More On Vapor Lock

Posted by TxGoat On 2023/6/19 12:52:38

My '37 120 is prone to mild vapor lock and fuel boiling in the glass filter bowl near the carburetor.

It lacks the fuel pump heat shield, which probably contributes to the problem.

The temperature gauge indicates 175 to 185 F under most operating conditions.

The car does not boil the coolant.

After running the car for a few dozen miles in 90F + temperature, I stopped and left the engine running and used a point& shoot temperature sensor to check on things.

The head temperature showed to be 180 to 185 front to back. The radiator upper tank showed 175 to 180 and the water inlet pipe showed 155 to 160 F.

However, the crankcase area, where the fuel pump is mounted, showed 200 to 205 F.

I think the pump is picking up too much heat from the crankcase to work effectively with the fuel sold today.


Intsalling the heat shield would probably help, especially at low speeds in hot weather, but I doubt if it would entirely eliminate the tendency.

200 F is well within the normal range for crankcase temperatures.


Adding extra gaskets to the fuel pump mounting would probably help, but that would reduce the pump stroke, which would not help. The fuel line from pump to carburetor showed to be around 150 F.