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Gas Tanks

1937 Gas Tank Venting

Wednesday, November 16th, 2016

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.


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)

Gas Tank Baffles

Wednesday, November 16th, 2016

For the many people that have not seen a gas tank baffle, this should be of interest. These are usually flat metal dividers welded inside a fuel tank. They slow the side to side movement of the fuel. Numerous openings between the welded dividers cause a slower movement of fuel. See Photo.

Baffle Trivia!

1. All tanks in a vehicle that moves must have baffles so a sudden sharp turn or stop does not cause all the liquid contents to instantly surge to one side of the tank.

2. The surge of fuel can even uncover the low filled fuel tank’s pickup inlet so the engine hesitates or stops.

3. Noise of fuel moving from side to side can create an annoying sound if near the passenger area.

4. On early vehicles the fuel can be forced out of the fill inlet to drip on exterior paint or running boards.

5. Example of a non-baffle moving tank with liquid inside: Ever been behind a yard spraying truck moving in a neighborhood? The liquid fertilizer or insecticide freely moves from side to side
as the translucent plastic storage tank is moved on the side streets.

1937 Chevy truck tank cut in half showing one baffle

1939-46 Under-Seat Gas Tank

Tuesday, February 23rd, 2016

Finally we have just received another large delivery of 1939-1946 Chevrolet / GMC metal gas tanks. The demand picked up faster than we expected so we had been without for about six months until our order for our tanks, was manufactured and shipped. The manufacturer makes over 100 gas tanks so we had to get in line!

Ours are the best on the market. Made to exact GM specifications. They are even zinc plated inside like original so rust does not appear for many, many years!


These 18 gallon metal tanks are made for the safest place on the truck. Here’s why.

1. They set below the seat assembly and are surrounded by heavy 12 gauge ribbed steel band that is welded to the cab floor. (Almost impossible for most body shops to straighten this heavy plate)

2. This is surrounded by a cab with two layers of 16 gauge metal. (also not easy for most body shops to straighten dents)

3. There is no rubber hose connection to leak between the tank and the gasoline add pipe.

4. Just below this gas tank is the two long steel frame rails as well as a heavy cross member just behind the rear edge of the cab.

5. The narrow distance between the drive line and the frame rail prevents placement there without it being a very small size. This would require frequent refills.

Yes, General Motors knew the safest place for their tank!!

QUESTION! We have seen restorers place a non-original tank behind the rear axle. WOW! Could this really be happening? That’s a bomb ready for a rear end collision. Remember the 1978 Ford Pinto car fire disaster that killed 3 people? Check Google on your computer and then “Ford Pinto Fire”. This may bring back some memories.

Your gas tank is an area surrounded by three layers of steel! Placing it behind the rear axle with almost no protection puts it in a very dangerous position.
Protected by 3 layers of metal, 2 frame rails, and a cross member

And this owner really thought it was safer than GM did it!

1934-36 Chevrolet Low Cab Gas Tank Changes

Monday, June 29th, 2015


If you have one of these unique low cab Chevrolets (made about 6 months) you might have not realized there are two gas tank locations.

For ½ tons (116”WB) the 16 gallon gas tank was positioned between the frame rails and just behind the rear axle. The mechanical fuel pump on the right side of the engine pulled the gasoline about eight feet distance to the carburetor.

½ ton gas tank position between rear cross members



A change was made with the 1936 low cab 1 ½ ton trucks. Chevrolet continued to realize it was not acceptable to have the tank so far from the fuel pump on a long wheel base. Therefore, a 17 gallon tank on both the longer 131” and 157” wheelbase continued to be placed under the seat cushion.

Remember: The cabs are almost the same on the ½ and 1 ½ so the only universal place available was below the seat cushion! On the longer wheel base 1 ½ ton trucks the passenger door was opened to get access to the gasoline fill that was inside the cab. This had been the way to add fuel since 1934!

The late 1936 1 ½ ton (low cab) were all the same except in the gas tank related area. Here is why!

EDITORS OPINION: In 1936 and earlier, the USA was experiencing the height of the Great Depression. Car and truck sales we show and most everyone was feeling economic slowdowns.

