It happened to me, gas venting issue

[Brian894X4]

So, I've read several threads over the last couple of years of people who smelled gas and then removed their gas cap to have it vent and boil for several minutes or longer. I didn't really pay much attention as this has never happened to me...until now.

Was on a trip to Eastern Oregon. Weather was not particularly hot...maybe in the 70s or low 80s. After doing a bit of a climb on some dirt mine roads...maybe a few thousand feet... the rig was parked idling for a while, when I noticed a distinct faint smell of gas, but couldn't really figure out where it was coming from. It was clearly from my rig, but was not obvious where. Not from the engine compartment, not from the underside or anywhere near the gas tank. Maybe...around the gas fill, but not sure.

Remember what I read on here, I released the gas cap and a huge whoose of fumes came roaring out of the filler and it vented for about a good 1 or 2 minutes. I could even hear what sounded like boiling in the tank, as mentioned before by others.

The only difference is that others have mentioned it venting for a long time. Mine vented pretty quickly, although I started by slowly releasing the cap and then fully released the cap about 10 seconds later. Maybe others are only slowly releasing the cap and letting it vent without fully removing it.

So...any concensous on what's going on here? Haven't had it happen since and I've driven up and down roads and changed elevations since.

Smelling that gas scared the crap out of me by the way. Out in the freaking middle of nowhere, I was having visions of Land Cruiser barbecue. So, I'd like to solve the issue.

 

[SBFJ60FIG]

Time to mount a fire extinguisher eh? Had one in my 60, but that seemed logical with a small block and cobbled together fuel injection, engine wiring, a small block, etc.

I'm curious too about the venting...my tank always vents pretty hard when removing the filler cap with a nearly empty tank...seems normal though, no boiling sound or severe air rushing going on.

 

[Ihasfip]

Well I got the same thing the other day. With no change in elevation. Searched and read lots of threads, but no one seemed to have an answer. I hope someone figures this out. Its kinda scary, and I would rather not be riding around on a ticking time bomb.

D

 

[gotmud]

Living in Phoenix, this is an issue I am dealing with on a daily basis during the summer months. This past weekend, I spent some time in southern AZ where the elevation is around 5000' and the temps are much cooler than here in the valley. Didn't have a single issue with pressure build up or gas boiling off when I removed the gas cap. Here are a couple of oberservations:

Had "Phoenix" gas when I arrived in Sierra Vista (5000'), removed cap to fill up an no excess pressure. Temp was around 85

Went through a tank of "Sierra Vista" gas and filled up before my trip back to Phoenix. No pressure when filling up. Temp was still around 85

Topped off fuel in Tucson ($.45/gallon less than Phoenix ), no pressure build up (2500') Temp around 75

Stopped in Phoenix around 11am, temp was 100. Could smell gas fumes when I got out. Opened up the gas cap and fuel boiled off for about 30 seconds. Tank was 1/4 full.

I try to keep the tank full during the summer months. This helps avoid pressure build up.

Charcoal canister is new.

 

[NKP Garage]

This problem happens on any vehicle and is more of a problem when you run the gas low all the time. It is actually bad for the fuel pump as well.

What is basically happening in most cases is that the fuel level starts to drop below the actual fuel pump itself. The problem here is that the fuel pump actually uses the fuel in the gas tank as a cooling mechanism. When there is less and less fuel in the tank, the fuel starts absorbing as much heat as it can and after a certain point it is simply heat soaked. When the tank is low on fuel (below the fuel pump) that duplicates the issue because there is not enough fuel surrounding the fuel pump to actually help cool it down. On top of that the fact that the fuel heats up quite a bit when going through the hot fuel rail and then returning to the fuel tank hotter than when it left doesn't help either.

The only real solution for this is to add a fuel cooler. A fuel cooler is a cheap and easy modification, but most people see it as a modification that shows no "performance" benefit. There's been many debates over the years on various forums regarding the issue of performance and fuel temperatures. I for one believe that there is a performance increase when the fuel is at a cooler temperature. Up for debate I guess till proof is shown.

 

[john_eckels]

The charcoal cannister is supposed to vent the excess pressure. You may want to check to see if it is plugged.

 

[CJF]

The charcoal cannister is supposed to vent the excess pressure. You may want to check to see if it is plugged.

That is exactly where I would start looking. There are simple tests for it in the FSM.

Curtis

 

[Brian894X4]

Well, Gotmud mentioned that his canister is new and no change. But I'll definately check. I have a couple of shot in the dark theories. But first, my tank was never anywhere near empty. In fact it was about half full when this happened.

