1918-1936 Cooling System Problems & Cures
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.
There are many things that can cause an engine to overheat. 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. When this happens, the water pump impeller cannot push water through the system. The overheating that results from this problem is easily remedied. Snug down on the packing nut and turn the grease cup in until resistance is met. If the water pump bushings are in good condition, this should solve the problem.
A related problem can occur on 1926-1936 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. The baffle plate is vital to good water circulation. It must be in good condition or overheating 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.
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.
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. Remove the cylinder head, water pump and the soft plugs. 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.
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. 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.
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 or burned valves. In either case, the head should be removed for 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 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 75+ 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.