Intense venting of gas while four wheeling.

[sanchius]

My son, daughter and I were running Colorado forest road 118 (36/SR47/johnny park/Big elk meadow to meeker/peak_to_peak highway) in our '86 60 this weekend. The trail was great fun, a beautiful forest trail with a few technical parts, all do-able with stock suspension/tires and a 17 year old doing all the driving.

But we did experience something very strange. After an hour or so, as we crested the top of the trail mostly using 1st and 2nd in low range, I heard a strange sound from the rear. We stopped and it was coming from the gas filler cap. We shut down and I carefully opened the cap and there was intense venting of gas vapor from the gas filler, almost as if the gas in the tank was boiling. The tank itself was hot and the vapor was hot. Naturally, we got well away until after about ten minutes it stopped, we started up again and finished the trail without event.

Has anyone else experienced this or have any theories on what caused it or how to avoid this in the future (such as heat shielding the exhaust in the rear)?

 

[Dynosoar]

Most likley a pluged or cloged up evap system.

Dynosoar

 

[High Desert]

As you gain altitude the system will gain pressure because there is less atmospheric presure (that bag of chips did the same by swelling up). I understand that all modern, (even 20 year old) fuel system are suppose to be under pressure, it sounds like your gas cap may be losing it's seal because I don't think it should "make Noise" and vent like that.

If the tank was hot it it would seem it could only be a exhaust leak near the tank..But one would think it would otherwise get no hotter than a tank sitting in traffic in Dallas on a 110 degree day cooking over the asphalt...

My tank is always Under Pressure when I remove the cap, winter or summer even if it has been sitting in the garage, as long as it's been run some since the last time the cap was off. I live in the cascade mts. very often the cap will almost get blown out of my hand as the tank depressureizes (sp) at fill ups.

 

[sanchius]

The thing that has me stumped was the fact that the vapor venting went on very strongly for 10 minutes with the gas cap completely off and the engine turned off. The flow rate was similar to the output of a vacuum cleaner or shop vac. I'd never seen anything like it.

One of the purposes of the trip was to stop by the B-24 fire bomber crash site (across from the Lion Gulch pulloff, between milemarkers 8-9 off 36 SE of Estes Park) on the way back. The last thing I wanted to happen was to have that vapor to ignite and start a forest fire.

It was also a bit alarming when we started up again and the gas gauge read nearly empty. However, it returned to showing the proper 1/2 full state soon afterwards.

The good thing was that engine itself never missed a beat, either before we stopped or afterwards.

 

[agent orange]

I gotta say, the title of this thread is a bit deceptive. I had envisioned more of a check your pants moment with others looking on in horror.

 

[Waggoner5]

It sounds like the evap system is not working properly. Check the VSV up front that has the vacuumm hose running to the charcol canister. It should be labeled VAC. This hose has intermittent(sp?) vacuum to keep a small amount of vacuum on the tank to keep this from happening. Follow this hose to the VSV valve. This could be your problem. I have seen them go bad on occasion.
One reason the fuel and tank get hot is that when crawling along most of the fuel is routed back to the tank from the regulator. The fuel runs up to the engine, sits there a minute and is sent back to the tank all heated up when its not used. This is common and theres not a lot you can do about it. The VSV must work to depressurize the tank.
G

 

[dieselcruiserhead]

Gary is exactly correct particularly about the fuel heating up. Nothing wrong with it, its normal after good long driving. This is also the same with many vehicles with mechanical fuel pumps..

 

[pvidrummer]

The thing that has me stumped was the fact that the vapor venting went on very strongly for 10 minutes with the gas cap completely off and the engine turned off. The flow rate was similar to the output of a vacuum cleaner or shop vac. I'd never seen anything like it.

Thats insane. It must be the evap system thats clogged and not releasing the built up pressure. I think your vacuum cleaner gas tank was caused by a combination of things: clogged evap system, high altitude, hot recirculated gasoline, and most importantly the sloshing of the fuel while you were on the trail. Also the fact that the tank was 1/2 filled with gasoline left the other 1/2 to be filled with compressed air. I beleive you sanchius, and I also beleive you should check the evap system pronto!

 

[sanchius]

It did feel like a fuel recirc & heating situation like I've seen before on high pressure FI systems, but I had assumed that they didn't recirc the fuel on the carb'd setup.

I just crawled underneath and saw that they properly designed the fuel and exhaust systems to run on opposite sides of the frame. Time to check out the evap system and insulate the fuel lines in the engine bay.

Thanks for all the great help.

And, thanks, agentorange. Now whenever I reread the title of this thread, a rather hideous, yet strangely funny, image comes to mind.

Sanchius

 

[alpendubber]

Sanchius,

Hey, I live in Glenwood Springs and am having the same problem. I only experience it badly when my tank is full. This problem just started over the weekend. I filled up in Carbondale, drove up Mclure pass, then Kebler and camped at Lost Lakes. When I got to camp, I could hear my gas cap humming. It has no cracks but there was so much pressure it was leaking anyway. It vented like yours for close to ten minutes. It's funny that mine just started doing this, two weeks ago I did Ouray over Imogene pass to Telluride, then Ophir to Silverton and back to Ouray with no problems.

Did you replace that valve? Did it fix the problem?

Thanks

 

[cwb]

Mine has done the same thing. Sort of a high-pitched hum. Doesn't do it all the time, but on occasion, I'll shut off the engine and hear it. When i do, I just release the gas cap and put it back on. But I'm sure there's a minor problem somewhere.