1918-1936 Cooling System Problems & Cures

By Stephen Kassis

Early Chevrolet engines, both four and six cylinder, are subject to overheating problems. Some problems have an easy fix and others can be very involved and expensive to correct. If you are experiencing overheating problems, do not run the engine or you risk serious damage to the engine and especially to the cylinder head.

A common problem that is really not a heating issue is overfilling the radiator with coolant. Early radiators are not pressurized. They have an overflow tube to allow excess water to flow out to the ground. If you overfill the radiator, heat from the engine will expand the water, forcing it up and out of the overflow tube. This may not indicate an overheating issue! Check your temperature gauge before assuming that your engine has overheated. Fill your radiator until the coolant or water just covers the tubes in the upper tank. This will allow for expansion and prevent overflow.

There are many things that can cause engine overheating problems. Engines from 1936 and earlier have water pumps with packing nuts. If the packing nut is too loose, air can get sucked into the cooling system, causing cavitation. When this happens, air bubbles prevent the water pump impeller from pushing water through the system. The overheating that results from this problem is easily remedied. Check the packing nut to make sure that threads are showing. Add packing if the nut is turned in all the way in the housing. Snug down on the packing nut with a water pump wrench and turn the grease cup in until resistance is met. If the water pump bushings are in good condition, this should solve the problem. If the bushings are worn, this will only help temporarily and rebuilding or replacement will be necessary.

A related problem can occur on 1926-1935 engines. These water pumps have a baffle plate behind the water pump impeller. This plate was steel in 1926-1929 engines. In 1930 it was changed to a brass plate. This baffle plate is vital to good water circulation. It must be in good condition or overheating problems can occur. Pull out the water pump and check the baffle plate to make sure it is not rusted through or missing. A new baffle plate should be installed if there is any damage to the existing one. On 1926-1928 engines the baffle plate is attached to the back of the water pump housing. In 1929-1935 models, the baffle plate is pressed into an opening in the block, directly behind the water pump.

Regular maintenance of these early bushing type water pumps is mandatory to prevent problems. The bushing that resides under the pulley needs to have a few drops of oil EVERY time the vehicle is driven any distance. In addition, about every 100 miles, the grease cup needs to be turned in to grease the shaft.

With the baffle plate removed from the engine, it is a good opportunity to check for a more serious problem – rust and corrosion buildup in the water jacket area. In 1929-1935 engines the baffle plate is covering a large opening in the water jacket. The early engines are prone to having rust flaking off and blocking water flow. In severe cases, the water flow will be slowed until overheating occurs. Two possible tests for this problem are to remove the water pump and baffle plate. Check for rust flakes with the water pump removed. If necessary, remove the water pump baffle plate on 1929-35 engines by driving a screwdriver or punch through the left or right side of the baffle plate. Do not do this in the center of the plate as #1 cylinder is directly behind the plate. Large deposits of rust flakes and corrosion here will indicate heavy rust in the water jackets.

The fix for corrosion in the water jackets is a very involved one. The best way to solve this problem is to remove the engine from the car and place it on an engine stand. However, before going through that exercise, do a little more investigation. First, remove the cylinder head and the soft plugs. Visually check for corrosion and use a magnetic retriever to see how much corrosion has built up. If warranted, drain all fluids and remove the engine, mounting it on an engine stand.

Rotate the engine upside down on the engine stand. Take the engine outside and use a high pressure water nozzle. Force the high pressure water into all the water jacket openings and watch the rust come rushing out. For large flakes of rust it may be necessary to use needle nose pliers to break the flakes to remove them. You will be amazed at how much cooler the engine will run with this restriction removed from the water jacket area.  This procedure should also be followed whenever you rebuild an engine.

Early engines were not designed to have modern anti-freeze used in them. Until 1933, most engines did not have a thermostat. If anti-freeze is used in systems without a thermostat, it can foam and push out of the radiator cap, just as if the vehicle were overheated. We recommend using plain water with a water pump lubricant to keep corrosion in check. These are non-pressure cooling systems and anti-freeze was designed to work on pressurized systems with thermostats. If you are in a cold climate and are concerned about freezing, add anti-freeze at the end of the driving season (when freezing is a danger) and drain it out in the spring.

We have developed a new type of water pump for 1929-1934 cars & trucks (except Standard) with sealed bearings instead of bushings. This totally new water pump eliminates the problem of foaming anti freeze. It also eliminates maintenance – no grease or oil is required. With this water pump, anti freeze can be used without fear of foaming. The new water pump looks exactly like an original except that it does not require lubrication because of the sealed bearings. It has also been designed with a full width impeller to move the maximum amount of water through the system. It is a great upgrade for the early six cylinder engines.

Overheating can be caused by a bad head gasket or a cracked cylinder head. To check for this possibility, do a compression check on each cylinder. Pull out all of the spark plugs and inspect them for rust. If rust is found on the plugs, it will indicate water in the combustion chamber. With the compression gauge in place, crank over the engine several times and log the reading. You should have readings that differ no more than 10 pounds between all cylinders. Low pressure in two adjoining cylinders will indicate a possible blown head gasket. Low pressure in other than adjoining cylinders can indicate a cracked cylinder head, cracked cylinder wall or burned valves. In any case, the head should be removed for inspection and repairs.

Distributor timing can cause overheating. Be sure to check the timing if your engine is overheating.

The radiator is a likely problem area when overheating is involved. Early Chevrolet cars & trucks used honeycomb radiator cores until 1933. The original honeycomb design core cannot be cleaned out as it has a zig-zag design where the water flows. Another thing to consider is that the radiator is around 90 years old. Over the life of the radiator the metal in the core will lose its ability to transfer heat and will become less and less efficient. A new radiator may be required. A flow test can be done but it will not be a definite indicator of a good radiator. The best test for a radiator is to check all of the other items that can cause overheating. When you have eliminated all other possibilities, it will probably be time to replace the core.