Ask the Editors: Help! My Gas Cap Freezes Up

Goes on easy. Comes off hard.

The reason this happens is due to the nature of gasoline; which is not only highly evaporative but prone to making intense vapor pressure. Anyone who’s ever opened their plastic gas can in a hot barn on a summer day has surely witnessed this phenomenon in action in the form of a hiss/ pressure release.

When you put your ATV’s gas gap on, there is minimal pressure build-up in the tank (because it’s open and exposed to the atmosphere). Over time, however, that vapor pressure builds inside until the tank itself begins to expand. The expansion literally deforms the tank just enough at the threads to make the cap difficult to break loose.

We have a few caps that are notoriously tricky this way. The best solution we’ve ever found is to keep handy a small hammer or mallet and a rag. Place the rag over the cap and tank then tap the finger grips of the gas cap with the mallet to the left. After a few steady (but not hard) whacks, the cap should break free and become easy enough to turn the rest of the way with your fingers.

If you aren’t seeking a solution to the situation but rather the problem itself, sometimes switching to a larger vent hose can alleviate the pressure causing the tank swell. We’ve also heard of riders switching to caps of a different material (like from plastic to a metal cap or vise versa) having success.

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