Engine Coolant Fans: Temperatures to turn on [Archive] - GrandAmGT.com Forum

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Mike Jung
09-10-2008, 10:31 PM
The PCM commands Low Speed Fans ON under the following conditions:

The engine coolant temperature exceeds approximately 106C (223F).
The A/C refrigerant pressure exceeds 1310 kPa (190 psi).
The vehicle is shut off when the engine coolant temperature is greater than 140C (284F) and system voltage is more than 12 volts. The fans will stay ON for approximately 3 minutes.


The PCM commands High Speed Fans on under the following conditions:

The engine coolant temperature reaches 110C (230F).
The A/C refrigerant pressure exceeds 1655 kPa (240 psi).
When certain DTCs set.
Why did GM have it programmed to let the engine coolant temperatures get so high ?
Emissions ?

Surely, it can't be good for your engine's fluids ?

Note: The stock (3400 V6 engine) thermostat is 195F/90C.


Mark from MP Racing had my PCM tuned for...
Low Speed Fans commands:
ON: 212F/100C
OFF: 207F/97C

High Speed Fans commands:
ON: 221F/105C
OFF: 216F/102C

So much better driving in traffic jams.

Thanks, Mark :)

ryanbgb22
09-10-2008, 10:56 PM
I only had my fans turn on once, and that was when my car was 5 notches past the 200 and started over heating. Seems stupid to me.

PhantomLover007
09-10-2008, 11:09 PM
I still haven't gotten used to the sound of the fans staying on after the engine is shut off... lol

It lets me know that Mark sold me a qualiy product...

God why do I have the sudden urge to watch Tommy Boy.... lol

hass
09-12-2008, 02:00 PM
i'm running a DHP PCM, and the low speed fans turn on right around 185ish. I forget the exact number.
But they are always running w/ 180 Tstat.

No idea when the high speed turns on.


But I didn't know the car shuts off automatically when it exceeds that certain temp.
That's pretty nifty.

AaronGTR
09-12-2008, 10:19 PM
They probably only want the low speed fans to turn on for regular cooling to keep down the noise and the load on the alternator. The high speed fans are only supposed to be to keep the engine from overheating if you have a problem or are operating in unusually hot conditions. I know they turn them on at different temps when the A/C is on compared to off because of the extra heat added in front of the radiator from the A/C condenser and the extra load on the cooling system. They aren't really concerned with forcing the engine to run at a cooler temp for performance purposes, and yes they typically run at a hotter temp than older engines for emissions purposes.

Mike Jung
10-01-2008, 11:20 AM
The PCM commands Low Speed Fans ON under the following conditions:
...
The vehicle is shut off when the engine coolant temperature is greater than 140C (284F) and system voltage is more than 12 volts. The fans will stay ON for approximately 3 minutes....
...But I didn't know the car shuts off automatically when it exceeds that certain temp.
That's pretty nifty.
No, they mean the low speed fans will stay on for 3-minutes after turning off your engine, if it hits 140C/284F.

gagt Mechanic
10-02-2008, 11:26 PM
they keep on running after the car is shut off because it is over heating. have you ever been driving and stop some were for a few min. you get back in your car and it is hotter than when you shut it off. your coolant still trys to absorb heat from you block and heads even when the car is off. so they continue to run the fans to try and cool it down and not melt anything.

Mike Jung
10-02-2008, 11:52 PM
they keep on running after the car is shut off because it is over heating. have you ever been driving and stop some were for a few min. you get back in your car and it is hotter than when you shut it off. your coolant still trys to absorb heat from you block and heads even when the car is off. so they continue to run the fans to try and cool it down and not melt anything.
Or in the case of MP Racing PCM Tune or DHP PCM Tune:

The engine coolant fans stay on because we/they had them programmed to.

Mine is set to stay on at low speed after key off at 185F/85C (or above) for 30-seconds.