View Full Version : Water temp/Thermo switch on Rad.

05-23-2009, 10:40 AM
Hey guys,

is this switch supposed to kick start the aux fan when the car is overheating or when the car is at normal operating temp?

I thought that it's when the car is upto normal temperature... and mine isnt kicking in, resulting in some overheating!

Thanks for all the help *th-up*

05-23-2009, 10:46 AM
ok bud first thing s first .lets detemine if its the sensor or the aux fan.pull the three wire plug off the sensor.the brown is ground,with the key on in run,jump across to one of the other wires,a little piece of wire.one side is low speed one side is high speed.If the aux fan works,then we look at the sensor.Mister

if the car has air conditioning,just turning on the air switch should engage aux fan on low speed,key in run position,engine doesnt need to be running.Mister

05-23-2009, 10:58 AM
^Yea I've done all youve mentioned, I just replaced the aux fan, flushed the coolant, bled everything. When the car is hot, all the hoses are hot, so the system is free of air. The thermostat is working because the car is warming up (not stuck open) and the rad is heating up (not stuck closed).

BUT, my question is simple, is the aux fan supposed to turn on every once in a while when the car is upto normal operating temperature? or is that switch just there incase teh car begins to overheat to turn on the fan... Otherwise, I know how to test for it and everything, but if its not supposed to be turning on, then why bother testing...

05-23-2009, 12:02 PM
well there is a low speed side to the switch and a high speed side,so it makes sense it has two temp ranges,probably 92-95 c low temp, low speed, 103-105 c high speed,does the car have air conditioning??? turn the air on,but put heater control in red,no matter ,idling it should not heat up,and the aux fan should be running low speed continous,running down the road at 100 k the thermo switch should tell the aux fan to turn off low speed.know what i mean.its not gonna turn on low speed for overheating issues,its for the air system in my opinion..So i am gonna say it doesnt periodically come on unless air is engaged.Mister

05-23-2009, 12:19 PM
^alright cool, in the bentley manual it says that when the car is in normal operating temperature, the fan should come on. If it doesn't come on, do the whole test that you mentioned up top, and if that works, it means the switch needs to be replaced. I tried that, and the fan comes on when I bridge the wires... otherwise, the car can heat up to almost 3/4 and the fan still doesnt switch on...

and yes I do have a/c, when i turn the a/c on, the fan comes on (low speed).. the a/c being on is also not promoting overheating