Siphoning Gas

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May 7, 2001 | 11:16 AM

jarch

Thread Starter

Junior User

Joined: Dec 2000

Posts: 80

Likes: 0

From: Lakewood, CO

Siphoning Gas

From the Aux tank to the Main (front) tank on my '78 F-250 4X4 Is driving me crazy. When I fill up the rear tank, the next morning, it says half full, while the main tank says completely full (when it was half full before). Furthermore, gas going to the engine will only draw out of the rear tank 'till it's empty, and then will draw out of the front tank - no matter which tank is selected with the selector switch.

Also, the main tank leaks a lot of gas out of the filling nozzle on warm days. Is there some kind of negative pressure developing in the main tank or what? What could be causing this and how do I fix it?

Could it also be a bad selector valve as well?

Thanks.

May 7, 2001 | 10:40 PM

weldman

Fleet Mechanic

Joined: Feb 2001

Posts: 1,290

Likes: 15

From: Toronto, Canada

Siphoning Gas

Try the fuel regulator that is mounted in front of the rear tank. $50 I think. Should control the siphoning problem! I had to replace mine because my rear tank would't let out fuel!

https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!

May 8, 2001 | 08:39 AM

jarch

Thread Starter

Junior User

Joined: Dec 2000

Posts: 80

Likes: 0

From: Lakewood, CO

Siphoning Gas

Thanks weldman.

Now, what exactly is a fuel regulator so I know what to look for. Is it on the fuel line? Is this different than the solenoid selector switch?

Thanks,
Jeff

May 8, 2001 | 12:38 PM

weldman

Fleet Mechanic

Joined: Feb 2001

Posts: 1,290

Likes: 15

From: Toronto, Canada

Siphoning Gas

See http://members.home.net/mattjibb/buildup9.html
Third picture down!

https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!

May 8, 2001 | 02:21 PM

tetraruby

Posting Guru

Joined: Mar 2001

Posts: 1,494

Likes: 0

Siphoning Gas

I had the same leakage problem on my '79 F100. The filler vent tube (the smaller one) had become dried out from repeated fuel swelling and no longer could seal well. It was a bear but I replaced it and the main filler tube after dropping the tank. Pressure shouldn't build - there's supposed to be a valve on top of the tank to release gas vapors into the Evap system.