Gas pouring out of vent tube?

moonlitcoyote · May 10, 2013, 09:12 PM

Awhile back I filled my gas tank and the next thing I knew I had gas pouring out of what looks to be a vent tube attached to the underside of the rear bumper. Since then I have not filled the tank, I usually just put about $100 worth of gas at a time so I never gave it another thought or got into it, but lately curiosity has got the better of me and I'd like to find out what is going on. Why does the gas come out the back when I fill it?... (That sounds like quite the opening for some wise cracks, I know) MJ

DaveVA78Chieftain · May 10, 2013, 09:58 PM

When you fill the tank the air inside has to have somewhere to go so there is supposed to be a ventline that allows air to escape as the gas flows in. The ventline is supposed to be attached to a nipple on the side of the filler neck within a few inches of the gas cap. Here is a example for a Chevy G series van that you can see the vent line running up alongside the main gas neck filling tube.:

You need to get under there and figure out how to reattach the ventline to the filler tube.

Dave

moonlitcoyote · May 10, 2013, 11:20 PM

Are you saying the vent line isnt supposed to be attached to the rear bumper?

DaveVA78Chieftain · May 10, 2013, 11:29 PM

Yep. Look at the picture above. See how the small vent line attaches to the larger fill tube close to where the gas cap is? Any liquid gas brought up the vent tube with the air is recirculated into the pipe and drains back into the tank.

Dave

MotorPro · May 12, 2013, 07:01 PM

Yes it is suppose to go to the bumper . It was put there as part of a recall on p-30 chassis. there should be check valve to stop fuel from coming out.

DaveVA78Chieftain · May 12, 2013, 07:58 PM

I see there was a modification for an 82 P30 chassis regarding potential issues during a rearend collision (http://www.dealerrater.com/recalls/Chevrolet/P30/) however I do not see any sort of recall modification that would have moved the location of the vent tube. Was this a Winnebago recall?
I do see in Appendix 7-8 of the Chevy MH Chassis Service Guide they addressed issues with aftermarket Fuels system design that could result in te issue MJ is having but nothing about a recall that moved the vent tube to the bumper.

Dave

moonlitcoyote · May 12, 2013, 10:33 PM

Well when someone figures it out will you let me know

MotorPro · May 13, 2013, 07:49 AM

Mine has the modification and has vents from both tanks running to the bumper.

DaveVA78Chieftain · May 13, 2013, 09:20 AM

MJ,
~~All I can say is I have not found any information that describes this change so if something is wrong I cannot help you work through it.~~

I think I stand corrected. Here is a reference to a Winnebago recall I found that I believe relates to this: http://www.recallowl.com/Vehicle+Recalls/Automotive/WINNEBAGO/CHIEFTAN/1985. It does not give details so you would have to contact Winnebago for information.

Dave

moonlitcoyote · May 14, 2013, 04:07 PM

motorpro, what is on yours that keeps the gas from coming out the vents on the bumper? Is there any way you could show me a pic of what to look for?

TripleJ · April 17, 2014, 12:31 PM

I just happened to search this subject since my tank is going back in soon.

Apparently there are different ways you tank can be vented. Dave posted schematic for one method, and if that is the only vent line to the tank, then here will need to be a vented gas cap installed. My tank has a different setup with two separate vents.

One is the 5/8" hose that connects to the tank near the filler hose and is intended to vent while filling the tank with fuel.

The second is a small 5/16" hose that connects to the tank at or near the fuel feed and return lines. This one is intended to allow the tank to "breath", and prevents pressure differential within the tank due to temperature or drawing fuel to the engine while the tank is otherwise sealed.

On older models without evaporative emissions systems, he smaller vent line simply has an orifice within the tube, and is run to an area where it is unlikely to draw in water, such as the rear bumper area, and left open to the atmosphere.

From the small vent at the bumper, there technically should not be gas coming out of it because the open end within the tank should be up high enough as to never touch liquid fuel. Mine is open about an inch from the top of there tank, so I would literally need to have it full to the physical top without an air gap.

Is it possible there may have been some work done to it and they connected the vent line to the wrong tube at the tank? Or possibly the gas pump you were using didn't shut off correctly, with the feedback thru the filler and overfilled the tank? Or maybe the angle of the earth in relation to the sun put your MH at such an angle.......

When I removed my tank, the small vent line was just a 10 inch piece of line hanging off the edge of the tank. This is cheesy and illogical and probably not the safest setup. I think I'll be running it up to the area of the gas filler door or something, and securing it to the big diameter fill pipe

Here is a pic of the vent lines on my style system. The thicker hose going off the bottom of the picture is the 5/8" vent that connects to the gas filler tube. The thin short length of hose hanging off the tank is the one that is open to atmosphere...

This is a close of the orifice in the hose. It is described in the service manual but it would take me a bit to find it...

I thought I took a better pic of this thing but I guess not. But you can make out the longest tube, that is the fuel pickup for the engine. The one that is an inch or two shorter is the pickup for the generator. The one you can't really see is only about an inch long, and is the vent...

circleD · July 07, 2014, 11:10 PM

I'm about to re install my tank also and I'm confused about all of these vents on the tank. Since there's a 5/8 vent hose going up beside the filler neck do we really need that smaller vent on top? I'm guessing it's 5/16 hose and not sure where to run it or if there's suppose to be a filter on top of it. My tank has 3 different fittings coming out of the top on the PS and on off them is only 6'' long (vent) and rotting. The other 2 hoses seemed OK but I'm replacing them anyway. I was just triple checking about this vent hose before I put it back in. The blue rag is hanging on the vent tube and the tank ground is just right of it.

TripleJ · July 15, 2014, 06:26 AM

Technically the 5/8 vent should connect to something under the gas filler cap, so that it only vents while you're filling the tank at the gas station. It SHOULD be closed off during operation.

The small vent should be open all the time on our systems to allow for thermal expansion and to provide air volume to replace consumed fuel. The only requirement is to run it somewhere that it won't suck up water...

I don't recall where I hooked either vent to right now. I will check that when I get home.

HandyDan · July 15, 2014, 11:20 AM

This is the end of the vent line on my HR.

circleD · July 15, 2014, 12:36 PM

Yes Dan, but that looks like a rear diff. vent. The ones for gas are suppose to have a charcoal canister at the end to keep the fume smell away or just have a good airflow so it doesn't build up underneath.
Sounds good JC, if you can get a pic of the 5/8 and smaller vent tip that'll be great. I'm going to try and reinstall the tank tomorrow.

budelkin · August 15, 2014, 01:09 PM

my 1988 class A 22' Itasca did the same thing, so I took the rubber hose off the bumper vent and plugged it. I have had no problems with it since, and did not need to vent the tank.

gpw9552 · August 23, 2014, 01:27 PM

If you click on the link in post 9 (THANKS DaveVA78Chieftain) and then click on the details button it will give you more information ie years covered etc.

The system on my '87 is a added "T" in the rubber vent line by the fuel filler. It is routed above the tank along the frame to the back bumper where it manifolds 3 plastic valves that vent excess pressure.