Gas tank building excessive pressure & fuel smell. Dangerous for sure! Why does this happen?

[suprarx7nut]

I have seen an aftermarket product for this but never seen/heard of anyone trying on mud on their 100s.

If there was ever an aftermarket mod/thing to attempt messing with OEM environment to resolve I think it has to to with the pressure valve in the tank. Tanks with CC's have a pressure valve that will shut off if too much pressure for CC to handle and then it forces the "secondary system relief point" (in this case our gas caps) to vent....short story the gas cap venting is technically "intended" as the pressure needs to release somewhere. Theres a post/thread out there somewhere that explains all this.

Unfortunately, which is why our thread here exists, the secondary control here isnt safe, sucks to deal with when you are trying to wheel/have fun/camp, and you dont want to worry about blowing yourself/rig up in middle of nowhere!!

Also unfortunately, I dont know enough on how one could override that pressure valve (I could even be getting the terminology wrong on the valve name here) and force the CC to do "more work" and how viable or potentially even worse/more unsafe that may be. But it's something to think about for anyone who may know more on how to approach an aftermarket fix/mod like this.

I think the heat shields are a waste of time and this pressure valve is where the potential silver bullet fix may lie. My gut tells my the valve in overengineered by Toyota to probably shut off sooner than needed to be conservative, as is the case with most of the overbuilt parts on these LC's/LX's!

Interesting point about pressure relief.
I have a couple 3 seater PWC's that have 16gal fuel tanks... and I usually store them completely empty, or completely full.
After noticing the tanks being pressurized over time, or when the skis get hot, I would check on them every few days to open the gas cap and relieve pressure. (these dont have any fancy valves to relieve pressure... and some are known for busting fuel tank seams)

Anyway, my fix for this was to acquire spare gas caps, and put a fitting w/ a 4ft clear hose (so i visually check too) ending with an aluminum one way check valve.
Now, in storage, I never have to worry about a pressurized tank, and if they vent, it would be very little by little. Point is to never let them got to higher pressures.
When I ride, I simply swap the vented gas caps for the original caps. Whether inside a garage, or outdoors, the vented fumes are never at a noticeable level.

-That being said, Im wondering of ways to maybe let the factory gas cap vent safely, (maybe manually controlled)... perhaps a manual valve? when and where we want it to vent.
So... we're not venting next to a campfire, or stove... etc.

-Or Maybe a gas cap w/ one way check valve could work at high altitudes? venting little by little and never getting to the higher pressures? You could even vent the cap, and maybe capture the fumes elsewhere? ... but I'm thinking the factory emmissions checks wont like that... maybe throw a code/CEL? Anyone ever drive w/ gas cap off and get a CEL?

-

I think you guys are on my wavelength when it comes to this problem. I think the purge function is under-utilized in these vehicles and the gas cap safety release is both semi-unsafe and activated too easily. I envision an aftermarket approach to be to add a tank pressure sensor and a relief line that's opened with a pressure switch.

1. Tap into tank - perhaps with a simple T into the line that goes to the CC system.
2. Monitor pressure and find the problematic pressure.
3. Install a pressure switch that triggers an action (12V for instance) just below the problem pressure.
4. Install a valve (basically VSV) that opens when supplied with 12V.
5. Run this vent line either to atmosphere, or ideally into the same line that feeds the engine with CC vapors so the vapors can be safely burned in the engine.

Possible switch: https://www.mscdirect.com/product/details/31043326


My 99 had this problem occur once or twice, but my 06 hasn't had any issues. Once my 06 has this happen, I'll start down this path.

@Joe422 @savirc I just realized my 06 DID have this happen last year. I took a picture of it. Dur. This is why I take pictures, I guess. I'll order up a pressure gauge and experiment with this over the next wheeling season.

 

[Austin Hot Shoe]

We were wheeling in Death Valley this weekend We had driven about 300 miles thus far on asphalt/Titus Canyon(faster speed off road).

We pulled off pavement and did about 20 to 25 minutes of low speed off road. We were coming from approximately an elevation of 250 feet. Temps were in the mid 60s, got up to elevation around 4500 feet. Stopped to take pics and I smelled gas, and saw it venting from gas cap. Visible gas vapors. I plugged in my carsoft and measured engine temp st 185 degrees.

I think my coolant system is in top shape-06' - Temps often 185 to 191.I've yet to install heat shield at fuel lines but I wanted to report this data point as ambient Temps and engine temp were not hot. Fuel filter, fuel pump replaced in last 6 months. Was running 87 octane.