General Motors looked for ways to cut expenses, especially on truck production. They were workers not pleasure cars. A perfect example is changes on the 1936 Chevrolet 1 ½ ton. The new truck under seat gas tank was planned due to complaints and a side fill added. This would eliminate the inconvenience of raising the bottom seat cushion to add gasoline. Unfortunately, so many of the older designed tanks remained stored for future truck production. GM was not about to dispose of these new tanks during the depression so they used them until their supply was eliminated.

It was much less expensive to be ready for what was coming later in the year. It was a matter of economics! Therefore, the stamping in the right seat riser and scoop in the inner door panel was part of the 1936 1 ½ tons. When the extra tank supply ended, it would be inexpensive to have the truck ready for the new design.

We thought this might be of interest to the perfectionist with a 1936 Chevrolet 1 ½ ton low cab.

Late 1936 1 ½ ton gas tank spout

Under-seat cushion positioning on late 1936 1 ½ ton

Oval dent in door panel on all 1936 1 1/2 tons


Without the spout on early 1936 1 ½ tons.

Economical Gas Tank Cleaning

Friday, July 19th, 2013

We recently had a local radiator repair shop clean the rust from an older used gas tank.  They submerged it in a cleaning acid tank overnight.  The price was $65.00.  WOW!   Several months later we discovered an “old school” method that would have cost about $1.00.  Oh well, we live and learn.

Back in the days of the Great Depression money was a scarce commodity and economical methods in life were used or otherwise things probably did not get done.  It was discovered that agricultural molasses (not what you buy in the grocery store) mixed with four parts water removed rust.  Fill your tank with this combination and wait about a week.  Surprise!  Your gas tank is shiny clean inside.

You can even put a lid on a five gallon bucket from a hardware store and small parts covered with this formula will have all the rust removed in less than a week.

Agricultural molasses is used to mix with livestock feed.  It causes farm animals to eat otherwise less desirable feeds because of its attractive sweet taste.

Retail price at a livestock feed store is about $2.00 for 10 pounds.

This data is provided by MIKE RUSSELL of COLUMBIA, MISSOURI.

Another cleaning Technique!

Several years ago, we heard of a gas tank cleaning method that cleans most tanks every time and its FREE!

Attach the gas tank to a farm tractor large rear wheel before a day in the field.  Add about a pint of ¼” gravel.  The slow rotation of the large wheel will move the gravel continually inside the old tank.  Sometimes even by noon, the rust is all removed as the gravel continually moves inside the tanks. Just pour out all contents and the tank is cleaned!

1939-46 1/2 Ton Suburban/Panel Gas Tanks

Tuesday, November 29th, 2011

The gas tanks are totally different on the more common pickup versus the panel truck/suburban body, though the two frame rails, drive train, and front sheet metal are the same on each 1939-46 ½ ton.

On pickups the 18 gallon tank sets comfortably and safely within the seat riser and below the seat cushion. Over a million of these pickups were sold during this production period.

The panel truck and suburban were totally different animals. They had no protective seat riser. In fact, there was not even a passenger seat in most panel trucks. For protection, their 16 gallon gas tank was placed inside of the right frame rail and under the body. This gives the tank the safety of the frame rail and being in front of the rear axle. In the attached photos, the totally different shape of the panel and Suburban is quite obvious.

Gas tank removed from a 1941 panel truck.

1939-46 1/2 Ton Suburban/Panel Gas Tanks 1939-46 1/2 Ton Suburban/Panel Gas Tanks
1939-46 1/2 Ton Suburban/Panel Gas Tanks 1939-46 1/2 Ton Suburban/Panel Gas Tanks

Under the seat tank (usually on smaller trucks)

1937 to Early 1938 Chevrolet /GMC Gas Tank and Seat Cushions

Monday, August 22nd, 2011

So unusual to place a gas tank under the seat with no fill pipe outside the cab! To engineer this big change for 1937 was expensive and very different from earlier years when it was under the bed. Why was this done? What advantages could this have been over an outside fill spout? Was gasoline theft during the depression years a big problem?

To add gasoline on a 1937, the right lower cushion half was raised up toward the back which exposed the threaded ‘bung’ on the surface of the tank. It meant a person stood outside by the right side of the cab, raised the cushion half and added fuel. This is how it was done! If it was raining or snowing, the driver or the attendant stood there fueling. Maybe you kept an umbrella stored in this small cab for emergencies. Maybe gas station employees knew that when a 1937 Chevrolet or GMC truck drove in to get gas in the rain, a raincoat was needed. If some gasoline was spilled while filling, the vapor was smelled throughout the cab. If you were a cigarette smoker, well—–!!!

