1997 F350 SRW 4x4

I left this truck with my dad about 6 months ago - recently he called and said all the fuel from the front tank was ending up in the rear tank.

My first though was the selector valve was returning all fuel to the rear tank - then he told me this was happening while the truck was sitting overnight - engine not running.

My next thought was a clogged vent causing the front tank to pressure up and push the fuel somehow into the rear tank. I suggested he fill both tanks 1/2 full and leave the fuel caps loose to let the air out and see what happens.

He said the next morning the front tank was empty and the rear tank was full.

This seems impossible to me - but this is what he told me today -

Anyone seen this before or can shed any light on this - please help -

Thanks
4K

 

Its a tank selector valve problem.

 

Could the fuel cap be bad as well? (not allowing air back in to the tank as the fuel drains?....I dunno, still kind of early and I am not up to my normal 20%, yet...just throwen some ideas out there).
Can he try to switch caps?

 

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DELETE, just a test

 

bump. Does anybody knows what happened?