I love hot weather and cooling systems - GTA fun

[poohbah]

Been a while since my last GTA update, as I've been busy chasing cooling problems on the GTV.

Anyway, had my first bit of GTA covfefe this month.

We've had some pretty hot weather here (12 days over 40C) so as a matter of caution I've been keeping an eye on temp and coolant levels.

Two weeks ago (on a +40C day), I checked it just before leaving the office to go home and level was just above MIN but no puddles or leaks I could see, so I topped it up and went home. No dramas, all performed as normal.

But next morning, I checked again and it had dropped below MIN level. Again, couldn't see any leaky hoses or clamps, but this time found some drops gathering on the subframe below the expansion tank (but also near the water pump). Decided then and there not to drive it til I could get it seen to.

Was a week before there was an opening in the workshop, and I had it trucked there.

Of course it turned out to be a leaking water pump rather than just a leaky hose, but luckily I got onto it pretty much immediately.

So that obviously meant changing cam belt as well as the pump, though I wasn't really too fussed - would have been due in 6 months anyway (last done July 2019). In fact it was probably lucky for me that the pump started leaking when it did - mechanic showed me the belt, and it was just showing some signs of initial cracking.

But a couple of interesting things - when I took it in, I asked them to check the fans were coming on when they are meant to, mainly because the GTA behaves differently to my prior 2.5V6. That would sit steady on 90C almost all the time and the fan would come on when the temp gauge read just over vertical (maybe 92-93C). In the GTA, the gauge generally fluctuates quite a bit either side of vertical depending on traffic conditions, gusto and ambient temperature - with the fan coming on when gauge reads over 95C and turns off just above 90C.

Workshop confirmed fan would come on at 97C and turn off at 92C and said that was normal. I've done some reading on Alfa BB and various forums and seen comments that the temp gauges on the early and middle age 156s and 147s were more indicative of actual temp change, whereas later cars had a gauge that smoothed things out by registering 90C while temp remained between 85-95C. No idea if its true - sounds like an Alfa sort of thing though. And doesn't really explain gauge in my old V6 - that was a '99 car!

But the mechanic did discover only one fan was coming on - the connection on one had worked its way loose/off. Which was an easy fix.

But I do have a question - my fans don't stay running when I switch off (if they were on when I switched off obviously). Aren't they meant to stay on for a bit if the temp is above the shut-off point?

[poohbah]

forgot to note, they also changed the thermostat when they did the pump etc.

[Citroënbender]

Does eLearn discuss the fan strategy? It's a different beast but the 147 fan goes off with the ignition, they (engineers) obviously think thermosiphoning is sufficient to cool the stopped motor.

[poohbah]

I don't have eLearn. I'll ask the guys in the workshop later this week. The annoying thing is that I can't really remember if my old V6 had fan overrun. I've got a sneaking feeling it didn't but can't say I ever thought about it before.

[johnl]

It's a different beast but the 147 fan goes off with the ignition, they (engineers) obviously think thermosiphoning is sufficient to cool the stopped motor.

My understanding:

Once an engine has stopped running, it isn't going to be getting any hotter than it already is...

The temperature of coolant in the engine water jacket will increase after shutdown, as heat soak from the hotter metal continues (until the metal and coolant temperatures equalise).

Thermosiphoning will continue to lazily circulate coolant. This doesn't necessarily mean that a lot of cooling will actually be happening, with almost zero air flow through the radiator core...

Regards,
John.

[Colin Edwards]

Not much point to running a fan if the water pump is stationary.  The fan will only cool the water in the radiator.  Won't have much impact on the coolant around the temperature sensor.  Just draining the battery for very little return.

[Citroënbender]

Just for PB's edification:

http://4cardata.info/elearn/116/2/2000080/2000014/2002065/3234496

...The fans therefore only come on when the ignition is switched ON.

156 eLearn is available free on the above Russian website; even better it's in English. Ура!

[poohbah]

Cheers fellas. So why do the fans on so many cars now continue running after switch off?

[Citroënbender]

Modern cooling systems are more highly stressed and oil specs of greater stringency; this particularly relates to turbo engines.

I respectfully think @johnl doesn't give thermosiphoning quite enough credit in conjunction with the natural heat rejection ability of a healthy radiator. That, in concert with cooling fans on either a timeout or temperature threshold, is going to make a measurable difference including effective service life of the oil.

[poohbah]

Interesting.

And thanks for the link CB. I  have tried a similar one in the past (think it was for all fiat group) and was Romanian or similar. But I got scared off by multiple "dodgy website" warnings.

[GTVeloce]

Perhaps some of the newer cars are running an electric water pump hence the fan could deliver meaningful work after engine shutdown?

[johnl]

I respectfully think @johnl doesn't give thermosiphoning quite enough credit in conjunction with the natural heat rejection ability of a healthy radiator. That, in concert with cooling fans on either a timeout or temperature threshold, is going to make a measurable difference including effective service life of the oil.

CB,
I'm really struggling to see any benefit re "effective service life of the oil" from running the cooling fan for a fairly short while after the engine has stopped running...

I agree insofar as thermosiphon effect will occur because coolant in the radiator core will always lose temperature more rapidly than coolant inside the water jacket, and the rate of flow will be somewhat faster if the fans are blowing air through the core, for the obvious reason.

But, I just don't think it usually matters. If it did, then all cooling systems would run the fans for a while after engine shut down, and most don't.

Maybe, if a particular engine design tends to run borderline hot spots inside the head casting (the metal adjacent to the combustion chambers and exhaust ports, by far the hottest parts of the engine castings and where boiling usually would first commence). If so, then normal operating coolant flow might prevent issues with minor localised boiling, but, after the coolant pump stops running the rate of coolant flow will reduce dramatically, and so the now more slowly moving coolant languidly passing by the hottest parts of the head casting might become hot enough to locally and briefly boil...

In such a case, running the cooling fan for a while after shut down might be just enough to produce a thermosiphon effect just strong enough to keep flow rate high enough that there are no strange bubbling noises coming from under the bonnet after parking the car...?

Regards,
John.

[Beatle]

Cheers fellas. So why do the fans on so many cars now continue running after switch off?

My understanding is that this is for the aircon system, not the engine cooling system.  Helps reduce heat soak and system overpressurisation.

In fact I recall on my first Alfetta the aircon, not the coolant fan would 'run on' after use in hot weather.  I assume it was on a pressure switch, not a timer.

[bazzbazz]

Cheers fellas. So why do the fans on so many cars now continue running after switch off?

Many cars have an additional auxiliary electric water pump that continues to cycle coolant while the fans run after switch off.

[johnl]

Many cars have an additional auxiliary electric water pump that continues to cycle coolant while the fans run after switch off.

Do we know what this extra complexity, increased battery drain, and added cost is supposed to accomplish?

I've never actually come across an auxilliary elecric coolant pump, but then I never have anything to do with newer cars...

Regards,
John.