Poor Cooling Due To An Obstructed Radiator

The OE radiator works very well when it is clean. Because the air inlet to the radiator is only a few inches above the ground it is common for the radiator to become obstructed by debris.

Radiators that have a small amount of debris on the face may also be obstructed by sand in the fins. The only way to clean the radiator completely is to remove it and back-flush water through the cooling fins. The radiator is at the bottom of the stack of three heat exchangers. The AC condenser is on the top of the stack and is seen when viewing the air inlet from the front of the car. The face of the radiator can be viewed from the right side through the oil cooler hose opening. The air flow reduction is usually twice as bad as it looks from that oblique angle.

   

The radiator works well if it has an opportunity do so. This one had little chance.

This radiator received a coating of oil from a leaky oil cooler hose. Over time the oily area captured dust. One quarter of the radiator was totally obstructed.

The air inlet of the C4 can act a lot like a vacuum cleaner. The leaves are stacked on the AC condenser which is the most forward of the three heat exchangers. In the stack are, the AC condenser, oil cooler and radiator.

Some General Information About ZR-1 Engine Cooling

The cooling system struggles when the ambient temperature is over 95 degrees and the AC is on. If overheating occurs sooner than that it is likely that the radiator is obstructed with debris.
 
The thermostat regulates the engine temperature until the ambient temperature is over about 85 degrees. After that, the thermostat is wide open and it does not matter what the regulation temperature is. With the thermostat wide open the cooling fans and the radiator are limiting the temperature rise.

The DeWitts double row radiator, part number 1139090M, has twice the heat exchange area of the OE radiator and will add about 10 degrees to the maximum ambient temperature limit to about 105 degrees.

I have found that the Spal fan box from DeWitts does not have any advantage over the OE fan box. However, it makes more noise.
 
The temperature sensor readings on the LT5 are 15 degrees higher than the thermostat control temperature. On the LT5 the thermostat is located at the inlet to the engine. So with a 180 degree thermostat the inlet to the water pump is at 180 degrees. Both the analog and digital temperature sensors are located on the injector housing, behind the left water manifold. So, when the thermostat is regulating at 180 degrees, the temperature rise as the coolant passes through the engine adds 15 degrees for 180 + 15 = 195 degrees at the sensors.

The center of the sweep on the analog gauge is about 200 degrees.

When driving on the highway, running the engine at less than 1600 rpm will cause it to run about 15 degrees warmer. This also lugs the engine. Lugging is not good for the bearings. In general, with the OE 3.45 rear gearing, 6th gear should not be used at less than 70 mph.