adding a vent to a gas tank

bigwaylon

Well-Known Member
Joined
Mar 22, 2005
Location
Charlotte
seems like the rear tank of my truck ('92 F-250) is building up excessive pressure...

do they make vented caps? or is there some other way that it should be venting off the pressure that builds up?

the motor is from a '79 F-250, and the truck originally had a diesel, so I'm not sure if something didn't transfer over, i.e. the diesel didn't need a vent but the gasser does?

the front tank doesn't seem to build up near the pressure the rear does...

Thanks.
Greg
 
Some caps are vented from the factory on diesal trucks. Most of the gas burners had a vent hose from the tank that went to the chacoal canister(look for a small plactic line leaving the tank it may be pinched). You can try swaping the caps between tanks and see if the problem moves. That would tell you if it the cap causing the problem.

Sam(slim)
 
got home this afternoon, and finally got to look at the truck...

first, a little background...I mentioned the excessive pressure buildup in the rear tank...the bigger problem arose yesterday...

I drove the truck to work on Wednesday using the rear tank, and parked it...taking a company truck to Asheville. I got emails from two different people Thursday afternoon saying I needed to do something, because there was a 4-6 ft gas puddle under my truck. One of the guys that emailed is halfway automotive knowledgable, and leaned under enough to see it coming right near the fuel pump.

Being over two hours away, I called up to CRS and asked Jeff if he or Chris could swing by. Chris got there after work and called to say it appeared to be running down the hose at the fuel pump, but without the key he couldn't pop the hood to see anything from above. I told him to take the rear gas cap off, and he said there was a huge "whoosh" sound as the pressure released. So, it built up pressure as I drove it up there Wed, then continued to build pressure in the heat on Thu, until the hose couldn't take it anymore, and was pushing fuel out at the fitting on the fuel pump. After releasing the cap, the fuel basically stopped running out, but he clamped the hose with vise grips as a precaution, until I could get by there today.

I figured it might be hard to start, thinking it may be flooded, but it fired right up and I drove it over to CRS. You could see the gas just running out, so Jeff crawled under it (I was still in BellSouth uniform, and he was already dirty...:D) and confirmed it did appear to be coming from that port, and not from anywhere any higher. So we tried to tighten the hose clamp, and then started checking for vent lines.

There is indeed a vent line on the front tank, but nothing on the rear. So, I just loosened the rear cap, and it didn't build any pressure when I drove it home. I guess the "fix" will be to drill a hole in the rear filler neck and figure a way to install a hose barb of some kind...and then just run a vent hose off of it...

...and then go back and replace the short section of hose between the pump and the hardline going to the tanks...

Greg
 
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