Engines are designed to run hot for excellent efficiency, but not to the extent that they overheat and damage components by overpressure or loss of coolant. Some say that overheating engines are the typical shortcomings of older cars and anyone who owns one will eventually be left stuck and steaming on the side of the road.
We say that's not necessarily the case. When these older cars came off the assembly line they didn't have an overheating problem, so they obviously have an adequate cooling system (This is mainly true, but many cars during their development were never tested in the summer heat in Arizona or a similar climate, as many are today). It's just that after decades without regular maintenance or a complete overhaul, the car's parts, radiator, engine block, hoses, fans and belts have aged and may not be working as efficiently as they did when new.
If the temperature gauge on your car indicates that the engine is running a bit hotter than usual on short or long trips, don’t wait too long to look into what the car is telling you. It doesn’t mean you need to start tearing apart the car's cooling system, just series of tests and preventative maintenance might be the cure to keeping your classic cool.
Belts and Hoses
Replace any belts that are fraying, have cracks or slipping on water pumps and cooling fans. Do a thorough inspect of all hoses for cracks, swelling and signs of leakage. A good rule of thumb is to check the cars belts and hoses with every oil change and replace them every five years regardless of how many miles you put on the car.
Inspect the front of the radiator for excessive bugs and dirt - these can be removed with any garden hose with a pressure nozzle attached.
Look for any small leaks which would be apparent by the accumulation of white or green deposits anywhere on the tank or the tubes. These can easily repaired by hot or cold welds which we recommend over adding radiator sealants which only eventually compound the problems. The problem with a sealant is that it can impede the flow of water in the radiator core and wear down water pump seals, reducing the efficiency.
If you haven't replaced the radiator cap washer for some time, do so. It's an inexpensive part but essential to proper pressurization of your cooling system.
To check for any blockages that may have developed inside, disconnect the lower hose of the radiator and run water through the top, the water should leave the radiator at the same rate as it enters. If it doesn't, very often just back flushing the radiator can open blocked cooling tubes. On older radiators this process may need to be repeated several times as back flushing can redistribute sediment throughout the radiator and cause huge problems as we found out on our E-Type Jaguar several years ago.
A car's thermostat is what regulates the circulation of coolant through the cars cooling system - it stays in the closed position when the car is cold and opens as it heats up. As the thermostat ages it can fail and remain closed which will cause your car to get very hot...quickly. If your radiator, belts and hoses are in good repair and the car still over heats, replace the thermostat.
The Freeze Plugs
Freeze/Core plugs are usually located on one or both the sides the of the engine block and are designed to protect it from freezing. But over time they can also be an area where water can leak from the cooling system and cause overheating. Worst yet is when they do go, it always at the worst possible time.
Once you find where the freeze/core plugs are located on your particular engine, the tell-tale sign of weeping will be apparent. The ease or difficulty of replacing leaking plugs varies depending on their accessibility.
The Head Gasket
A blown or bad head gasket will cause coolant to leak from your cooling system and you'll find the evidence in your engine's oil or you can find oil in coolant. Either way, it's a mess and the engine will eventually overheat. Frequent checks of your fluids should help catch this problem before serious damage occurs.
Check that heater box, if you have one, for any signs of coolant weeping. Heater cores can easily rust from the inside out and rigging a heater bypass can resolve this problem quickly until you can locate a new heater core.
Check the Timing and Adjust the Carburetor
The carburetor and engine’s timing are not part of the cooling system, but when they aren’t properly adjusted to the manufacturer’s specifications, that can be a likely culprit to your overheating problems.
These simple steps can be difference between keeping you and your classic looking and running cool. Sitting by the side of the road with the bonnet/hood up waiting for a tow truck – definitely not cool!