ENGINE OVERHEATING


Q:

My engine overheats every time I drive it. I can’t seem to get to the bottom of the problem. What goes on with the cooling system?


A:

I feel your pain.


Overheating has been a problem since the beginning of automotive history, but with persistence can always be solved.


The car was designed to run cool originally, so something must be wrong with yours or it would run cool as it did when new. Somewhere, it is not transferring heat away from the engine efficiently.


The engine creates heat, especially in the upper cylinder area where combustion occurs, and transfers that heat to the coolant flowing in the water jacket nearby. The water pump moves the hot water through passages to the radiator, where it is exposed to the flow of ambient air. That air is cooler than the water, so the heat is transferred away from the water, preparing the water for another journey through the engine.


In addition to the cooling system, heat is removed from the engine by two other primary means: the exhaust system, and by radiating it directly out of the engine assembly.


Somehow, your car is not exchanging the heat from the combustion chambers to the outside air. About one third of the heat is removed through the exhaust system. Check to be sure it is not obstructed. It should have straight through “Off Road” type mufflers which remove exhaust pressure and heat better than oval mufflers.


The “heat riser valve”, or “manifold heat control valve”, located at the outlet of the right hand exhaust manifold, is also very important to the overall heat removal of the exhaust system. It must be free to operate and open freely when the engine warms up and exhaust flow increases. I have seen these valves stuck in the off or closed position many times, and I have seen them when they seem to be working properly, but inside where you cannot see, the valve is stuck closed causing excessive blockage of the exhaust gasses. This, of course, impedes the flow of heat away from the engine as well as causing other serious engine problems.


Your Corvette has a dual point distributor without a vacuum advance mechanism. Initial timing is important to engine heat management, so be sure to adjust your ignition timing correctly to avoid heating problems caused by late, or very early initial timing settings. The timing mark on your harmonic balancer ring may have moved away from its original location. If you think that could have possibly happened, be sure to check it. You need to be able to rely on your basic timing settings, and in order to do that; the timing mark must be in the proper location on the wheel.


You mention that the “v fan” is new, and has been checked. I guess you mean the Viscous Drive Fan Clutch assembly. That is very important on your car as it will not stay cool at idle without the help of the fan clutch sensing the increasing temperature of the air coming through the radiator, and then locking up the internal clutch to drive the fan blades and move more air through the radiator core at that time. I should mention that the fan blade is designed to go on the engine in one direction only. It can be installed backwards, which will decrease its efficiency, so be sure it has been installed correctly.


You mention that you have a new radiator. You don’t say if it is an original equipment type aluminum radiator or if you used a copper/brass replacement type radiator. You should know that the use of a copper/brass radiator will decrease the efficiency of your cooling system substantially, and could be the cause of your problem.


Side seals were used along the vertical sides of the radiator on the 1962 Corvette with the high performance 340 HP engine. These seals consist of two vertically installed rubber flaps that fit along the two sides of the radiator, sealing it to the radiator support. Check to see if those seals and the three bottom rubber seals are present. All Corvettes had the three horizontal bottom seals. The seals help to force the incoming air through the radiator instead of allowing it to pass around the sides and bottom of the radiator. Remember, we must exchange heat from the water in the radiator to the air passing by in order to cool the engine. We want to return cool water to the engine so it is ready to absorb more heat.


The purpose of the shroud is to make the fan operate more efficiently. The shroud is placed around the fan blade, at a strategic location in relation to the blade, so as to make the operation of the fan more efficient when the car is idling at rest. Check to see that the fan blade is turning just forward of the narrowest part of the shroud. This is where it is most efficient.


You mention that you have installed two water pumps. I can probably assume that you have covered that potential problem. I was going to mention that I have recently diagnosed an over heating problem successfully when I found a water pump with a slipping impeller inside. Here was an example of a water pump that was turning properly through the belt and pulley on the outside, but was not transferring the mechanical motion to the impeller inside. The slipping impeller wouldn’t pump the water, so the heat stayed in the engine.


The v belt must be the proper size so as to wedge into the v shape of the pulley with good traction. If the belt is not the correct size and shape, or if it isn’t adjusted correctly, it could slip in the groove and not provide enough mechanical motion to the pulley. Make sure the belt and the pulleys are properly mated to one another so the drive force from the crankshaft is properly transmitted to the water pump pulley.


You should know that the lower radiator hose has a spring inside for a very good reason. Just as you would collapse a drinking straw if you were to suck too hard while trying to drink a thick milkshake, the lower radiator hose has a spring inside to keep the hose from collapsing when the water pump pulls water through it. Check to be sure that the lower hose has that spring inside. By the way, the upper hose should not have a spring inside because it needs to collapse in case one of the valves inside the radiator cap fails and does not allow air to return to the inside of the overflow tank when the engine is cooling off after being operated. This is a safety precaution to protect the radiator tanks from collapse in the event of this rare occurrence. 


Speaking if the radiator cap, it does several important things. None of those are more important that maintaining the correct pressure on the cooling system during operation. The correct pressure cap for your Corvette should maintain 13 pounds per square inch when at operating temperature. This is important to keep the coolant from boiling, which would cause a loss of liquid. A loss of liquid would be the fastest way to cause an engine to over heat. Make sure that your cap is the correct type and in perfect condition.


You mentioned that the thermostat has been changed several times. Be certain that is installed right side up. The heat-sensing button must be installed down, inside the manifold, not the other way around. I would use a 180 degree thermostat as it would help transfer heat a little more efficiently than the cooler one.


Do not overfill the overflow tank. Only fill it one half full when cold. You must leave room for expansion, which is considerable, of you will have coolant spilling every time you operate the engine, especially just after you shut it off.


You mention that the engine runs cooler with the heater on. That is quite understandable because you are removing extra engine heat whenever the heater is on. It would seem that you are therefore not removing quite enough heat through your main radiator when the heater is turned off.


If you have a new radiator, you should have enough capacity to remove all the engine heat. Could it be that you installed a new radiator on an engine with enough rust particles still trapped inside the engine to migrate into your new radiator and plug up some of the tubes? This would explain why, even with a new radiator, the heat exchange is not adequate. You may have to remove the radiator and have it checked for proper flow volume.


I would recommend that you use coolant consisting of ethylene glycol and water at about a 50/50 mix. This gives good protection against rust and corrosion, and provides good heat transfer for your 1962 car.


There is quite a lot of information here. I think I have covered most of the issues related to over heating. It takes time to go over all of these things, but the problem can be resolved as you eliminate the possibilities, one by one.