Really weird cooling issues and fan control E38

[bignick]

sent this to BP automotive tullierfansettings.jpg. I'm curently loss.





i apologize in advance. ive only got use of one arm right now, so there may be typos...


ive got your harness, your fan harness, 2 lt1 fans with brand new ac delco motors. brand new 2011 camaro water pump, brand new cu730 big block 454 c30 radiator and a ac delco 15lb cap. heater core hoses are ran from water pump to heater core, nothing in between. steam vent is t'd into the heater core return (just like a factory TBSS)

1978 c10 with a 2011 3500 Express van L96 and 6L90e E38 PCM. Van came stock with a clutch fan. Had to get local tuner to segment swap a silverado fan control into my PCM.
all brand new ac delco sensors
here's my problem:

truck is kicking both fans on low at 195, problem with this, thermostat isnt opened up yet. so engine continues to heat up, gets up to 221 on driver side head sensor, this kicks the fans on high. and this causes the fan to cool the coolant in the radiator to 131F and the thermostat never opens and engine gets hotter....

only way i figured out what was happening was i got a temp gun and started reading every spot.

i also purchased hp tuners to help with the issue. im still learning it.

so what ive done is opened the scanner, I can manually turn the fans off, let the engine get up to temp, about 212 and this will eventually heat up the coolant in the radiator and then open the thermostat. i can then let the temp sensor get to 226 (gm low fan turn on) and I can turn both fans on low with fan 1 on command. temps will drop to 219 (gm low fan cut off) or I can let the low fans run and get to 205-208. I can repeat this process over and over, and never need the high speed.

Now lets just say I do kick fan 1 and fan 2 circuits on to turn both fans on high, this will over cool the radiator, close the thermostat and get the head sensor back up to 221 all with the fans staying on the whole time..

i have gone through hp tuners, trying to set the fan temps higher and the fans are not commanding themselves to turn off at the selected temperature I have programmed...

im getting loss as none of this is making sense. i dont know if the a/c switch is over riding the fans? I will attach a screen shot of my settings. I know youve told me before that y'all can program these to work correctly. Let me know if you can provide some assistance. Truck goes on the dyno in the morning and im trying to figure this out.

[bignick]

tullierfansettings.jpg

no idea why this is so small

[BMWMD82]

I am not an expert on discrete fan settings, though there is some good info here if you search. That said, your situation makes no sense to me. The thermostat should open when the engine gets to the proper temperature, regardless of radiator temperature. That is the whole idea of a thermostat, really. You will have the same problem (probably worse) driving down the freeway at 80 mph in cool weather. It should run right where the thermostat wants in that type of situation; it definitely should not overheat.

[gtstorey]

I've seen post on different forums that on some GM cooling system designs that if changes in the coolant paths (such as plugging passages for heater core instead of looping) are made then the warm water in the block doesn't get to the thermostat to get it to open, or at least not open a soon as they should. I never really figured out how true this is, but sounds like might cause your problem.

[bignick]

We ended up figuring it out before coming back to this post. You hit the nail on the head. We bypassed the heater core and looped the water pump inlet and outlet to the heater core with the “u” shaped hose…sub 200f temps now! I had flushed the h/c forwards and backwards 2xs. Had me fooled!