Engine Coolant Over-Temp after hard braking

[MinDseTz]

At a track day at ECR, I expected heat to be an issue, but not in the way it presented... Everything seemed hot but fine.

When braking (1G+) after a long straight, I would see the coolant temp jump and throw an alert. After coasting around at 50% for a few corners, it would jump back down like 40 degrees.. There was no steady rise or drop. I'm not sure if this is due to polling, oil starvation or something else?

Is the coolant temp directly measured or is it implied through cylinder head temp?

Any insight or diagnostic suggestions would be appreciated.

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[Ewheels]

Are you reading coolant temp or cylinder head temp? There is no digital readout for coolant temp (unless digital display cars are different). The coolant temp needle is basically useless, it'll read dead center all the time unless you're actually overheating. CHT is accurate. Engine oil temp is inferred via CHT, time running, RMP, ambient temp, ect.

There shouldn't be random spikes in coolant temp from braking so something is not right here. Is your coolant full? You could check for air pockets as well. After that, I would think software gremlins might be at play here

 

[MinDseTz]

Are you reading coolant temp or cylinder head temp? There is no digital readout for coolant temp (unless digital display cars are different). The coolant temp needle is basically useless, it'll read dead center all the time unless you're actually overheating. CHT is accurate. Engine oil temp is inferred via CHT, time running, RMP, ambient temp, ect.

There shouldn't be random spikes in coolant temp from braking so something is not right here. Is your coolant full? You could check for air pockets as well. After that, I would think software gremlins might be at play here

CHT and ECT (I corrected this because I initially wrote EOT) are displayed. The alert was coolant over-temp but I pulled the DCTs and it was all 3 over-temp. I was told the heat soak causes it after long straights and it was normal. I’m gonna add a bunch of cooling for next time and I’m going to send in my oil just in case.

I’m going to data log next event too because I think it’s just lag. I’ve seen lag with afr and lambda on my data logs so it might just be that.

*edit* Also, yeah the coolant was full, and I didn't check for air pockets. It wasn't random enough for me to think it was air pockets, but can lots of sloshing around under cornering and braking cause that? Is ECT and EOT inferred?

 

[Ewheels]

CHT and ECT (I corrected this because I initially wrote EOT) are displayed. The alert was coolant over-temp but I pulled the DCTs and it was all 3 over-temp. I was told the heat soak causes it after long straights and it was normal. I’m gonna add a bunch of cooling for next time and I’m going to send in my oil just in case.

I’m going to data log next event too because I think it’s just lag. I’ve seen lag with afr and lambda on my data logs so it might just be that.

*edit* Also, yeah the coolant was full, and I didn't check for air pockets. It wasn't random enough for me to think it was air pockets, but can lots of sloshing around under cornering and braking cause that? Is ECT and EOT inferred?

CHT is a direct reading. EOT is inferred. Not sure about ECT as my car doesn't have that reading.

I'm still thinking it's a weird software blip because hard braking should not make coolant temps spike. None of the temps should ever really spike, they should gradually climb. Something else is going on here.

 

[EFI]

Not sure about ECT as my car doesn't have that reading.

ECT is a PID in a scanning tool, not displayed in the dash.

Either way, ECT is not a direct measurement and should not be used (much like EOT).

There's absolutely no reason why your CHT (which is the only thing you should be monitoring) would go up 40* during braking and then back down almost immediately after. Even if your waterpump was bad or something it would still take alot longer than a few seconds (especially when you're 100% of the throttle) for it to go up 40*. When you're braking, the engine is in DFCO which shuts off the injectors completely. There's no heat going into the engine during that time.

Something is up with your sensor or the ECT calculation.

 

[MinDseTz]

ECT is a PID in a scanning tool, not displayed in the dash.

Either way, ECT is not a direct measurement and should not be used (much like EOT).

There's absolutely no reason why your CHT (which is the only thing you should be monitoring) would go up 40* during braking and then back down almost immediately after. Even if your waterpump was bad or something it would still take alot longer than a few seconds (especially when you're 100% of the throttle) for it to go up 40*. When you're braking, the engine is in DFCO which shuts off the injectors completely. There's no heat going into the engine during that time.

