2003 ZR2

My ZR2 will idle at temp just fine, but if I run it down the road (with ac on) it starts getting hot and seems worse with faster speed (3/4 gauge). I removed the mechanical fan and installed electric fans, and have also pressure washed the fins of the radiator and condenser. Im not sure what to look at next or why it would idle fine at temp (idled for 45 minutes just under 1/2 gauge) but get hot running down the road. Any suggestions?

 

The only thing I can think of is that your cooling system is marginal and when going faster more heat is being produced. I'd recommend a full system flush before changing any other parts. Check your radiator after you stop the warm engine by putting your hand on it. When my radiator was clogged it was hot on the top and cool on the bottom. Since gunk is heavier than water it tends to settle to the bottom so that's where the clogs are more likely to form. The openings in the radiator are real small so they can get gunked up pretty easily. Since your car doesn't overheat at idle I'll guess that your thermostat is good. As for the fan...it's main purpose is to pull air through the radiator when the car isn't moving so it's no surprise that it didn't solve the problem.

The recommend engine flush is an lengthy process....not just a matter of connecting a garden hose. Do a quick search and you should find it. Besides the radiator some of the water passages can clog up. When I changed my intake manifold gasket the rear passages were almost totally clogged. Although not common your water pump impeller could be going but normally the first thing to go wrong with a water pump is the shaft bearing.

 

Well I got a new water pump and Tstat today for $20 after turning in fan clutch tool. Gonna open the system to replace those (I now the stat sticks a little). While I'm in there I wanna see the condition of the residual fluid.

 

It would be best to verify coolant temp with a scan tool. Compare the Engine Coolant Temperature sensor, (ECT) to the Inlet Air Temperature sensor, (IAT) after the vehicle has set for 8 to 10 hours, (before starting the engine). They should be within 2 degrees of each other. Don't trust the dash temperature gage, they're not known for their accuracy.

Depending on the CFM of the electric fans, and what temperature the sensors are set for, the fans might be causing part, (possibly all) of the problem. At highway speeds, the natural air flow across the radiator is greater than the fans can provide, so they end up restricting air flow if they're on. They should be off, (free wheeling) when you're at highway speeds. That's the beauty of a fan clutch, it only engages when it's needed, otherwise it's free wheeling. Could be your original fan clutch wasn't working properly.

You mentioned that you used a power washer to clean the condenser and radiator fins.... not a good idea.... the force of the water can easily bend the fins. When they get bent, the air flow is restricted. Harbor Freight has a fin straightening tool for $5. The upper radiator hose should be hot at the radiator and the lower hose should be noticeably cooler. If it's not, suspect a restricted radiator.