Gas pressure build up

Asked by Mar 27, 2010 at 04:31 PM about the 1973 Volkswagen Beetle

Question type: Maintenance & Repair

my 1973 VW Beattle keeps building up pressure in the gas tank. So much pressure that it forceses gas into the crank case and mixes with the oil. I have changed the gas cap, the fuel pump twice and tested the vent hoses that go into the tank , but the pressure keeps building up. Do you have any idea what could be causing the gas tank pressure?

3 Answers


Are you sure it is the fuel pressure and not a dead cylinder? How many pound of pressure does it develop? You might try adding a return line or a pressure regulator.

1 of 1 people found this helpful.

are you running the mechanical fuel pump? these pumps will not build pressure in the tank. they are a suction pump and will cause a vaccum in the tank if the vent lines are clogged. if you have a mechanical pump, and are getting fuel in the crankcase it's either one of two things. first is the fuel pump diaphram is broke. or the needle/seat valve in the carb is stuck. if you have a electric fuel pump, were is it mounted? they need to be as close to the tank as possible. they also will not build pressure in the tank, and they usually are not strong enough to pull much vaccum hench the reason to mount close to tank. if you have electric you need to measure your fuel pressure at the carb. anything over 5psi will cause problems. if it's more then you need a regulator. if you are running the mechanical pump you need to check pressure at carb also. some will put out over 7psi! if it's over 5psi then you can either put a regulator on it, or stack gaskets under the pump to lower the pressure. if you really do have a pressurized tank you got serious problems. maybe fuel lines hooked up backwards on pump?? take the gas cap off and run the car. do you feel air blowing out of the gas filler? do you feel it sucking air?

differnt person, same typw of car and same problem. my car actually built up enough pressure in the tank that the tank inflated like a balloon and when i took off the gas cap it spewed out like a volcano. car would not run with all this pressure built up but runs fine with gas cap loosened. the temp outside is a blitering 100 degrees if that matters

Your Answer


Looking for a Used Beetle in your area?

CarGurus has 9,020 nationwide Beetle listings starting at $1,600.


Volkswagen Beetle Experts

  • #1
  • #2
    Chris Billings
  • #3
    Tom Demyan
View All

Related Models For Sale

Used Honda Civic
356 Great Deals out of 53,229 listings starting at $1,200
Used Ford Mustang
274 Great Deals out of 38,355 listings starting at $1,995
Used Volkswagen Golf
67 Great Deals out of 4,830 listings starting at $600
Used Volkswagen Passat
314 Great Deals out of 26,776 listings starting at $1,500
Used Toyota Corolla
646 Great Deals out of 68,592 listings starting at $1,449
Used FIAT 500
92 Great Deals out of 3,764 listings starting at $2,844
Used Chevrolet Camaro
236 Great Deals out of 30,155 listings starting at $4,980

Used Cars For Sale

2018 Volkswagen Beetle For Sale
3,794 listings starting at $14,999
2017 Volkswagen Beetle For Sale
3 Great Deals out of 884 listings starting at $12,499
2016 Volkswagen Beetle For Sale
13 Great Deals out of 369 listings starting at $9,900
2015 Volkswagen Beetle For Sale
16 Great Deals out of 513 listings starting at $8,720
2014 Volkswagen Beetle For Sale
31 Great Deals out of 531 listings starting at $7,500

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.