So this is my story:

Earlier today I took my '92 RS (305 TBI) for a 90 miles freeway drive, and the ambient temperature was 96 deg. Since it was so hot and humid, I turned the A/C on. After driving on the freeway around 15 mins, the temp gauge went up to 220. 15 minutes later it went up to 240 (3/4 way). So I turned the A/C off and the temp went down to around 220-230. Average speed was 70 mph, RPM was around 2600 in OD (3.70 rear end).

This is the cooling system setup on the car:
- Stock radiator, dealer installed new in 2001.
- Dual fan setup from 91 Z-28, both fans work fine and wired to turn on (both of them) at 180 deg or if the A/C is on anytime.
- 180 deg thermostat.
- Air dam has a few chips and scratches, but pretty much intact.
- No leaks from the hoses or water pump.

Anyone has this same problem? I know that the easiest solution is to drive w/o the A/C on, but what's the point having A/C if you can't use it on 90+ deg days, right?

I was thinking about replacing the radiator with one that has larger cooling capacity. Since the aftermarket ones are quite expensive, does anyone know if I can install one from a GM truck (say a newer Silverado)? I realize I have to tinker around a bit to mount it, but dimension-wise, will that be possible? The self-servie local junkwayd here has some newer GM trucks that I can take the radiators off.

If you have any other ideas or solution, I want to hear it!

I apologize if a similar topic was posted before....

 

Now I'm going to ask are you sure the fans are working properly? Because something is very wrong with the temps that you stated.

 

Yup.

That's my first thought, so as soon as I got home, I opened the hood and left the engine running (temp still around 220) and both fans were running strong.

However, I would think that at freeway speed the fans won't do much since at that speed, the radiator cooling is pretty much up to the airflow from the front / under the car.

 

How new is your t-stat? might want to check it to make sure it's opening up all the way. Check your water pump as well.

 

1 week old

For leaks?
I don't see any coolant leaking from it or anywhere.
This might be a stupid question, but how many ways can a water pump fails?