Gas Erupts from Tank

[Ice Man]

I have an 05 FJR with about 12k miles. I went riding with 3 friends yesterday -- it was 60 degrees & I filled my tank at the local Shell station. At 125 miles into the ride, my friends needed gas so I decided to fill my tank as well -- still had half tank -- it was probably 85 to 90 degrees. When I opened the tank, there was a "giant sucking sound" quickly followed by a column of gas gushing out of the tank -- about 2 feet above the tank -- fortunately no fire. Everything about the morning had been normal and this has never happened before. I read about this problem with an FJR that had been filled at near sea level, was transported to higher elevation and upon opening the tank, same thing happened. My ride did not involve any significant elevation change -- only about a 25 to 30 degree change in air temp.

Anyone else experienced this problem?

P.S. I did a search and could not find any mention of this.

 

[wheatonFJR]

Sounds like the breather tube is clogged from what others have posted before...

...waiting for ionbeam or others to post with the real answer.

 

[twowheelnut]

Yep, this has been reported a few times. IIRC, bounce had the best explanation of the symptom and the cure, as well. You may wanna ping him.

 

[FJRBluesman]

Great balls of fire Batman!! That was a close one!!

Seriously, I have never heard of that but it's possible as stated with a clogged breather tube. I'm waiting to see the fix too.

In the future you may want to open the gas cap slowly and let the pressure equalize then you won't get that sudden vacuum rush of air and displacement of fuel.

Good luck.

 

[Bounce]

Clean your filler neck and check to make sure the "orange thing" is lined up properly and clean. This should be part of your routine mantenance schedule:

https://www.fjr-tips.org/maint/ff/ff.html

Another tip is to get under your bike, find the 2 drain hoses, and clip them so they have a 45° angle - / (long end toward the front and short end toward the back of the bike). This helps slow down the accumulation of crud in the ends of the drain lines by placing the longer side toward the front of the bike so it can act as a "shield" for the opening. Also, get under the bike and clean the ends of the drain hoses semi-annually unless you think it should be done more frequently.

 

[FJRBluesman]

Excellent post Bounce! Thanks.

 

[artistonFJR]

Holy crap! Just the visual I get from that is scary! Gas-geysers... not how I want to end a bike ride.

Thanks bounce... my bike is new, but that will always be a "must check" for me now.

C

 

[conwest]

...it`s also a good idea to point yer air nozzle into the orange ringed airway every now and then. U can easily do this with the other hand held at the bottom of the hose. U feel air coming outta there and yer good to go! :assassin:

 

[dbvolfan]

My '05 did that following a service visit. Scared the crap out of me...even worse, it was August so the heat made the damn thing vent like a geyser.

Lifted the tank and found that when they had lowered the fuel tank they had completely crimped the fuel vent. Straightend it out and havent had any problems since then.

 

[ndivita]

Happened to me on my 2005 FJR in 2006 after riding flat out in 100 degree heat for about a half hour, when the fuel was below a quarter tank. I had stopped for the day, and was gassing up before finding a hotel. Upon opening the gas cap and adding new fuel, it spurted up like Old Faithful. Scared the living daylights out of me. That was BEFORE I added Smitty's heat shield fix. Has never happened since, despite identical conditions. I am sure someone on this board will correct me if I am wrong, but I believe fuel can actually boil under certain conditions. The heat shield, to my way of thinking, now insulates the tank sufficiently to prevent this from happening. Still, I always let the tank fumes vent a few seconds before adding new fuel on a really hot day. My bike now has 20,000 miles and runs like the Starship Enterprise. If you have not done so, add the heat shield blanket fix to your 2005 model.

 

[dgfella]

Yep, it is your breather hoses and it scares the crap out of you when it happens.

I'd lift up the tank and check the underside. Several tanks have been crushed by fuel pump vacuum. If you've got the extended warranty, you may be able to get a replacement.

 

[collett]

You are right ndivita, gas will boil. We had our Grizzly 660 ATV's boil gas in the tank all the time when it was hot out. We fixed it by cutting out holes in the side engine covers so the engine would vent better, but sitting on the seat hearing (and seeing) the gas boiling in the tank all the time was really hard to get used to.

 

[Fred W]

OK, I guess I see that the theory is that the vent hose is getting clogged or kinked and we are pulling a vacuum in the tank. Obviously this is a problem to be avoided as it would result in an imploded tank.

But how is this related to the temperature (as some have suggested) and how does this cause the "Gasoline Geyser" in the OP? He says he heard a "sucking" noise when the cap was opened followed by gushing fuel. Is the sudden increase in pressure inside the tank somehow precipitating a sudden boiling of the fuel? I don't think that makes any sense since liquids have a higher boiling point with increased pressure.

It must really be that the fuel has already been boiling in the tank, and the tank is highly pressurized. The noise heard was actually vapors escaping outward (not sucking). The sudden de-pressurization would then lower the boiling point and precipitate increased boiling resulting in the high test geyser.

I suppose that if your vent is clogged you could get either/both hazards, over and under pressurization as temps varied...

 

[Bounce]

in an efi system, the tank is pressurized. there are safeties to keep it from being over pressured. if these get clogged or kinked, then you lose those safeties.

 

[saread]

OK, I guess I see that the theory is that the vent hose is getting clogged or kinked and we are pulling a vacuum in the tank. Obviously this is a problem to be avoided as it would result in an imploded tank.
But how is this related to the temperature (as some have suggested) and how does this cause the "Gasoline Geyser" in the OP? He says he heard a "sucking" noise when the cap was opened followed by gushing fuel. Is the sudden increase in pressure inside the tank somehow precipitating a sudden boiling of the fuel? I don't think that makes any sense since liquids have a higher boiling point with increased pressure.