Something is up with your sensor or the ECT calculation.

Maybe I'm wrong but I was focusing on multiple things. I do remember seeing the CHT temp jump from what looked like 320 (red) to something like 280 on the digital dash gauges. The drop looked significant and it wasn't gradual. I'm assuming there was lag because wouldn't a sensor issue cause noticeable fluctuations?

 

[Norm Peterson]

Sounds more like a sensor or a less than positive connection issue somewhere.


Norm

 

[EFI]

Maybe I'm wrong but I was focusing on multiple things. I do remember seeing the CHT temp jump from what looked like 320 (red) to something like 280 on the digital dash gauges. The drop looked significant and it wasn't gradual. I'm assuming there was lag because wouldn't a sensor issue cause noticeable fluctuations?

You shouldn't really be at 280* either, that's insane. And frankly the car would have gone in limp mode before getting to that point. The PCM limits the engine RPM to 3000 if CHT gets past 270*, it's quite literally the last stage of prevention.

320* CHT is melting pistons and valves.

CHT won't go from 280* to 320* while decelerating in a matter of seconds unless the engine is literally on fire.

Either you saw something else that wasn't there (which is fair while you're racing and concentrating on a million different things) or the sensor is not functioning correctly.

 

[ZPD]

Maybe I'm wrong but I was focusing on multiple things. I do remember seeing the CHT temp jump from what looked like 320 (red) to something like 280 on the digital dash gauges. The drop looked significant and it wasn't gradual. I'm assuming there was lag because wouldn't a sensor issue cause noticeable fluctuations?

280* 320*???? I think that I went into limp mode when I hit ~265 a few months ago on the track.

 

[MinDseTz]

280* 320*???? I think that I went into limp mode when I hit ~265 a few months ago on the track.

I swear I read somewhere the threshold for CHT was 270-300 or something. Did your trans overheat and cause it to go into limp mode?

 

[ZPD]

I swear I read somewhere the threshold for CHT was 270-300 or something. Did your trans overheat and cause it to go into limp mode?

no, I can't remember the exact message but it was obvious that it was the cylinder head overheating. I went into limp mode, slowed down significantly, and went back to the pits. After letting it cool down I went back to the track and if I got above ~250 I started short shifting until I got down to ~235. It wasn't a fun game and stressful to drive, hit the apex, braking points etc while keeping one eye on my digital gauge.

 

[MinDseTz]

no, I can't remember the exact message but it was obvious that it was the cylinder head overheating. I went into limp mode, slowed down significantly, and went back to the pits. After letting it cool down I went back to the track and if I got above ~250 I started short shifting until I got down to ~235. It wasn't a fun game and stressful to drive, hit the apex, braking points etc while keeping one eye on my digital gauge.

edit*

So here are the temps at which "limp" kicks in. I can't find CHT limit, so I'm assuming it doesn't have one. The inferred temps are more conservative anyway, but CHT would likely be a little higher than EOT.

Also TOT is trans oil.

Also I'll add 269 is threshold for rear diff, and dropping below 249 is subsequently required to drop the "hot" flag.

 

[EFI]

So here are the temps at which "limp" kicks in. I can't find CHT limit, so I'm assuming it doesn't have one. The inferred temps are more conservative anyway, but CHT would likely be a little higher than EOT.

CHT is about 10-12* higher than ECT, which is why I mentioned ~270* that it goes into the final protective mode.
'
EOT will always be higher than CHT on track where it can't be regulated by the coolant.

 

[Ewheels]

Random fun fact: for those of you typing "*" for the degrees symbol, if you hold "alt" and type "248" using the number pad, it'll put an actual degrees symbol like this °

 

[EFI]

Random fun fact: for those of you typing "*" for the degrees symbol, if you hold "alt" and type "248" using the number pad, it'll put an actual degrees symbol like this °

Fun fact...if you to go google images search and type in "middle finger gif" then copy and paste in here it will display our reaction to the * vs °

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