We were fortunate to recently obtain a set of 1937 original seat cushions. Even the upholstery on the two lower halves was still intact. The non-spout gas tank from the same truck came in the set.

Before they were requested by a serious collector, pictures had to be taken. Finding a pure set again in one place would probably be impossible.

An interesting feature is the plywood bottom on the right side removable cushion. The rectangular hole in the plywood prevented the springs from ever sagging and touching the electric gas sending unit. This must have been placed there to also protect the gas tank and bung from contact with a passenger’s weight on the seat. Engineers knew that a spark from an electric short near gas vapor would be a disaster!

We think these photos will be very interesting to the 1937 GM truck enthusiast. This way of tank filling continued into early 1938. Probably during the depression years, the manufacturer used their extra bodies and tanks that were left over from 1937 until supplies were depleted. Of course, this changeover would vary depending on the assembly plant.

The in- cab gas tank is also unique. It lies neatly inside the seat riser. The twist cap (bung) hole for adding fuel is at least 10′ away from the sending unit (protection from a gasoline pump add nozzle). For some reason the tank is built with two drain holes. One is always plugged and therefore the tank can be used in two type cabs. Maybe the gasoline outlet is different for right or left hand drive trucks!

Both Cushions have original upholstery Easily removable wood bottom half cushion. Note: the 2 small blocks to keep cushion secure on the seat riser.
Open spring half cushion for driver Both cushions raised above gas tank.
Plywood notch fits above gasoline sending unit. Sending unit in place.
Gasoline add bung and adjacent air vent. Open bung during refueling.
Top of tank. Note: Sending unit, bung, and air vent. Bottom of tank. Note: 2 Gas outlets.

Amendment to 1937 to Early 38 Chevrolet / GMC Gas Tank and Seat Cushions:

Several years after the above article was posted, a pair of original bottom cushions appeared at our shop. The owner stated they were from a 1937 pickup that had been in the family since it was a year old.

As the underside is covered with a sheet of rusted thin metal, it would appear it is original GM. We now wonder if the wood plywood bottom in the first article is factory installed or the result of a very skilled carpenter attempting to add additional years to a deteriorated set of original cushions. You be the judge!

SURPRISE:  As of December 2016, new 1937 gas tanks are in stock.  Just like GM made them 8 years ago!

Early Gas Tank Changes

Thursday, February 11th, 2010

During the three years of this cab design, subtle changes occurred as GM engineers learned better ways to construct this truck. The gas tank changes on the pickup body style was probably the most obvious and it was different each of the three years.

In 1936, the new mid year low cab pickup continued with the earlier practice of securing the tank under the bed and behind the rear axle. The gas add spout extended through a hole in the lower bed side behind the right rear fender. Thought it might seem like a good location, it was not. Considering the trucks stiff suspension the poor roads of the 1930’s, and how rough trucks were treated, this location resulted in tanks leaks and cracked fuel lines that were over 6 feet from the engine.

The answer to this problem came out in the 1937 trucks. The tank was moved to the protected area under the cab seat cushion. This solved prior problems but the improvement did not go far enough. The fuel add hole was in the top of the tank on the passenger side. To gain access to the threaded plug to add fuel, the right side of a new split bottom cushion was raised or removed. Rain or shine, the passenger would stand outside and wait for fueling so the seat cushion could be replaced. Of course, any accidental spills or splashing from the spout would give fumes within the cab till the evaporation was complete. What if you lit a cigarette out of habit? What about a small electrical short under the dash? Your imagination can tell you what probably happened a few times over the years.