It must really be that the fuel has already been boiling in the tank, and the tank is highly pressurized. The noise heard was actually vapors escaping outward (not sucking). The sudden de-pressurization would then lower the boiling point and precipitate increased boiling resulting in the high test geyser.

I suppose that if your vent is clogged you could get either/both hazards, over and under pressurization as temps varied...

You're almost exactly right.

It's chemistry and physics. Gasoline (and its constituents) are very volatile. Meaning that they vaporize easily, especially when heated. Gasoline will boil anywhere from 100 deg. to 400 deg. depending on formulation; e.g., benzene will boil at 176 deg. However, boiling point is also dependent upon pressure. The higher the pressure, the higher the boiling point. This is why water boils at less than 212 deg. at altitude. So, if we close the vents on a gas tank, the only release of pressure is through the fuel being used by the engine. When we add engine heat and warm weather to a gas tank, we can create more pressure than we can relieve. So, although we may exceed the temperature at which the gasoline would otherwise boil at atmospheric pressure, it doesn't boil because the pressure inside the tank raises the boiling point temp. Now, we bring our steed to the fueling station on this hot day and we pop the tank - we release the internal pressure and the gasoline is still very hot, BLAM some of the hot gasoline flashes (remember lower pressure = lower boiling point) to vapor and suddenly there's a big change in volume and a whole bunch of stuff that needs to leave the tank all at once. Now you have a gasoline geyser. This is virutally identical to the mechanism that makes Old Faithful work at Yellowstone (instead of a gas cap, it's mud that blocks the channel).

The moral of this story is: "Check your vents."

 

[Fred W]

Hmmm... Okay. Can you tell us why it is important for the tank to be pressurized? And where does the positive pressure come from?

I can understand why you wouldn't want a vacuum, but why would you need a positive pressure? Do you suppose that it is intentional to increase the boiling point of the fuel?

I just did some poking around on my tank. There is apparently some kind of a check-valve inside the Gas Cap vent. Putting a piece of rubber vacuum hose over the small hole in the edge of the cap (the one that mates with the red rubber o-ring) I can easily blow air through the cap, which would be the direction of air coming up the vent tube and into the gas tank. But if I suck on the same tube I feel a much higher resistance to airflow. Meaning that a positive pressure in the tank would not be as readily relieved.

I then put my MityVac on the hose and when the end was flush against the flat side of the cap adjacent to the vent hole I was able to draw a decent vacuum. Then when I move it over the vent hole the vacuum was relieved slowly. So, maybe it is a pressure relief valve of some kind? Unfortunately the parts list does not show the cap disassembled.

Putting my rubber mouth-hose on the red rubber o-ring seal I can get air to easily move in both directions, so my vent line is apparently clear.

BTW, as it has been suggested elsewhere, it appears the red rubber o-ring serves no real purpose in life other than to isolate the fuel tank vent pipe from the overflow pipe. Not sure why that was particularly important from a design aspect. If the red ring is gone missing the venting and overflow would just occur through both tubes.

 

[saread]

I don't think it matters that the tank be pressurized, as long as it there isn't an excessive vacuum. The fuel pump and relief valving in an FI system will regulate the necessary fuel system pressure. Too much vacuum may make the fuel pump act up. The reason there is positive pressure in most fuel tanks is for emissions. There is a typically a check valve in tank vents (the cap usually) that controls vapor escaping from the tank. This is an emissions requirement (remember the activated carbon filters on older cars in the fuel venting system). Pressure build up is from gasoline vapor pressure building up faster than pressure relief can happen either by the check valve in the cap or by fuel consumption. If you live in Seattle (or Cali or anyplace that checks emissions) one of the things they check on your car is the fuel cap. They aren't checking its ability to allow air in - they're checking it's abilty to keep vapor in. Of course, you don't want a valve so strong that it will allow unlimited pressure - but you can get quite a bit of pressure if there's enough energy going into the fuel to allow it to volatilize faster than the volume of gas being created can be vented. Here in Seattle, we don't usually have this problem, but I've had some pretty big CHUFFS come off of cars when I've popped the gas cap in the southwest - no geysers though.

 

[Fred W]

There is a typically a check valve in tank vents (the cap usually) that controls vapor escaping from the tank. This is an emissions requirement (remember the activated carbon filters on older cars in the fuel venting system).

Bingo.

While most of these bikes don't have a charcoal cannister, the CA models do, and I believe that the gas caps are the same p/n.

I'm thinking that the check valve could get gummed up as easily as the vent tube. Either could be the root cause of the sudden decrease in tank pressure that then results in the "gas geyser".

I should probably take a cap apart and see what the heck they have in there. Enquiring minds, and all that...

Fred, You haven't been paying attention to the past posts in this thread have you?
There's a link to a page that IDs that orange "pressure valve" in msg #5.

Actually I have been, Mark. The red rubber o-ring is misidentified on your web site article as being the "check valve". In reality it's just a seal between the cap assembly (where the "check valve" is really located) and the vent tube below.

But it does have some good pictures of the whole deal...

 

[Bounce]

good point. i need to update the description. it's been a while and chuck's description of drilling out the cap has come out since then.

--update now on line--

https://www.fjr-tips.org/maint/ff/ff.html