Fuel tank pressure equalization

I just started experiencing a boom twice a day when my fuel tanks flex because of expansion or contraction. This is after 4 years of not doing that. I am assuming there is some sort of pressure equalization device on the fuel tanks that should prevent that. Does anyone know how that works? I have a 2019 Cyclone toy hauler with a fuel tank for the generator and a fuel tank for toys.


Well-known member
After filling our 2017 CY tanks, I tighten the caps until clicking, then loosen them 3/4 turn to the "stop".

If I don't back them off 3/4 turn, the tanks build up heat soak pressure.....when backed off, the pressure vents A-OK.


Well-known member
its because you have an EPA certified tank cap... which doesnt allow the tank to vent to atmosphere... loosening the cap should prevent the "oil canning" effect from expansion/contraction...
Thanks for the tips. When I backed off the cap 3/4 turn to the stop it works fine. Now I have to replace one of those caps. Does anyone know where I could get one. A manufacturer and model number would be great. There is neither on my caps and the auto parts places don't seem to be able to find one.