i have had this problem for quite some time were my car overheats only when the a/c is on. it will start to overheat and i turn off the a/c and it goes back to normal. i checked everything from fluid changed the thermostat a couple of times and nothing still does it. don't know if it's the fan or the relay switch i only have one fan instead of two fans. any previous or current 3rd gen owners have or had this problem. i really miss the cold air my 3rd gen throws out and with this texas heat i need it.

oh forgot to mention it's all stock 305 v8.

 

i could be wrong but i thought they started putting dual fans in them back in the late 80's. the intention was one fan ran at normal cycle and the second fan would kick in after the a/c was turned on and the a/c system reached a certain pressure. thats how it is on my 91 and 92 Z28's. don't know if it's different for the RS's, but i wouldn't imagine it would be.

when you turn the A/C on the radiator (for the A/C) in front of the actual radiator gets hot and adds additional heat to the cooling system. the purpose of the dual fans was to help suck out the extra heat caused by this. if yours doesn't have that i would assume it ran at a higher fan speed when ever it was activated or somewhere the dual fans got removed.

more than likely what is happening/ or happened, is at some point in time the fan was changed out and replaced with a slower motor (cheaper) which is fine for normal duty but can't handle the extra heat of the A/C system, or i've seen issues when people replace their factory radiators with radiators from the car parts chains. even though they say they are for A/C, i've seen alot of cars not work right afterward. could be possible the radiator was changed and can't handle the a/c.

i'm sure some one will correct me if i'm wrong, but those would be my suggestions / thoughts

 

I agree with the above poster!

 

When you say overheat, do you mean into the red zone? Or running at 3/4 of the gauge?

On my stock system, with dual fans, it runs pretty darn hot at this time of the year (100°+ with heat index in the 115 zone). Laredo isn't any cooler than Houston, so I would think that a single fan setup would be testing the system for sure.

Assuming everything is working right, I'd look between the condensor and the radiator. Always surprising HOW MUCH crap gets jammed in there.

A lower amount of antifreeze to water ratio would help. 25% antifreeze and 75% water would do the trick. A bottle of water wetter wouldn't hurt either.

Aside from that, I'd think about swapping to a better higher CFM fan. The stock ones aren't known for their high output. Just about every BMW on the road today has a fan that can be heard over the sound of the engine. Yet I can't hear my fans with the car on at all. And even turning the car off with the hood open, you have to look to see if the fans were on (starting to spin down)

 

Ok I had this same problem. Just fixed it! I tried everything as well.
So started doing some research here and bought the AIRDAM and front plactic piece in front of it. I drove over hr and 1/2> Fixed

 

also try something like a jet swich or hypertech switch to lower the normal temperature. It does make a difference.

 

the fan is supposed to come on when the ac is turned on.is it?

 

it is

 

Thanks for the info. I did notice some 3rd gens do have a double fan and mine only has one.

 

what is the AIRDAM?

 

Airdam came on the car originally forcing more air up to cool the Rad. If you want to find some good info on it do a search on here. My car was over heating for a while. I bought the airdam on ebay looking under camaro 82-92 airdam deflector. Put it on, and my car never ran so cool. And I live in AZ> really hot here. I suggest if you are missing the under cooling pieces, find and buy them. Really makes a difference

 

Here is a link that shows some of the pieces.
https://www.thirdgen.org/forums/body...-plastics.html

 

If your car is not TPI it won't have a dual fan set up, unless the overflow is boiling over the car is not over heating. For instance the gauge on my car is off by 20 degrees.

 

If you have 2 fans, 1 will be commanded by the ECM to come on when the a/c compressor is engaged (it may be once the car has reached a certain temp though...I am not sure). This is mainly to pass air over the condensor to give you cooling at idle or low speeds. I did not think the purpose of that fan was engine cooling, but I may be wrong on that. Either way, idle the car at normal temp, but the a/c on and see if one fan runs. If not, you have an issue to address.

 

Buddy of mine had the same issue of overheating only with a/c on. He only had one fan, so I gave him a spare tpi dual fan assembly i had and he never had another issue. We are both in Texas as well so I hear you on needing the a/c! I have my dual fans on a separate switch and keep them on at all times, seems to work well.

 

My car is a stock 305 TPI