Excessive fuel tank pressure

[MaddBaggins]

I really think people are discounting exactly how much vapor is being released for how long in this thread. 10 minutes of off gassing is a very significant volume. In order to produce these volumes of vapor a significant heat source has to be boiling the fuel somewhere in the system. The difference in the boiling point of nonethanol gasoline and pure ethanol is only 7 degrees. 87 octane fuel boils at 180F at sea level ethanol at 173F at sea level. I would look for heat sources close to the gas tank to trouble shoot this mainly exhaust gaskets or damaged/missing heat shields.

I live at 2500' and any time offroad is generally above that, lowering the boiling point further. Heat off the pavement in Tucson during summer has been documented as high as 140 IIRC. I would guess it could be 150+ in PHX. Heat sources near the tank are definitely adding to the overall heat. The muffler is pretty close to the tank. I've redone all of my exhaust years ago with larger tube and a more hi flow muffler. I would guess the heat is passing more freely out the back end rather than building up but I have no documentation of that.
Having had this rig since 2004, I never noticed an issue the first 3-4 years. The issue began around the same time that all Tucson stations began selling the ethanol blend. Then I started this thread in 09.

I've pretty much given up on it but still follow this thread to see if anyone else comes up with something good.

 

[MaddBaggins]

I found the heat source

It's always sunny around you, Phil.

 

[MaddBaggins]

Are you working on CCR? We have UOP unit that typical to 101-106 RON because the lowest grade of gas in Israel is 95 and we have 98 in all gas station mandatory. No ethanol (some times, some MTBE)

And we have summer and winter blends

In Tucson most station are 87 - 91. I've gassed up at smaller places out of the city with as low as 85.

 

[MaddBaggins]

Saying that gasoline boils at a certain temperature is telling only a small part of the story. The fuel in our trucks is made up of many different components with the lightest of them start boiling off around 100 degrees at atmospheric pressure and going up from there. The hotter you get the heavier the components will start to vapor off. The end point of your typical gasoline is around 400 degrees which means it takes that much heat to boil off all of the heaviest components in there.

If it wasn't so late and I wasn't so tired I would elaborate a bit more. But I run the console (think Homer Simpson) of 2 different units at an oil refinery. One of them is a reformer which takes in heavy naphtha with an octane rating of around 50 or so and bumps it up to anywhere from 85-100 RON, just depends on what the needs are.

I'd forgotten some of that. I don't recall if thats been mentioned way back in this thread. On a typical summer day, even if I haven't driven my rig, the gas could easily be sitting at 120 depending on where I parked it.

 

[alia176]

fellas, I need some clarification please; when you say "boiling", do you actually mean boiling water on the stove top like boiling? The fuel is doing the boiling thing inside the fuel tank?

 

[LandCruiserPhil]

fellas, I need some clarification please; when you say "boiling", do you actually mean boiling water on the stove top like boiling? The fuel is doing the boiling thing inside the fuel tank?

Yes, Stove top type boiling

 

[MaddBaggins]

fellas, I need some clarification please; when you say "boiling", do you actually mean boiling water on the stove top like boiling? The fuel is doing the boiling thing inside the fuel tank?

Yep, I can hear it when I shut the rig down. I opened the gas cap once and gas came spewing out at me.

 

[BILT4ME]

fellas, I need some clarification please; when you say "boiling", do you actually mean boiling water on the stove top like boiling? The fuel is doing the boiling thing inside the fuel tank?

Because at higher elevation, the vapor pressure on top of a liquid is lower and thus, the boiling point is lower. At sea level, water boils at 212°F. At 7500 ft ASL, water boils at 198°F.

Fuel that normally boils at 120°F will boil at 112°F. If the truck is hot and the fuel is recirculating and heating up, it can easily boil at elevation.

 

[Desert Dino]

Let me tell you a secret
Some time C4 (Butanes) compounds are added to the blend to reduce the density of gasoline that is sold by volume not by weight LOL cheaper for producers.

Especially in cold countries this is boiling at elevated places and of course Ethanol

 

[utahisrad]

Add me to the list. Every time I fill up and take the cap off it depressurizes for a few seconds. On some of my trips I have smelled gas, never noticed the boiling thing before. Thanks everyone for looking into this. Still not sure what the fix is but I will keep reading

 

[Nay]

I have a Murphy Express that opened recently near me that sells an ethanol free 87 octane (85 is typical in CO).

I live at 7,400 and run that fuel when headed to the High Country. I’ve never had a boiling problem, but do get a vapor smell when it’s warmer and have for years despite changing out the charcoal cannister. The ethanol free helps with that problem @ a $.40/gallon or so premium.

