Caution
Tank swelling will occur. EPA regulations have eliminated the traditional venting in these tanks. New portable outboard marine fuel tanks will not vent below 5 PSI with noticeable swelling. The new cap will cause the portable outboard marine fuel tanks to swell. The swelling is a result of the fuel vapor building pressure because the cap must stay sealed up to 5 PSI. The new tanks will remain sealed and safe at these pressures even when swelling is visible.