Ive got a 95 z28 lt1. The temp gauge reads about 194 when just cruising around 65 70. If I get on it and get the rpms up then the temp goes down to about 185 untill i get off of it. I have allready changed thermostat, so i flushed the radiator out and allot of crap was coming out. so after everything the car is still doing the same thing. I also noticed that the hose going to the thermostat housing doesnt feel pressurized and is quite cool compared to the return hose. So could it be the radiator is that clogged? Before you ask yes both fans are working , i have them on constant right now till i get this figured out.

 

Make sure the radiator has no obstructions. I'd suggest a backflow be done. I'd also make sure the drive belt was in good shape, with the proper amount of tension. Next, I'd pressurize the cooling system with a hand held tester to 15psi and watch for any signs of a leakdown. It should hold the pressure for a while, and be adequate. I'd then start looking at the water pump. Inspect the bearings, check for any play (remove the pulley and look at the hub, check for any movement directly in and out. If there's any, it's no good). Also, turn the hub slowly and listen for any scraping, dragging, or otherwise snags. Be sure you're not burning any by checking the smell of the exhaust. It would smell sweet and would have a white tinted smoke. The last thing I would personally do, since it's the most time consuming, would be to check the thermostat itself. Drain the coolant and visually inspect the thermostat for any reason it would be stuck open. My honest opinion is the water pump. Based on the symptoms you provided, It sounds like that during low RPMs, the engine is getting a subpar amount of water, but when you give it a little more, the water pump is spinning faster, throwing more water throughout the system. Just my $0.02. Hope any of this novel helps!

 

My car doesnt have a drive belt to the waterpump ive got a mechanical pump mounted right on the front of the engine.

 

You could still have a bad pump, but not likely. A new stock radiator is less than $200, and will definitely work better than than the old one. Make sure the air dam at the front of the car is still there and that there is not a pile of trash in front of the radiator

 

Ok thanks Pete, gonna buy a radiator this week and see if it makes a difference. will let ya know. I'm pretty sure its the radiator cause you cant see the coolant circulating in there and for some reason when the engine is cold and i take the cap off ,turn the engine on it overflows quick. i dunno i'll try replacing it first.