Temp. Gauge seems to be 30 degrees cooler than true temp, What send signal to cooling fans to turn on and off?

Question

I have a 99 Montana, 3.4L V-6, The van ran hot one faithful day, My temp gauge starting surging between 165 to 240 degrees, After checking all the obvious things i found the head gasket had a leak,

Well I have resurfaced the heads, Put on headset gaskets, Replaced the following: temp sensor, 195 thermastat, sepantine belt, radiator, rad. cap, Pretty much everthing, Van is up and running but the gauge operating temp is now at 170 degrees, if i let it idle it goes to 210 before the fans turn on.

I ran a tempature gauge to the bottom of the radiator and found the actual temp was 195 degrees. inside reads 170

What can be giving me the faulty reading? I went ahead and replaced the sensor and superstat again even though the other ones were new, same results, Van is running good no problems with leaks and gauge is not floating around, it just doesn't seem to be reading the correct tempature, which concerns me that the fan won't turn on at the real 210 but 240 degrees

got any ideas

Answer 1

Factory gauges usually aren't accurate.

If it's really bothering you, you can wire an aftermarket fan control to your fans.

http://www.jegs.com/i/Flex-a-lite/400/31...

Have them turn on and off on whatever temperature you want.

Answer 2

The fans don't turn on until the computer sees a temp of about 225 then the fans turn on.

My wife drives a 2000 Olds minivan with the same engine and it also runs about the same temps you describing. Her gage is a little above half way when the fans turn on high which is normal as far as the manufacturers are concerned.

The temp senser is located in the intake manifold before the t stat and that's why the temp is so high.

I don't think you have anything to worry about. I hope that helps.

Answer 3

uhhh...auto: trans fluid runs through bottom rad too! you shoot temp at bottom hose!its not a false signal. its giving u the temp of the block from the temp sensor. you're checking temp at the bottom of the radiatior! the whole purpose of a radiator is to cool down hotter coolant. its like checking the temp of the exhaust and comparing that to your gauge. the temp its running at now is perfect: doen't get any better than that. think your worring a little to much...if you really want to know hook a scanner up with live data. check what the temp the comp has and compare it with your gauge.

Right, but i fix cars and im tryin to help ya. 210-230 is normal for gm. 240 is too hot. regardless what your rad is saying the temp is being read by your temp sensor in the intake. and youll be payin for more repairs for bein' hard headed. good luck. and i didnt see water pump in your replaced everything list. and if its an auto you could have been checking trans fluid temp: but what do i know? u got the answer u wanted. ;0)

best way to know is hook a scanner to it and compare gauge reading with temp sensor temp. imean think about it...you had the heads machined....the vehicle will never run exactly the same unless you purchase new heads...they've been machined...still with in specs...but machined. u know? its running at a good temp.