Surprised by the pressure?

I was fueling up the other day from a long road trip in the 355 and went to open then gas cap and noticed a unusually high amount of hot air exhausting from the filler neck. This does not seem right, Does anyone have a suggestion? It was a 80 degree day.

Thanks in advance

 

Well Ernie I found your post last year on the purge valves for the fuel tank.
Nice Pics, You saved me thousands..

 

Well Ernie I found your post last year on the purge valves for the fuel tank.
Nice Pics, You saved me thousands..

 

Wait...I thought in Ernie's imploding gas tank episode the air actually rushed IN, not out. Mine vents off all the time, so I hope so!!

 

Air rushing out = normal.
Air rushing in = purge valve problem.

 

Had the same problem recently, haven't had a chance to diagnose yet. I'll agree that some air coming out is normal BUT mine went from SOME air pushing out to a very large amount pushing out, over the course of one drive. Last time I stopped the car I heard a noise which sounding like a very faint door buzzer. Couldn't trace it, so killed the battery and it continued. Then figured the gas tank. Took the cap off to air forcefully expelling for almost a full minute. Guessing it's one of the valves, just haven't looked yet.

Charcoal canister clogged is another possibility, I believe.

Everything I've read suggests that there are vacuum problems with the valves, but I don't know if my overpressure problem is the same thing. Had the car almost three years now before this issue started, and I know nothing has been changed out in the fuel area.

Petervan, so what was your solution?

 

I have to do furthur investigation into the air expelling from the gas cap, But it occurs more motabley when the weather is hot.
Thanks so much for the feedback.

 

Egad, don't you guys drive your cars? This is totally normal operation. Pressure builds in the tank as the fuel atomizes in there. It's counterintuative, but less fuel = more pressure. Also, there is greater danger from flashing as that fuel charge rushes out so make sure you are grounded and have no static electricity on you - or you're not using a cell phone. LOL, actually this is a myth about the cell phone. Remember your engine runs on evaporated gasoline. The liquid form is just the fuel in a different state. Also, gasoline itself doesn't burn; it's just the top layer where it is atomized in the presence of oxygen. And in case you were wondering, the more you slosh that almost empty tank around, the more pressure you are going to release. >)

 

Sounds correct to me. Mine has always had pressure rush out infact the harder I drive it the more pressure builds up. Sounds like garrage queens.

 

12,000 miles in the last 2 years....

Which is why I KNOW that the pressure I USED to get when opening an almost empty tank in the hot weather is MUCH less than the pressure I got last time I opened the tank/ had the noise.

In addition, I never had the noise that sounds like a balloon slowly deflating after I turned the car (and battery) off. Yes Houston, there is a problem...

So there...

 

So your car has fixed itself and is now as it should be.
You have a hidden nanomechanic.

 

This sounds right