Vented gas cap?
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Fleet Mechanic
Joined: Jan 2007
Posts: 1,847
Likes: 37
From: Eastern shore,Salisbur,MD
Vented gas cap?
Hi gang. Beautiful weekend for a drive.
The other day, truck was a little stubborn to start. This truck starts the instant you hit the starter. This particular time, it was acting up a little. I checked the see thru gas filter and there was room at the top. Normally, it is full . I opened the gas cap and heard a whosh. Now, the cap I have is supposed to be vented, according to Mid Fifty. Since then the truck is running great. Drove about 40 miles yesterday. ( Background New tank, lines, rebuilt fuel pump. I do not understand why pressure ( or vacuum ) is building up if it is a vented gas cap. It appeared like a plastic gas can you leave out at night and in the morning it is all sunken in. Any ideas or help would be appreciated.
The other day, truck was a little stubborn to start. This truck starts the instant you hit the starter. This particular time, it was acting up a little. I checked the see thru gas filter and there was room at the top. Normally, it is full . I opened the gas cap and heard a whosh. Now, the cap I have is supposed to be vented, according to Mid Fifty. Since then the truck is running great. Drove about 40 miles yesterday. ( Background New tank, lines, rebuilt fuel pump. I do not understand why pressure ( or vacuum ) is building up if it is a vented gas cap. It appeared like a plastic gas can you leave out at night and in the morning it is all sunken in. Any ideas or help would be appreciated.
Logistics Pro
Joined: Nov 2006
Posts: 3,674
Likes: 367
From: Fallon,NV & Bainbridge OH
A vented cap is designed to replace air in the tank as fuel level drops but it is not supposed to allow gas vapors out. So tanks can build pressure as they warm up if they are just sitting. So was your whoosh an inny or outy whoosh?
Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
If you want to verify that your gas cap is in fact vented simply remove it and put your mouth over the center hole (on the gas tank side) and suck in. If you can suck in, it's vented. If not, it isn't vented or the spring is faulty. Note: You shouldn't be able to blow out as the vent only works one way.
Thread Starter
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Fleet Mechanic
Joined: Jan 2007
Posts: 1,847
Likes: 37
From: Eastern shore,Salisbur,MD
Thanks Dave and Calvin. My internet has been down for a little bit. Rain in the cable. They are still working on that issue.
I checked the other day, It appears that it is an outward whosh. I will try right now to try sucking in on it. I will let you know how I make out. In the mean time Mid fifty is sending out another cap. They have been good to work with.
Thanks again
I checked the other day, It appears that it is an outward whosh. I will try right now to try sucking in on it. I will let you know how I make out. In the mean time Mid fifty is sending out another cap. They have been good to work with.
Thanks again
Thread Starter
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Fleet Mechanic
Joined: Jan 2007
Posts: 1,847
Likes: 37
From: Eastern shore,Salisbur,MD
So I am not really sure what transpired with the tank the other day. Possibly, the cap could have got stuck once. In any case, I put the new cap on it from Mid Fifty, All seems good. The one thought is that there could be some type of a blockage in the tank, but as i said, everything was new. I'll just have to see how it goes. I wish I had one of those long flexible camera things. I would look in the tank.
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