I have an 89 IROC weekend car. We've been having a heat wave in So. Cal for what seems like 4 or 5 weeks straight. The car was overheating and I found that the main fan was intermittent. I replaced it and everything was fine until I decided to flush the radiator and add new antifreeze, the coolant was looking a little nasty. It started overheating again (temps were in high 90) I wiggled the fan connector and it stared working again. I also have been trying to get the AC working, I took it to a place and the found the leak in the upper hose. It was working fine on the drive home but once I got off the freeway it began to overheat again and both fans were working.

I have an all aluminum 3 core radiator, both fans are working and the coolant was replaced, although I coolant in the block was never drained.

Any suggestions on what to do now.
Everything works fine when on the freeway with low traffic or on a cool day.

 

Possibly air in the system? Probably already thought of that but with both fans working it shouldn't be overheating unless the waterpump is gettig weak. have you let it get up to temp with the rad cap off and see how the coolant flows. Also check thermostat, could be malfunctioning, I've had one that wouldn't open all the way which caused high temps. Hope you figure it out.

 

Define "overheat".

It's amazing how many "overheating" complaints there are that all that's wrong is, it spews, because it needs a radiator cap; or, people don't know what the "normal" running temp for one of these cars is, and get into some kind of fantasy-land dream about "I want my car to run at 180°"; or, people who think "water boils at 212° so if it's at 210° I better pull over and let it cool down"; or, their particular factory gauge (trim package, not "instrument") moves around more than most others; or various other .... things .... that are NOT overheating.

You're lucky to live in a place where it always stays so cool. For a lot of the rest of the country, ANYTHING in the 90s is a relief from actual heat.

So start there. What it the car ACTUALLY DOING?