View Full Version : coolant fans run all the time

02-19-2008, 02:06 PM
Hi all,
Checked and topped up coolant last week for 1st time, (2001 V6) then noticed temp gauge not reading and heater doesnt seem very warm and coolant fans run even when the engine is cold.

After researching here it seems the temp gauge doesnt display true temp but why is mine reading zero and why are both coolant fans running? are the two issues related? Where is the temp sensor?


02-19-2008, 04:13 PM
does the heat come out hot?

when you "topped off the coolant"... why did you do that? does it leak?

i would confirm that the gauge is working, if it is, you have 2 bad switches or relays.. highly unlikely.

02-19-2008, 04:30 PM
you might also have a leak somewhere. check your recovery tank and your rad, both when hot and when cold. not the rad while hot of course, itll spill everywhere. could be its just got enough coolant to show, but not enough to cool. try filling everything to where it belongs, then let it run and idle for a while, checking underneath to see any leaks.

02-20-2008, 09:31 AM
I'm pretty sure i dont have a leak, the only reason i checked is that its really cold here at the moment and i had to leave my car out one night, i've owned it since the summer and (shame on me) have never checked it before.

Well, the level in the rad was low, i couldnt see the coolant so i topped it up to the top, checked again a couple of days later and had to add a little more, since then its been stable; the level now is about 1" below the top when its cool then once i start the motor it comes up to the top. I dont see any evidence of any leaks, everything looks dry, there are no drops on the garage floor etc.

The heater does blow warm air but not as hot as it should be.

How do i check the gauge? and what brings the fan on, if its the same temp sensor as the gauge could it be a bad sensor? where is the sensor located?

I'm going to change the thermostat today as i think its either opening too early or is partially stuck open causing the heater not to get hot enough, especially with the coolant fans running all the time.

Thanks guys for all your help!!


02-20-2008, 02:01 PM
Just replaced the stat, heater got toasty warm, fans ran at 1st the cut out as it got a little warmer, i think the same time the temperature gauge started working again, new stat opened, vented the air out and all appears to be working again normally.

Wierd though how all this happened because of a bad thermostat, still cant quite figure it out.


Dave D
02-20-2008, 04:33 PM
Hey Pete, I am having a similar problem. The car is a 98 Formula, but the fans won't kick on. My uncle said at his shop he can manually turn them on. Water pump was just changed. Anyway what makes the fans kick on? Uncle thought they were turned on by PCM. I had the car tuned after headers, etc. Help!

02-21-2008, 08:47 AM
Dave, i understand the fans are turned on by the PCM, i searched 'cooling fan' here and found numerous posts about adjusting the cut in temp especially on modded engines.
My guess is it senses the coolant temp from the same sensor as the instrument temp gauge. I think in my situation the stuck thermostat was somehow causing the sensor to read incorrectly which in turn messed up my gauge and the cooling fan operation.

There are others here with far greater knowledge than me who will hopefully set you straight but changing the thermostat is a 10 minute job and costs about $6, there was practically no coolant loss, definitely worth doing if you are at all suspicious of its operation, dont forget to replace the gasket at the same time.

Good Luck


03-03-2008, 07:16 PM
I have a question about this. Does the pcm need to see a signal from the Coolant temp sensor or can I unplug it and plug my spal fan controller into that sensor and not throw a code. I have a aftermarket coolant temp guage in my RX7 and dont use the sensor to turn fans on or for the guage. I just want to plug my spal fan controller right into the sensor and not have to put another one somewhere else.

Dave D
03-11-2008, 06:35 PM
Pete- all is good now. I had another programmer plug HPTuner up to it, and he found the problem. We had changed everything including the plug connecting the sensor. The program had set the low side ot come on at 235 and the high to come on at 240. Wayyy too hot. I heard that a few 98s have jumped the settings after tuning them. It was orig set much lower!!! Fixed now- he pulled tune and reset temps.