An unusual gas tank venting system was on 1934 – Early 1936 Chevrolet 1 1/2 ton trucks and 1937 to early 1938 1/2 tons. This was necessary because their under seat gas tanks did not have a fill spout. They were filled directly into the top of the tank. (A few late 1936 Chevrolet low cabs 1 1/2 tons did have a short fill spout which extended through the right side of the seat riser. However, the passenger door needed to be open to reach the filler cap). See tech article titled “1934-36 Chevrolet Gas Tank Changes”. Why General Motors did this is unknown however it surely created a big inconvenience as gasoline could only be added to the tank by raising the passenger side lower seat cushion. On cold or rainy days a passenger would need to stand out of the cab while the station attendant also stood outside to make the fill.
Because air must enter the tank to take the place of gasoline used by the engine, somewhere it must be vented. If there is a cap on a filler spout it is not a problem. A small hole in the cap allows air into the tank. Placing a fuel tank under the cab seat in a truck without a spout brings up a problem. How do we vent the tank without having fuel vapor enter the cab while the engine is not running or how does it vent to the inside when the engine is running?
General Motors created an ingenious method of solving this problem. The attached photo shows a 1937 fuel tank cut in two halves. A hidden vent tube is installed vertically inside the tank.
IT SOLVES TWO PURPOSES
1. While setting without the engine running, vapors reach the 6 holes in the inside vent plate. If a light vapor pressure develops on a warm day (or in a warm garage) it is easily released under the tank through the vertical pipe.
2. When the engine is running, air enters the tank through this vent in a reverse flow as gasoline is pulled out by the fuel pump.
Vertical Vent Tube (tank baffle in background)
Close up of inside 6 hole vent plate.
Vent tube ending on tank bottom. (also see shut off valve and line connection to fuel pump)
Top of 6 hole vent plate assembly (also nearby, the opening for adding gasoline)
Tags: 1937 Gas Tank Venting