If it's a matter of the fuel getting too hot, then trying to imagine what could cause this, the only thing I can come up with is that maybe it gets hot in the fuel rail and the return fuel is heating up the fuel in the tank?

In doing some research, the boiling point of gasoline is pretty wide depending on a number of factors, not the least of which is octane level, additives and elevation.

The one thing I remember is that I had just filled it earlier in the day with cheap 87 octane fuel at a remote fueling station that probably did not have the highest quality gas. I normally run premium fuel as it helps with the pinging issues, but couldn't get it that day.

Could the cheaper lower octane gas have a relatively low boiling point, so the combination of slow speed driving (going up these steep mine roads, lots of power and heat generated, but not much airflow) and increase in elevation (which lowers boiling points) all contributed?

The only thing that I'm a little confused on is that the fuel system is under a different pressure than the outside air, so I'm not sure how that affects the system.

Could using a ton of fuel in a short period of time in slow speed driving, contribute as the fuel canister gets over saturated from rich fuel vapors? I recall reading that 1FZ tends to run somewhat rich to keep the engine cool, which I think is one reason for the relatively poor gas mileage. Being an engine designed for harsh 3rd world conditions, engine survivability is more important than fuel economy or power.

In the end, I can't imagine this is normal, even with bad gas. Toyota designed the 1FZ specificly to run on 3rd world gas, including lower octane poor quality fuels. But the U.S. 1FZ does have some emissions equipment not required on overseas vehicles that might hinder the overall fuel system design.

Guess I need to do a little more research.

 

[NKP Garage]

Well, Gotmud mentioned that his canister is new and no change. But I'll definately check. I have a couple of shot in the dark theories. But first, my tank was never anywhere near empty. In fact it was about half full when this happened.

If it's a matter of the fuel getting too hot, then trying to imagine what could cause this, the only thing I can come up with is that maybe it gets hot in the fuel rail and the return fuel is heating up the fuel in the tank?

In doing some research, the boiling point of gasoline is pretty wide depending on a number of factors, not the least of which is octane level, additives and elevation.

The one thing I remember is that I had just filled it earlier in the day with cheap 87 octane fuel at a remote fueling station that probably did not have the highest quality gas. I normally run premium fuel as it helps with the pinging issues, but couldn't get it that day.

Could the cheaper lower octane gas have a relatively low boiling point, so the combination of slow speed driving (going up these steep mine roads, lots of power and heat generated, but not much airflow) and increase in elevation (which lowers boiling points) all contributed?

The only thing that I'm a little confused on is that the fuel system is under a different pressure than the outside air, so I'm not sure how that affects the system.

In the end, I can't imagine this is normal, even with bad gas. Toyota designed the 1FZ specificly to run on 3rd world gas, including lower octane poor quality fuels. But the U.S. 1FZ does have some emissions equipment not required on overseas vehicles that might hinder the overall fuel system design.

Guess I need to do a little more research.

Read my post...

How much gas is in the tank when you guys see/notice it boiling?

 

[landtank]

I was asked to look at a truck where gas was leaking from an empty aux gas tank. Sure enough when it started to leak I pulled the gas cap and once fully vented the leak stopped.

I then replaced the cap and gave it some time. About an hour later the leak again appeared. This time I opened the hood and removed the hose to the "tank" nipple on the charcoal canister.

There was a rush of fumes and once subsided the leak stopped. I took this to mean that the vent line from the gas tank was clear and able to vent the fumes fast enough to keep the PSI down in the tank.

So we replaced the charcoal canister and everything is fine.

I did try and blow through the original canister with no luck while I could blow through the new one with only slight resistance.

FWIW, I almost managed 2 PSI with my lungs according to a gauge. I've read that 2 psi is about the most pressure you should build in the tanks. So if you can't blow any air through the CC it's probably bad.

 

[UCBerzerkeley]

Read my post...

How much gas is in the tank when you guys see/notice it boiling?

He answered it in the first line. About half a tank of predicted poor quality 87

 

[UCBerzerkeley]

I was asked to look at a truck where gas was leaking from an empty aux gas tank. Sure enough when it started to leak I pulled the gas cap and once fully vented the leak stopped.

I then replaced the cap and gave it some time. About an hour later the leak again appeared. This time I opened the hood and removed the hose to the "tank" nipple on the charcoal canister.

There was a rush of fumes and once subsided the leak stopped. I took this to mean that the vent line from the gas tank was clear and able to vent the fumes fast enough to keep the PSI down in the tank.

So we replaced the charcoal canister and everything is fine.

