Hi guys I have a strange one here, I have a 96 TE MAGNA, and I have noticed that when the car is idleing and at normal operating temp, when the car has the aircon off, it will start to overheat and the temp goes up. But for some strange reason if I leave the aircon running the car will not overheat. Can anyone think of why this would be happening? You would think it would be the other way round but its got me baffled as to why its happening.....

Thats an easy one - your main engine fan has died. When you put the AC on, the second fan kicks in and reestablishes airflow.

Could be temp switch on the radiator, or the fan itself.

Your a legend mate thanks, just one more thing, if its the fan thats died, am i right in thinking the fan wont spin? Also if it is that, what would i be buying to replace it?

Be careful or you'll need a new engine soon.

Okay this is important! Turn the AC on & open the bonnet, using AC will force both fans to switch on, now if only one working then your main one died. IF both are working then the problem is most likely your sending unit at the bottom of the radiator which activates the fan when water temperature goes up. Also your car is not lpg by any chance? i had similar problem but in my case it was lpg related.

I had a similar problem on my TJ, I checked the fans operation as per above (Andrei1984) and the fans did work but it seemed like it was on low speed. Then I checked my relays to see if the mid and high modes work and they did so next I ended up changing the cheapest parts like Coolant temperature sensor (mine in next to the thermo switch on top of the engine) and the problems diappeared.

Hi A* , was wondering what your lpg related issue is, Mine is LPG and I have this problem.
Cheers
Steve

Lpg needs hot water to vaporize the gas, my lpg computer was malfunctioning thus preventing fans from turning on thinking water was too cold, when in fact it was not, what lpg system u got?

Your a legend mate thanks, just one more thing, if its the fan thats died, am i right in thinking the fan wont spin? Also if it is that, what would i be buying to replace it?
A dead fan will just sit there not spinning. My TS V6 when bought had both fans dead. A quick trip to the wreckers fixed that.