Excessive fuel tank pressure (1 Viewer)

[MaddBaggins]

I didn't either till I read through this thread, worth a try...

That does mean another high altitude run in the near furture.

Well...duh

 

[GeoRoss]

Well...duh

I'm in. Picnic or overnight on mount lemon?

 

[MaddBaggins]

I'm in. Picnic or overnight on mount lemon?

I'll fill up with Techron Supreme and we can take the kids for a picnic saturday

 

[gotmud]

I use 93 octane...no difference. I also have a new gas cap...no difference. I did notice tonight that the line on the bottom of the cc is vented to the atmosphere, not to a fitting near the frame as others have experienced.

From the cc the line goes under the ABS pump

and heads towards the DS inner fender where it vents

 

[MaddBaggins]

same as mine and Ross.

 

[psfpilot]

... BTW, you should not use Redline WW with Toyota Red, causes a sludge throughout the system and has caused some cooling issues for a few folks. HTH.

A touch off-topic here: Are you referring to the regular red Water Wetter or the purple Diesel Water Wetter? I am currently using the diesel version in an effort to reduce warm-weather off-idle/transitional pinging. I was under the impression it was silicate-free and would not react in a negative manner with the silicate-free Toyota Long Life coolant.

 

[cruiserdan]

I wonder if fuel mix has changed to lower the vapor pressure enough to overpower the system? I know that some additives were not run here in the summer because of this, maybe this has changed or they are getting close to the line?

This is a very interesting observation. Just this afternoon I was over at my favorite boat shop and the owner was bitching about the ethanol content of current gasoline. They have been having substantial problems with vapor-lock in Mercury I/O fuel injected engines that are running fuel (the only kind they can find) that is blended with ethanol. The only cure is to drive 165 miles south to get to the one station at Elephant Butte that does not have blended fuel.......

 

[Pskhaat]

This is a very interesting observation...over at my favorite boat shop and the owner was bitching about the ethanol content of current gasoline

On this note on our 5-week southern US "expedition" loaded no doubt to GVWR, 4.10 gears and 315s, we maintain a decent 14-15 mpg highway (and the requisite 10-13mpg city).

Anyway, stopped near the coast in Louisiana and filled up adjacent to a marina with 93 octane E0 (non-blend) fuel. We got 18.5mpg on the same stretch of I10 on cruise control where earlier we got 14.5mpg, identical weather too.

I'm fairly certain that especially during the fuel hikes of last summer, many distributors overblended. Additionally in Phoenix where we're getting such poor volume:energy ratios in 115ºF, it can't help this situation when we drive to cooler altitudes, maybe introducing an abnormally low "A" pressure in the fuel system?

 

[Tools R Us]

This is a very interesting observation. Just this afternoon I was over at my favorite boat shop and the owner was bitching about the ethanol content of current gasoline. They have been having substantial problems with vapor-lock in Mercury I/O fuel injected engines that are running fuel (the only kind they can find) that is blended with ethanol. The only cure is to drive 165 miles south to get to the one station at Elephant Butte that does not have blended fuel.......

Alcohol is one, but there are a few components/additives that can lower the vapor pressure of gas. From some brief research Phoenix area summer fuel is mandated to be 7 psi vapor pressure tested at 100F, but the rest of the state is 9psi.

So we leave with 9 psi fuel, it’s 110F, driving over black asphalt that’s 140F, the A/C is on full bore so the fan output temp is 150F blowing back under the rig. The fuel is pumped through the system and a portion is returned to the tank, used as coolant. After a few hours of driving, how much will this heat the fuel and what will the vapor pressure at that temp be? During our drive we gained altitude, to say 6000 ft and the atmospheric pressure is ~11 psi.

I’m no fuel chemist, so don’t have the answers, but it sounds plausible that this could cause some of the fuel components to vaporize, off gas and overload the system? If so would the effect on system components be permanent or would it be purged out and recover?

 

[sledge916]

Alcohol is one, but there are a few components/additives that can lower the vapor pressure of gas. From some brief research Phoenix area summer fuel is mandated to be 7 psi vapor pressure tested at 100F, but the rest of the state is 9psi.

So we leave with 9 psi fuel, it’s 110F, driving over black asphalt that’s 140F, the A/C is on full bore so the fan output temp is 150F blowing back under the rig. The fuel is pumped through the system and a portion is returned to the tank, used as coolant. After a few hours of driving, how much will this heat the fuel and what will the vapor pressure at that temp be? During our drive we gained altitude, to say 6000 ft and the atmospheric pressure is ~11 psi.

I’m no fuel chemist, so don’t have the answers, but it sounds plausible that this could cause some of the fuel components to vaporize, off gas and overload the system? If so would the effect on system components be permanent or would it be purged out and recover?

tools

I can see your take on this, it seems like a good overview, but mine does it up here in Flag at 7000 feet even when I do not change altitude at all, seems to only do it in hot weather 85 and up, does not get balls soggy hot like it does down there in Phoenix but still does it up here, can actually here it boiling in the tank, = scary!!!!!

