Very occasional S54 coolant overheating on track

[PCarroll]

I have a highly developed 2005 M3 track car that has a very strange history of overhearing. The car is working very hard. But it has plenty of cooling capacity. I am stumped.

Over the years it has had a better tune, an alpha-n tune, and now is running the CSL software with cams. But the overheating problem has persisted throughout. It also has a larger PWR rad, larger oil cooler, etc. The engine fan is removed and replaced with electric. But on the track this is irrelevant.

The strange thing is that the overheating is very occasional and very immediate. The car has lots of cooling capacity and I have replaced the water pump and the thermostat several times. And the problem has spanned engines. The key symptom is that it only overheats occasionally.

e.g. I just got back from a 3 day lapping weekend at Mosport. The car ran fine for 2.5 of the 3 days. But part way though a session after lunch on Sunday, the needle immediately went to the red. It ran in the middle of the gauge for the entire rest of the weekend! And when it moved, it moved fast!

I also have an AiM SoloDL logger on it and this confirms the problem. According to AiM, the coolant temp went from 88C to 112C in less than 1km!

Engine oil temp in this car usually runs up to 120C but was only 109C at the time of the overheat. All readings are from the stock sensors. Ambient was only 23C (73F). Saturday was hotter but I did not have the problem.

I was thinking of installing the oil thermostat diverter to help. But I don't think that's addressing the actual problem.

All I can think of is a sticking thermostat. But if it was open for most of the weekend, how could it close mid session? Plus I have had I think 3 thermostats in there.

Really looking for ideas here. Any ideas are appreciated.

Peter

[bimmerboy318]

I’m no expert, but have you ruled out a bad temp sender? What do you do after it “overheats”? Pit in and let cool... then go back out and all is fine again?

[jayjaya29]

Maybe install something like this, for a second temp sensor:

https://www.racegerman.com/product-p...sender-adapter

[eacmen]

Concur. Check the temp sensor. You can also log engine inlet and outlet temps via INPA to see if they agree. I think AIM only gets engine outlet from the canbus.


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[aeronaut]

"...the coolant temp went from 88C to 112C in less than 1km!"

Wow!
Like above, sensor?
Also, air pocket in system? Although hard to understand how either of those would span engines (unless you re-used the sensor)?

[ScotcH]

Classic symptom of the temp sensor getting air/steam ... in our case, it was from either a head lift and introducing combustion gasses, or bad plumbing for our electric water pump. Once we fixed the routing, never had an issue again. You are running an OE style water pump? Why are you running a thermostat at all? On track it's pointless.

Especially since the oil temp is not climbing, I would not suspect an actual overheat ... it's either the sensor, air on the sensor, or steam. Unless just that portion of the water is getting hot (ie, no flow ... as with your suspected thermostat)

Second the suggestion to put in another sensor, and maybe even a coolant pressure sensor, just to eliminate that issue. We had ours on the line that feed the water pump form the overflow tank.

As a data point, our e36 s54 runs pretty hot at around 95-105 all the time ... but seems to be happy there. I'd kill to see 88C

[Haifisch M3]

any pressure in the cooling system after fully cooled down...next morning?

[PCarroll]

Sensor eh? That's easy to try... It's possible it was reused from the old engine. When it increases, it increases slowly as if it is the water. i.e. not a square waveform as I would expect from a sensor or wiring. See below.

Once it overheats, according to AiM, the oil temp does start to climb as well. But not at the same rate as the water. But it does start to move.

To me it seems as if the thermostat just shut. I can't think of anything else that would make it go up that fast.

After letting it cool in the paddock, there was no pressure in the system and the coolant level was a bit over full. But it was not cold cold yet.

[Haifisch M3]

Yup stuck thermostat has happened to me before although I was always told the get stuck in open position...not always