If you can, try non ethanol gas, worked for me once I started using it the Silverton area.

 

[Joe422]

Unfortunately, no practical locations with non-Ethanol gas in So Cali. None close enough to make it feasible, and most listed are for race gas anyway.
Bummer.

On a side note... it seems to me that altitude has a lot to do with this as well.. and makes sense, since gases expand at higher altitude (like your bag of chips).
Would be nice to have a self purging gas cap, used just when wheelin on hot days AND high elevation... and just swap back, maybe at night, or when heading down.

 

[Skidoo]

Yeah I think that would throw a code. I think i saw a post about someone drilling a hole in gas cap but that doesn't seem very "controlled". That's why i was thinking of getting to the valve inside the tank, replacing with newer/bigger valve that allows higher pressure or something. The idea being to direct more fumes/pressure at the CC that's supposed to take those fumes rather than venting from cap at all.

Not so sure you want to bypass feed to CC. Safety and replacement issues. For early models you then have a CC over saturated with gas in a hot engine compartment. Late models have CC behind rear axle, but still can be a hazard. A number of folks have had CC fail and its not cheap, stressing them more may lead to early failure. If you did go down that route, would seem you then have to get the ECU to do more purge cycles to keep things in balance, and that is biting off a lot.

 

[savirc]

I think you guys are on my wavelength when it comes to this problem. I think the purge function is under-utilized in these vehicles and the gas cap safety release is both semi-unsafe and activated too easily. I envision an aftermarket approach to be to add a tank pressure sensor and a relief line that's opened with a pressure switch.

1. Tap into tank - perhaps with a simple T into the line that goes to the CC system.
2. Monitor pressure and find the problematic pressure.
3. Install a pressure switch that triggers an action (12V for instance) just below the problem pressure.
4. Install a valve (basically VSV) that opens when supplied with 12V.
5. Run this vent line either to atmosphere, or ideally into the same line that feeds the engine with CC vapors so the vapors can be safely burned in the engine.

Possible switch: https://www.mscdirect.com/product/details/31043326


My 99 had this problem occur once or twice, but my 06 hasn't had any issues. Once my 06 has this happen, I'll start down this path.

@Joe422 @savirc I just realized my 06 DID have this happen last year. I took a picture of it. Dur. This is why I take pictures, I guess. I'll order up a pressure gauge and experiment with this over the next wheeling season.

I'm willing to test this with that valve you posted there. I replaced my canister with a brand new canister (expensive) and still having issues on my last trip to Big Bend.

I'm due for inspection soon, so I'll probably try it after. I wonder if it will throw CEL?

 

[suprarx7nut]

I'm willing to test this with that valve you posted there. I replaced my canister with a brand new canister (expensive) and still having issues on my last trip to Big Bend.

I'm due for inspection soon, so I'll probably try it after. I wonder if it will throw CEL?

I don't think so, but I guess I can't say 100% because I don't know the test protocol for the purge canister. I think we're safe since my approach would just vent the tank volume pressure upstream of the first component and only down to an empirically determined set pressure, not down to ambient pressure.

I don't know. Lots of unknowns.

Also not sure if you saw my edit, but it turns out I did experience this venting on my 06 last year (as well as my 99 before I sold it). I'm on the lookout for a simple electronic pressure gauge. A boost gauge would work, but ideally I'd find one with a small digital display instead of a big circular gauge. Let me know if you find anything!

 

[NickSonoma]

TL;DR: What are the unintended consequences of heat sink type devices?

I am unqualified to make suggestions(just a bureaucrat), but more than qualified to ask stupid questions:

1) In my experiences, the easiest solutions come down to avoiding a final tipping point (Horrible couple that no one wants to travel with celebrating their 40th, vs. soulmates getting divorced after infidelity.). With this fuel smell problem, it seems like heat/pressure (same thing when it comes to converting liquids to other states/kind of) is our problem, but we don’t know the tipping point temperature or location.

2) COVID has forced me to find my new hobbie of electronics and finally understanding what the parts on a circuit board are. As a result, I now take old electronics apart. I always keep the heat sinks. I use them to cool my coffee quickly to a chuggable temperature. I had a laptop power adapter that I was scared would catch fire one day. Simply placing a heat sink on top of it keeps it at a temp that makes me wonder if it is even plugged in.