Not sure what the deal is with ethanol-free availability generally as it was impossible to find, so I’m happy to see it as a regular option.

 

[BILT4ME]

Add me to the list. Every time I fill up and take the cap off it depressurizes for a few seconds. On some of my trips I have smelled gas, never noticed the boiling thing before. Thanks everyone for looking into this. Still not sure what the fix is but I will keep reading

Replace your charcoal vapor canister with a VC120 from O'Reilly and check your gas tank for a crack on the top side toward the inside of the truck, about 12" from the front of the tank. If you fill it over 3/4 full, it will run out on the ground.

If you use Ethanol fuel (E10) then you are more likely to get pressure buildup in your tank, especially at elevation.

 

[alia176]

Replace your charcoal vapor canister with a VC120 from O'Reilly and check your gas tank for a crack on the top side toward the inside of the truck, about 12" from the front of the tank. If you fill it over 3/4 full, it will run out on the ground.

If you use Ethanol fuel (E10) then you are more likely to get pressure buildup in your tank, especially at elevation.

There's a hole in this logic. If he has a crack on the tank, then it won't depressurize "for a few seconds" after removing the cap. Right? It should be always in a state of equal pressure with the atmosphere.

 

[BILT4ME]

There's a hole in this logic. If he has a crack on the tank, then it won't depressurize "for a few seconds" after removing the cap. Right? It should be always in a state of equal pressure with the atmosphere.

One would think so. However, even with a verified crack in my tank (it would leak over 3/4 full) mine would still build pressure, at least to get a little "poof" out of the cap when I removed it. I am gueesin the crack was still tight enough that until it heated to a certain point, it was "sealed". After it heated and expanded, and the pressure built a little, it opened up.

I replaced the CC and the problem went away as far as pressurization. I had to replace the tank to get rid of the leak.

So, a hole in the tank does not equal a hole in the logic.....

 

[alia176]

One would think so. However, even with a verified crack in my tank (it would leak over 3/4 full) mine would still build pressure, at least to get a little "poof" out of the cap when I removed it. I am gueesin the crack was still tight enough that until it heated to a certain point, it was "sealed". After it heated and expanded, and the pressure built a little, it opened up.

I replaced the CC and the problem went away as far as pressurization. I had to replace the tank to get rid of the leak.

So, a hole in the tank does not equal a hole in the logic.....

Good explanation, thanks for that!

 

[fj4068]

The ethanol free helps with that problem @ a $.40/gallon or so premium.

Not sure what the deal is with ethanol-free availability generally as it was impossible to find, so I’m happy to see it as a regular option.

Ethanol-free will give a slight decrease in specific fuel consumption, so range and mpg will go up. My very rough tracking has shown approximately 8% differential versus the ethanol blend. Plus it will reduce ethanol-related corrosion concerns. To me, these upsides make the per-gallon ethanol-free premiums worth it.

As far as finding it, I have found the Pure Gas iOS app handy on trips. Ethanol-free gas stations in the U.S. and Canada Unfortunately it's darn near impossible to find in many urban areas--ironically many of the rural areas that benefit from the network of ethanol production subsidies have the ethanol-free fuel.

 

[cruiserdan]

<snip>
ironically many of the rural areas that benefit from the network of ethanol production subsidies have the ethanol-free fuel.

That's because they know first-hand how crappy it is........

 

[cruiserdan]

I am lucky to have a station somewhat local to me that carries straight 91 octane.

 

[84shortyota]

I don't have a charcoal canister. The return line is still there and still receives the waste vapor into the intake manifold for start up burn.

The other line I put a small filter on it and extended the soft line and it vents into the atmosphere.

Is this kosher? Probably not in any emissions jurisdiction that I know of...

I have some venting from the fuel cap on very hot days when I open up to fuel, but after about 6-8 seconds the venting from the gas cap stops.

Take it for what its worth Alvin. I'm not a fuel system expert (or any expert for that matter).

I know this is old, but id love to get rid of my CC. Got a pic of how you routed these lines, namely the return that is getting the waste vapor?

 

[largeone]

Beno's suggestion is fine if you don't have emissions, AND if you don't spend a lot of time driving up above treeline in CO

The worst venting occurs when I am wheeling up really high, and it becomes so bad that it practically gases me out of my truck. So, I'll probably throw on another aftermarket canister next year and call it good for a few more years. The AM canister is not as good as OEM...just like everything else that junky you throw on your truck!