Unvented gas tanks

[briansnat]

I bought a new gas plastic gas tank for my outboard and the thing is not vented. That causes the tank expand like a balloon on a hot day. The thing looks as if it is about to explode.

Are unvented gas tanks a new regulation or did I just get a cheapie? If this is the wave of the future it's a stupid one. I can see one of these things bursting if it's a hot enough day. I tried to remove the cap to vent it a bit and it blew 5 feet into the air.

[dfish28]

You should get a cap with a vent in it, I personally saw an issue like this last season when a John boat at a dock had his vent closed and the expansive pressure forced the gas through the pickup into the bowl and with the engine tilted it was allowing gas to leak both into the boat and into the water, I opened the vent to drop the pressure, get a vented cap for that tank...

[Capt. Debbie]

Must have a check valve to let air in, but not vapors out.

I've seen that before. The pickup line becomes pressurized like a seltzer bottle.

[Treebeard63]

I have the exact problem..bought a new tank for my tin boat a couple months ago..which does have cap vent (with a rubber valve in it).. but even with the vent all the way open, it still swells up like a tick.. So I called the marine dealer that I bought it from.. I've known him for 30 years, and trust him.. he informed me that this is in fact due to a law change that took place within the last couple of years.. something about emissions.. He said the vent will eventually allow some pressure to release.. but it still makes me nervous.. I also worry about fuel being forced into the engine...