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Coach & Powertrain: Evaporative Recovery System

Originally Published in MotorHome Magazine

I have a problem with very high gas tank pressure. I have a 2006 Class A Fleetwood Bounder with a Ford V-10 engine. I realize there is a certain amount of pressure in a tank; however, a bang can be heard and felt when the tank expands. I recently made a trip in Florida and was running my generator using the A/C for cooling inside the coach. The generator stopped running and I pulled over to check and found high enough pressure in the gas tank to shut off the generator. When I released the pressure the generator started. This happened several times, so I loosened the cap and was able to release the tank pressure. I don’t believe the fuel cap is the issue, with the amount of pressure build up. Can you help?

— Brad Tyler | Phoenix

The gas tank has an evaporative-recovery system and uses check valves to allow air to enter the tank as fuel is consumed, and for pressure to escape when the fuel and air expand as they get warmer. Usually when the genset quits because of a problem like this it’s because of a partial vacuum (lower pressure), not excess pressure. Try changing the carbon canister. If that doesn’t help, change the gas cap or take it to a chassis dealer for evaporative system testing.

— Ken Freund

Man smiling and standing next to truck driver side

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