The engineers seem to have got it together in mid 1938. They redesigned the 1937 tank and cab so that gasoline was added through a spout that now extended out the cab corner. The bottom seat cushion was then one piece, however, for several months two piece bottoms were still used on the assembly line until supplies were exhausted. Therefore, the late 1938 tank was used less than one year and is very rare today. The new designed 1939 body style continued with this type tank and cab design but the 39 tank will not interchange in the earlier cab.

early gas tank changes 1

1937 ( above)

early gas tank changes 2

1937 (above)

early gas tank changes 3

1937 (above)

early gas tank changes 4

1937 (above)

early gas tank changes 5

1938 (above)

early gas tank changes 6

1938 (above)

early gas tank changes 7

Gas Spout Hole from Outside

early gas tank changes 8

Gas Spout Hole from Inside

1937 – 1972 In Cab Gas Tank – Friend or Foe

Thursday, February 11th, 2010

What’s this bad rap some people give the GM pickups with in-cab gas tanks? For 35 years GM protected these tanks from collisions by double wall reinforced cab metal, doors, and seat frames. The 1937-46 pickups even secured the tank under the seat and surrounded it on three sides by the welded to floor heavy metal seat riser.

If you and your truck are ever involved in a collision so major that the gas tank begins leaking, then imagine what could be occurring if the tank was in most other places on the truck. Unless you have found a narrow tank that fits inside the frame rail and away from the drive shaft, you haven’t located a safer location than what GM used between 1937 and 1972.

For approximately 18 months, beginning with the 1947, Advance Design body style, GM placed their pickup gas tanks under the bed inside the frame rail. This location, while protected from side impacts, was very susceptible to damage from road debris. Leaks from being hit by rocks and stumps soon caused GM to again place the tanks in the cab. Possibly, a protective panel would have given the tank a shield but GM did not use this option. The tank went back in the cab.

In these older trucks you instantly smelled gasoline if the sending unit gasket or gas filler hose began to fail. Trucks with under the bed tanks usually must be parked and dripping before a person smells the vapors.

Important:  If you critique the early in-cab GM gas tanks, don’t forget what General Motors did to the truck series beginning in 1973. Can you believe? They secured the tank in their pickups to the outside of the frame rail under the bed. The only separation from a broadside accident is the single layered sheet metal bedside! It doesn’t take much of a side impact to flatten the tank with disastrous results.

Currently, the nervous owners of some earlier pickups move the tank out of the cab and place it under the bed behind the rear axle. This new tank position is definitely exposed to major damage from a heavy hit at the rear. An original in-cab tank is nicely protected from most of these rear and side impacts.

Remember, a Ford Pinto car being rear-ended in the 1970’s?  Their gas tank was behind the rear axle.  The resulting explosion and fire killed the occupants.  The Ford Motor Company paid dearly for that one.

Don’t make your truck more dangerous than it was originally!!

in cab gas tank 1

An in cab underseat gas tank as used between 1937 -1946…It lays inside a metal seat riser as well as being inside a heavy guage metal cab. (above)

in cab gas tank 2

The above photo wa taken of a 1952 Chevrolet 1/2 ton daily driven pickup. The owner was so concerned about the gas tank in the cab that he placed it under the bed behind the rear axle. The non metal tank is just waiting for a rear end hit at about 20 miles per hour. The original bumper will offer little protection and the contents of the tank will fly in all directions…Is this a moving bomb ready to explode?

Leather Gas Grommets

Thursday, February 11th, 2010

The United States and its allies suffered from major rubber shortages during World War II as the Japanese had control of most Indonesian rubber tree plantations. To survive without this material, much of the world was forced to settle on a limited supply of synthetic rubber of lesser quality. This material filled some needs but lacked the strength and durability of real rubber. Synthetic tires got half the mileage and this material had limited resistance with contact to solvents such as gasoline.

Leather Gas Grommet 1

This created immediate problems with the gas tank grommets on GM trucks. (This rubber ring seals the hole around the large gasoline add-pipe extending from the tank through the right side cab corner.) A synthetic rubber grommet was not practical in this location because of occasional gasoline spills during fill-ups.

Leather Gas Grommet3 3

A solution to the problem was using a proven material that was readily available in the U.S. It was leather! On the assembly line a punched leather disc was pressed over the gas add pipe and held in place against the body with a metal attaching ring. Four screw holes were punched in the body and ring at the factory for the screws. This leather grommet was not equal to the original rubber unit, but did hold its shape against the elements.

Leather Gas Grommet 2

Therefore, you can always identify a GM truck cab from this era because of the four punched holes beside the gas hole. The rubber gas grommets used before the war and after about mid 1946 will not totally cover these four small holes. Unless they are filled, by a body shop, the cab must remain the World War II type with the leather grommet.

This is not a bad thing.  The leather fits well and you have a great conversation item on your WWII truck!