Yo, Recentley my car has started overheating, first i thought head gaskets, but i have noticed that the fans dont kick in when the temp is at half way. Although the fans still work when the air con is on and the temp gauge sits where it should..

How do i fix it and what will an auto elec charge if its not an easy job to do myself??

check to see if the plug on the fans is in correclery and your relay might be shot

Check the relay.
Check the plug.
Check the fuse.
Test the trigger.

Or - take to an auto elec, depending on what it is, could walk out for $100 or less.

check to see if the plug on the fans is in correclery and your relay might be shot

Mine does this all the time the plug is a bit sh*tty, try that.......

A thermo fan is controlled by the ECU, via a 30amp relay.

12v from the main EFI relay is supplied to the fan when the car is on, and then the negative side of the fan wiring runs to the relay and then to earth.

The relay is fed 12v from the main EFI relay to one side of the coil, and the other side of the coil goes to the ECU.

The fan and relay coil both have 12v supplied to them and when the ECU wants the fan to run, it grounds the other side of the relay coil, which pulls the contacts together and switches on the fan. The same thing happens for both fans but they run indipendant of each other.

This is the same way an ECU controls an injector, fuel pump, idle control etc etc. It switches the negative side of the circuit.

The ECU turns the fan on when the engine temp gets to 80 degrees. Once on, the fan will not turn off till the engine temp gets to 78 degrees. This is to stop "chattering" of the fan operation if the temp is tetering on 79.9998. It is also called a hysteresis.



So, if you are handy with a multimeter, you should be able to work out the problem using logic. You say both fans turn on when you turn the AC on. This proves that both work, and are being supplied the 12v from the main EFI relay. Instead of the ECU using the thermo relay to turn it on, its using the AC relay which is wired to turn both fans on. Relay perhaps.

The thermo should have 2 wires going to it. Positive and negative. When the car is running and the fan off, both will have 12v. If they don't, you have a problem. If you unplug the thermo, the positive side will have 12v and the negative will have 0v.

If you are keen to give it a shot I can talk you through it.

An auto electrician should be able to nut the problem out within 20 minutes and replace the relay/fuse/broken connectiong for next to nothing.

lemmi know :)

just took it into the auto elec, they dont even know what the problem is!!

lol

Usually they are pretty good and quick to find the problem.