good advice regardless of the oil used), it may not pump easily enough to keep rate of oil flow up to the bearings.
FWIW, I have trouble thinking that an engine that can pump a hot 60w oil (effectively very thick) up to red-line rpm with no problems, would be unable to adequately pump a cold 20w at restricted rpm...
Also FWIW, the SAE cold temperature ratings for oil weights are as follows:
20w from 0°C
15w from -10°C
10w from -20°C
5W from -30°C
0w from below -30°C
My engine is almost never started at sub zero temperatures.
Regards,
John
Quote from: Citroënbender on July 31, 2018, 11:27:57 AM
I cannot comprehend the disparity in comments by the original poster; in one instance a change of oil (old for new) results in claims of appreciably better performance - yet in another instance - the actual grade of oil used as replacement, the dismissal is effectively "near enough is good enough" with respect to its departure from OEM recommendation.
The OEM recommendations are at best erratic. The manual says; "5w-30", "5w-40", "10w-40", and "10w-60". There is a massive difference in the 'hot' ratings, far greater than the difference between a cold 10w and 20w. For "decidedly sportive use" it says to use "10w-60". For "particularly harsh weather conditions" it says to use both "5w-30" (assumed "particularly" cold weather), or, "5w-40" (assumed "particularly" hot weather). I would have assumed that use in very hot ambient conditions and use in a "sportive" manner would both result in quite hot oil, so why the different recommendations?
In the field it also seems that the 30 and 40 recommended hot ratings have been found to be not nearly thick enough to prevent quite excessive oil consumption with many examples of this engine. In response it seems that Alfa retro specified an oil with a particularly high 'hot' thickness rating for all usage (i.e. 10w-60), mostly I assume to reduce oil consumption, but I do wonder if the higher 'hot' thickness rating might have been an attempt to address instances of cam lobe wear as well?
The OE recommendations are all over the place. Treat them as Gospel if you wish, but I've yet to have any issues using oil with a slightly thicker 'cold weight' (i.e. 20w rather than 10w). Were the car used in sub zero temperatures I might well reconsider this...
Quote from: Citroënbender on July 31, 2018, 11:27:57 AM
While I accept that there are indisputably "black arts" (said tongue-in-cheek, the point being some things are such a convergence of miniscule differences that it's effectively impossible to scientifically reduce it all to measures and procedure) the avoidance of hard data in cases such as the above makes them at best entertainment.
I lack quotable "hard data", but, changing from a substantially knackered thinned out old oil to a new thicker oil has resulted in:
1) Significantly improved the engine performance (suggests less than perfect rings)
2) Substantially improved fuel economy (also suggests less than great ring seal)
3) Elimination of variator rattle
4) A generally quieter engine
5) A substantially reduced rate of oil consumption (oil level has not significantly lowered since changing the oil a few weeks ago, maybe 5mm lower now).
I myself find some of this surprising, since I would have expected the thicker oil to allow the variator to rattle for little bit longer considering a somewhat thicker oil will pump somewhat more slowly. But the variator rattle has completely disappeared altogether...
I understand that these are merely "claims", I cannot prove what I'm saying. To me they are as near to 'hard data' as I can expect, as each is a very obvious effect, before oil change and after. If the engine now suffers from accelerated cam lobe wear due to the thicker cold rated oil, feel free to say 'I told you so"...
Regards,
John.
Hi all,
Just following up from post #13, with some details of what I eventually did regards drilling of oil relief holes on my CF3 pistons. Decided to do 6 x 2mm diameter holes in each piston. Worked out well so I hope someone finds it useful and I hope I don't have any oil consumption issues.
This engine sure has surprised me in more ways than one - I may make some other posts just for info - someone else might be mad enough to rebuild one one day too...
Cheers Vne
Pic 1 - Marking out hole locations (6 x piston)
Pic 2 - Drilling in the milling machine
Pic 3 - View of ring lands
Pic 4 - De-burring,,