More on hissing fuel caps

[baby.driver]

I recall in past posts reading concerns members had with the hissing noise made when removing the fuel cap for refueling.

Some wrote of a cap on the vent on top of the fuel tank. Now before I go on to this "vent", let me quote from the shop manual for my 96.



Fuel Tank Filler Tube Cap



The loss of any fuel or vapor out of filler neck is prevented by the use of a pressure-vacuum fuel tank filler tube cap. Relief valves inside cap will release only under significant pressure of 1. 95 to 2. 5 psi. The vacuum release for all fuel filter tube caps is between . 14 and. 29 psi.



There is a little more and I don't know how they can use psi to refer to vacuum but it is understandable.



Now on to the "vent" on top of the tank. Shown in the shop manual is a top view of the fuel tank module. Inside the diameter of the plastic locknut are four components,



1) fuel supply/return

2) fuel gauge elec. connect.

3) pressure relief/rollover valve

4) aux. fuel supply fitting



I submit what people are taking for a "vent" is this aux. fuel fitting. I can only think this fitting should be kept capped unless it is being used for this mysterious "aux. fuel supply" or run the risk of a contaminated fuel tank.

There is no mention of exactly what they mean here. Is fuel being supplied to the tank here or running aux. equipment from that fitting? Your guess is as good as mine.



Jay

 

[illflem]

You are right there is an aux. fuel supply fitting that should be capped but there is also the pressure relief/rollover valve that shouldn't be capped but is on some rigs. The fuel tank module is shipped with the cap and it's supposed to be removed on the assembly line but not always is. Folks have reported having their fuel tanks collapse due to this oversight.

 

[Cooker]

Sometime back, I replaced my faulty rollover valve and the hissing has never returned. Thanks to Evan Beck for the suggestion.



-Ryan