Bob's Studebaker Resource Website

by Jim Wood - Avanti Owner

....response to a question about an overheating engine

I play an ASE Master Mechanic at work so I can help you play one at home. You don't tell us anything about what you have done so I will start at the beginning.

What type of an overheating problem is it? Does it force coolant out of the radiator? If so it could be exhaust gases getting into the coolant from a leaking head gasket, etc.

We are dealing with a car that is 30 years old, are you sure that the gauge is reading correctly? You can use a thermometer placed in the radiator fins near the upper hose to get a good reading, even better if you have an infrared thermometer you can use it.

You say the timing has been set correctly; your engine should use the big cap GM distributor. I have seen many problems with these distributors, remove the cap and rotor and look for rust around the weight pivots. The weights can wear into the pivots and jam into place causing full advance at all time. Attach a pump to the vacuum advance and make sure it moves.

You should have an overflow bottle; this is used to keep air out of the engines cooling system. The way it works is you fill the radiator all the way up, as the coolant heats up it expands and the radiator cap allows expanding coolant to go into the bottle. After you shut down the engine it cools and a vacuum is created in the radiator and the radiator cap opens and the coolant in the bottle returns to the radiator. Several things can go wrong with an old overflow system that can cause it not to work. Remove the radiator cap and make sure that BOTH seals are in place, there is a seal on the bottom and a seal under the lip. The seal under the lip of the cap is used for the overflow system, if you don't have the seal the system won't work. Have the radiator cap pressure checked to make sure it is operating correctly. There is a small diameter hose running from the radiator neck to the overflow tank, you can't have any leaks in the hose or at the clamps. Also make sure that there is a hose going from the overflow cap to the bottom of the tank, I have seen these fall off.

Make sure the fan belt is tight, with the engine OFF take your thumb and place it on the alternator fan and try to turn the alternator. If the fan turns and the belt doesn't the belt is loose.

Do you have a shroud? If it's missing this would cause overheating.

Is your fan clutch working? With the engine cold and OFF spin the fan, the fan clutch should allow it to spin freely. Run the engine to operating temperature, SHUT the engine off and spin the fan, it should be harder to turn if the clutch is working correctly. The clutch helps the engine heat up faster and saves gas by disconnecting the fan when you don't need it.

Do you have the correct thermostat for your year of engine? Later model cars run hotter thermostats. The temperature is stamped on the thermostat.

If the radiator cap is old replace it, especially if you can't test it. You have a 30 year old car, the radiator could be plugged. With the engine cold remove the radiator cap and look down the neck, do you see a lot of deposits around the cooling tubes? The radiator tubes may be plugged up, you can use a thermometer or an infrared thermometer to check these tubes. Run the engine to operating temperature, if the radiator is a top to bottom flow the temperature should be about the same at the top of all the tubes, cooler but the same at the middle of all the tubes, cooler yet but the same across the bottom of all the tubes if not you may have a plugged radiator tube. Works the same way for a cross-flow radiator, hottest on the side with the upper hose, then cooler in the middle and coolest on the side with the lower hose.

Are the radiator hoses in good shape and the clamps tight? If the hoses are hard they should be replaced, and if they are too soft that they can collapse. I have also found hoses that separate inside allowing a flap to block coolant flow.

Is the coolant rusty? If a proper mixture of anti-freeze hasn't been used in the past I have seen a deposit of rust cover the inside of the coolant passages in the block and cause poor heat transfer. I have also seen this cause the impellers on the water pump to rust away causing a lack of coolant flow in the engine.

Good luck,

Jim Wood, Jan 2011 (fleetcare2 on AOAI Forum)