Just a thought

Sethro

 

[Tools R Us]

tools

I can see your take on this, it seems like a good overview, but mine does it up here in Flag at 7000 feet even when I do not change altitude at all, seems to only do it in hot weather 85 and up, does not get balls soggy hot like it does down there in Phoenix but still does it up here, can actually here it boiling in the tank, = scary!!!!!

Just a thought

Sethro

Same scenario applies, the raise in altitude is for Mr Baggins/us valley dwellers. If your running 9 psi/100F fuel at say 11 psi atmospheric pressure how much heat does it take to to raise the vapor pressure enough to get significant off gassing?

 

[landtank]

have any of you guys replaced the fuel pump? Maybe that is becoming a bigger heat source as it ages.

 

[GeoRoss]

have any of you guys replaced the fuel pump? Maybe that is becoming a bigger heat source as it ages.

Alvin and I just changed his out on Sunday because we were there and he had a new one (+tank filter) on his shelf. We may find out this weekend if it helps.

 

[sledge916]

have any of you guys replaced the fuel pump? Maybe that is becoming a bigger heat source as it ages.

yup, changed pump, pump sock, and relay

Sethro

 

[sledge916]

Same scenario applies, the raise in altitude is for Mr Baggins/us valley dwellers. If your running 9 psi/100F fuel at say 11 psi atmospheric pressure how much heat does it take to to raise the vapor pressure enough to get significant off gassing?

Hmm I wish I knew the answer to that, I don't know. I sure hope someone figures this out, just a matter of time I guess , this group of people usually do figure things out sooner or later.
Sethro

 

[splitshot]

I'm leaning with Kevin, the additives they are putting in are creating a different flash piont than the system can handle in extreme conditions (or was ever intended to). I thought higher octane would counter act, but Gotmud blew my theory...

 

[MaddBaggins]

If it turns out the fuel additives are the culprit, then the only real choice I'll have is to either drill a vent in the cap or remove the vent line from the cc before I do any trips.

 

[Tools R Us]

If it turns out the fuel additives are the culprit, then the only real choice I'll have is to either drill a vent in the cap or remove the vent line from the cc before I do any trips.

I disagree, would make the “problem” worse.

... I opened the gas cap and it vented for (I kid you not) 10 minutes. …

The only process that I can see causing this is fuel off gassing/boiling, two ways to stop it are; lowering the fuel temp or raising the system pressure. As the fuel temp increases, the vapor pressure is lowered and it starts off gassing. The vapor has more volume than liquid, so pressure goes up. The system is designed to hold pressure, this is a good thing, it raises the boiling point of the fuel, like how the cooling system works. If the pressure is lowered, like you saw by removing the cap, it will boil more.

A vented system would boil off more fuel, more often. Our gas is a cocktail of ingredients, like with any distilling process the ingredient with the lowest vapor pressure will go first. With an open system much more fuel is going to be lost as vapor, at least this way most/some of it is being burned as fuel?

Is this causing a real problem or is it more is a noise/smell issue? Is it setting a code, making the motor run rich, etc? I agree that the system appears to be overtaxed and is operating outside of it's design, so is venting, but is it more than a temporary problem under certain conditions?

 

[a.mus.ed]

I think the worry is that we will do permanent, catastrophic damage to our gas tanks. Both times I experienced this problem, I could hear the gas tank itself reform as the pressure was being let off.

 

[turbocruiser]

I'm inclined to say that something is wrong with the rigs that are having these symptoms OR that people are putting too much gas in the gas tank at fillups ... aka "topping it off." I say that solely based on the fact that despite ascending and descending well over 6k ft in a single run, on almost always a full fuel tank, and on a relatively hot day here ~94 degrees, I don't have this problem. I "vent" for a few short seconds right after removing the gas cap, right after stopping to fill up, right after coming into town on a hot for here day and I almost always am filling up at 1/2 tank (habit). I never smell excess fuel vapors around the canister and I never vent for more than a few short seconds even if I let the tank down to 1/4.

As food for thought the "pressure tests" done as diagnostics are probably hindering the answer if they are done at pressures much higher than the tank generates. IOW if the tank is at say 2 psi vapor pressure and you are testing things at 20 you are going to overcome the obstructions or constrictions or valve malfunctions causing these problems. Its a circular test that returns to zero.

Also, as food for thought, any topping off of the fuel tank causes a comparatively massive volume of fuel to saturate the charcoal canister (massive compared to the slow vapor soak that happens via regular operation). If this has happened and preloaded the charcoal canister the combined effects of that and a hot day, a hot and aging fuel pump perhaps, and a return line that's too close to a heat source / heat sink and, voila, you have high fuel tank vapor pressures. That combined and compounded by assorted chemicals added to the fuel with lower vapor points probably makes this worse. I'd again suggest looking at the return system separately, making sure that there is a smooth running cool running fuel pump, and testing at tank pressures such as 2 to 5 psi. HTH.