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Fuel Tank -- Pressure?

Yahoo Message Number: 56000
I have been concerned about the vacuum pressure on my fuel tank..I have read numerous post about the vent line being stopped up., since I have been parked (nesting for winter) I have heard a couple of mini sonic booms I think from the tank releasing the vacuum., so I decided to investigate. Now the question!! After removing the inspection plate I find several lines going into the Tank, now my vent lines seem to be about 5/8" dia tubing that goes back to the fuel filler neck, below the cap so how does this procedure vent the tank freely? Also on my fuel cap it has vacuum only., I have 2 caps and both are the same.
Does anyone know where the vent is located that would relieve this vacuum pressure?

Marvin, 07 Allure, 470 42' siskyou summit., 31459

Re: Fuel Tank -- Pressure?

Reply #1 –
Yahoo Message Number: 56002
Marvin, on my 03 Intrigue, the vent line comes out of the top cap and runs toward the passenger side then down alongside the tank and is open ended about two inches above the bottom of the tank. On mine it is about 1/8 inch steel tube. If you crawl under the coach and look up at the fuel tank you should be able to see the vent line. Mine was plugged with road grime and under coating. I had to remove it and run a small diameter wire through it to clean it out.

Earl Densten

03 Intrigue 11554

Re: Fuel Tank -- Pressure?

Reply #2 –
Yahoo Message Number: 56005

Earl thanks, but I am wondering if between 03 and 07 if changes were made? Would you look at the fill cap and see what is written on it? Mine say Caution fuel may spray out when cap is released, and say vacuum pressure only...
I will look for the vent also!!
Marvin

Re: Fuel Tank -- Pressure?

Reply #3 –
Yahoo Message Number: 56007
Hi Marvin, I have the fuel cap in my hand and it is made by "STANT" and says "WARNING REMOVE SLOWLY FUEL SPRAY MAY CAUSE INJURY",it also say "VACUUM ONLY". During the winter months I don't think a pressure would occur and since the engine has supply and return fuel lines, a vacuum should not be too much of a problem.

Earl Densten

03 Intrigue 11554

Re: Fuel Tank -- Pressure?

Reply #4 –
Yahoo Message Number: 56009

That is the same as mine, the cap. I have been using the Hydra hot furnace quiet a bit, that is what I related the pressure to. I have always had the pressure suction or vacuum since I have had the Coach.. maybe I can find the vent tube...
I was thinking that after a certain amount of vacuum that the cap may release the pressure.. maybe someone else will know... How about all the CC guys... anyone know what the story is on the fuel tank pressure(vacuum)? Marvin 07 Allure 470 #31459

Re: Fuel Tank -- Pressure?

Reply #5 –
Yahoo Message Number: 56010
The tank should be vented to the atmosphere. The cap should have 2 lead plugs in the top that will blow out in the event of pressure or suck in in the event of vacuum. If you are getting either pressure or vacuum the vent is most likely plugged. Insects, dirt, undercoating can be the reason. The vent line should come off the top of the tank run down the side of the tank and end at the bottom. If you can get to the top where it goes into the tank, take that fitting loose and blow air thru it.

Mikee

Re: Fuel Tank -- Pressure?

Reply #6 –
Yahoo Message Number: 56018
Mikee,

Any idea of why the cap says 'vacuum only' on the top? I have asked everywhere and can't get an answer.

Don Seager

2004 Allure 31046
 

Re: Fuel Tank -- Pressure?

Reply #7 –
Yahoo Message Number: 56025
Most likely the cap is made to open (the lead plugs release) in the event of a vacuum. The caps have to be tested and made to do certain things. They probably never included pressure in that caps design. As long as the vent operated as it should it is not a concern. Another thought is pressure in the tank will not stop fuel flow to the engine, but a vacuum will, as the lift pump would have to overcome the additional resistance to flow caused by the vacuum.
The most important thing is to be sue the vent is open, you should not have pressure or vacuum in the tank. The fuel systems is designed as an open system, as opposed to gas engines of today that are designed to have a slight pressure in the tank. This is a direct result of the emissions laws that apply to gas engines.

So, just be sure the tank vent is working and all will be fine.

Mikee