I did try and blow through the original canister with no luck while I could blow through the new one with only slight resistance.

FWIW, I almost managed 2 PSI with my lungs according to a gauge. I've read that 2 psi is about the most pressure you should build in the tanks. So if you can't blow any air through the CC it's probably bad.

In another long thread on this topic, several people replaced their canisters and the problem continued IIRC

 

[Filmpros]

Yes, this was my truck Landtank is talking about...it has not been an issue since the Charcol Canister was replaced.

Rich

 

[NKP Garage]

If replacing the charcoal canister is not solving the issue, problem still points to the fuel pump and heat. Check your fuel filter and the "sock" filter on the fuel pump assembly itself.

Worst case there are many people that simply remove their charcoal canister. Personally I'd try to keep it and fix the issue, but if it's the cause of the problem in your particular case, it can be removed and just reroute the hoses.

 

[landtank]

the charcoal canister is not the end of the line for the vent. There is a line that comes out the bottom of the canister and either purges to atmosphere or connects to a tube mounted to the frame where it purges to inside the frame.

This is no different than any other problem where a systematic diagnostic routine should locate the issue. Swapping out parts can be expensive and yield no results.

If you are smelling gas try disconnecting that line to the CC and see if the pressure in the tank is releaved. If it isn't then there is an issue between the tank and the CC and if it does releave the pressure than the problem is with the CC or further out.

 

[gotmud]

As I mentioned earlier in this thread and the "other" thread. I have replaced both the CC and associated plumbing from the tank to the engine when I rebuilt my engine earlier this year. My CC is good, not just because it is new, but because it checks out OK. Ditto for the TVV, VCV's and both check valves. What I believe is happening in MY case, has to do with:

blend of gas used here in Phoenix
- the additives in the fuel here have significantly lowered the boiling point

heat here in Phoenix
- this kinda goes without saying

The combination of recycled fuel (which picks up heat under the hood before it returns to the tank) and the radiated heat from the road build up more pressure in the tank than the CC is capable of processing, thus the excessive pressure build up.

I would guess this is similar to what others are experiencing. Perhaps the fuel alone could be the issue for those of you who don't live in a furnace.

 

[Ebag333]

The combination of recycled fuel (which picks up heat under the hood before it returns to the tank) and the radiated heat from the road build up more pressure in the tank than the CC is capable of processing, thus the excessive pressure build up.

What about installing something like:
Moroso 65125 - Moroso Super Cool Cans - Overview - SummitRacing.com


Anyone try this?

 

[Tenzig Norgay]

Someone squirted carb cleaner(or something) down the line from the CC towards the tank. IIRC, his theory was that there is a check valve somewhere along the line that gets clogged/blocked, leading to the excess pressure. Clean the line and valve, no pressure build up.

Makes sense, if there was no check valve, gas would flood the CC everytime we went down a steep hill with a full tank....maybe....anyways. He cleaned the line and said it fixed the prob. Haven't heard the long term prognosis. Who were you and did it solve the prob?

It was the jeeper guy who thought he figured it out. The thread was "Excessive fuel tank pressure". Only 4 pages long, but the last post, or second to last describes his solution, and nothing since.

 

[RavenTai]

There is a check valve in the evap system but not on the tank->cc side, the cheak valve is is the purge portion and should not have any effect. schematic shows open line from tank to CC.

Mine has often has pressure in the tank at refill time, sometimes surprising amount of fumes rush out, have had previous vehicles do same, never thought much of it.

I doubt you had boiling fuel, I have had faint noise from the evap system when when standing near the truck engine off, liquid fuel got caught at a low spot in the vent line. makes somewhat like a gurgling noise especially when the tank is pressurized, I could see how it could sound like boiling fuel. fixed it by removing gas cap and blowing in the "from tank" line at the CC. the air pushed the fuel back into the tank clearing the line and stopping the gurgling noise.

 

[gotmud]

...I doubt you had boiling fuel...

Actually, that is exactly what is happening. Quoting Wiki "At atmospheric pressure, the boiling point of gasoline is between 100 and 400 oF. A primary cause of this variance is the various additives in the gasoline from different refiners designed to meet different octane requirements."

If you read my earlier post, you'll see that I had no problems on my recent trip until I got back to Phoenix, where the temp was >100F.

This morning, I popped the gas cap before leaving for work. The temp in my garage was 80F. -No fumes/pressure with about 1/4 tank of gas. At lunch when I go back out, I'm sure if I pop the gas cap again, it will release fumes. I park in an underground garage, but the temps will be the same as outside. Should be around 105 here today.