I have a '91 z28 with the 350. Driving w/ the A/C on the car will eventually get up to like 240*+ in this damn Texas Heat. Both fans running all the time, new radiator, new water pump, new hoses, flushed system, new thermostat(180*), good air dam, nothing in between rad. and cond. to block air flow. Runs at good temp w/ A/C off. Don't know what else to do. Know it has good pressure, cuz after shutting car off at 240* it boils over in to the overflow tank. ANY SUGGESTIONS PLEASE!!!

 

What percentage of your temp meter is 240*? If it is only a little more than half I wouldn't worry about it.

 

I had a very similar problem. I changed rad cap,thermostat,put in a high flow waterpump, turned fans on earlier with no fix. It turns out my rad was screwed even though I flushed it. Went to a rad shop and had a custom 3 core copper rad made for $300CDN. Works sweet with only one new problem. Runs too cool! Never gets past 1/4 on the temp gauge no matter how hard shes driven in any temp. Im gonna have to change thermostats again. LOL

 

You really should go in and change the prom settings as well as getting one of those fan switches to turn your secondary fan on at a lower temp. That's what I did and I dont see 200* ever.

 

I just figured out what's making mine run too hot, even though I havent fixed it yet. I found my exhaust manifold to be glowing, caused by retarded timing or a bad injector, etc, and it was heating up the engine compartment big time. I unplugged the injector and ran it around, and though it didnt run very well, obviously, it didnt overheat or anything. So get a digital laser thermometer from radio shack or something and check your exhaust manifolds, or run til really hot and open the hood in a dark garage and pull the hood light. Just a thought - I found my problem by chance lol. Good luck!

 

Well it runs at low temps when A/C is OFF. Only heats up when A/C is on and when accelerating. Doesn't rise when sitting at lights.

 

Man I dont know - get a lower temp fan switch and a prom with lower fan turn on/off temps. Not trying to offend, are you sure your thermostat is facing the right way? I HAVE made this mistake before! Is the A/C working properly? Does it happen if you're sitting in park with A/C on? I'd have guys who know stuff just come look at it - maybe they'll know or see something you dont. Where are you in Texas?