3) desoldering has taught me the importance of giving new heat sources a path to escape towards. This can be achieved with something as simple as a copper alligator clip between the component and the heat source.

What I am thinking is, attempting to achieve an unimpressive temperature change that is significant “enough” to diminish the fuel odor. I am imagining a combination of shielding, heat sinks, and even alligator clips/pig tails of copper at areas that lack flat surfaces.

 

[Pskhaat]

I think the big question is, where is the best place to dump heat? I'd throw a few heat sinks at my fuel line (a much better option IMO than shielding) but there's not really a good spot, is there?

 

[NickSonoma]

Without shielding heat sinks would need to be somewhere that the ambient temp is cooler than the fuel line. I have some awesome heat sinks on my bbq-grill called “grill grates” they capture the radiant heat and transfer it to the food through conduction. So heat sinks in the wrong location can become a heat source. Shielding would open up possible locations.

dumb idea 1: Utilize a pc liquid cooling system.

dumb idea 2: snorkel duct directed at fuel system that possibly has heat sinks on it.

 

[Topoguide]

If you can, try non ethanol gas, worked for me once I started using it the Silverton area.

Ethanol in gas (aerated) is definitely a factor. - I was having issues on a trip, hit a state without Ethanol and no problems. The next state that I filled up in had ethanol blend and problem came right back. Everything else was identical, same day, same temps, and similar elevation.

History of my issue: I had a 2000 with absolutely zero issues, but my 2003 has had the issues from the time I bought it in 2008. Same roads/trails during the same time of year with similar temps that I drove in my 2000 will induce this in my 2003. Almost always (maybe always) on Ethanol blend.

The above two items leads me to believe that this is a venting issue of some sort as others have been thinking. The expansion rate of ethanol is greater than gasoline, so the additional expansion from the aerated gas on hot days or at altitude may overwork/overload some sensor or valve. Or maybe even a crack that changes the inputs for the sensor/pot. I don't know I haven't dug into it too much yet... I just try to manage my driving and vent the tank myself at the gas cap. Better that than having it overflow into the canister. - IMO whatever part that causes this is faulty, as many do not have the issue at all... and none of us should have the problem.

If anyone has any updates on finding the issue I would be happy to hear what they have found.

 

[8lifgr8]

The biggest change for me, and I"m not going to say it's "solved" was the pre-cat O2s (I did this along with spark plugs). I don't have any measurements, but I'm assuming my exhaust gas temps went down.

Sure it's been cold outside, but we are using the crappiest blend of Ethanol here in Utah (85 octane even) and I live above 5k feet, have gone to moab and idled a ton, and hardly get any venting out of the tank at a fillup. I'm not talking boiling now, hardly any venting. And when I do get venting, it's just a quick short hiss (like any other car).

So far I've done: VSV, cannister, gas cap, spark plugs, and pre-cat O2s. I bought stuff for a heat shield, but when I went under there my cat already had a factory shield that was bent to deflect away from the fuel lines so I wasn't sure what I was supposed to do with my homemade thing.

Only summer will tell. I've had dangerous levels of boiling and fumes with both non-ethanol and ethanol fuel at high elevation and low elevation. The only common denominator seems to be heat (the boiling almost always happens when idling or crawling in 4-low for extended periods). This last trip to Moab the temperature was 60F, hardly the 90F which caused me to evacuate the vehicle at 4500 feet using regular gas or a mild ethanol blend two years ago, but the tank didn't even hiss when I went to fill up after the trail. That was a small victory.

 

[NickSonoma]

The biggest change for me, and I"m not going to say it's "solved" was the pre-cat O2s (I did this along with spark plugs). I don't have any measurements, but I'm assuming my exhaust gas temps went down.

Sure it's been cold outside, but we are using the crappiest blend of Ethanol here in Utah (85 octane even) and I live above 5k feet, have gone to moab and idled a ton, and hardly get any venting out of the tank at a fillup. I'm not talking boiling now, hardly any venting. And when I do get venting, it's just a quick short hiss (like any other car).

So far I've done: VSV, cannister, gas cap, spark plugs, and pre-cat O2s. I bought stuff for a heat shield, but when I went under there my cat already had a factory shield that was bent to deflect away from the fuel lines so I wasn't sure what I was supposed to do with my homemade thing.

Only summer will tell. I've had dangerous levels of boiling and fumes with both non-ethanol and ethanol fuel at high elevation and low elevation. The only common denominator seems to be heat (the boiling almost always happens when idling or crawling in 4-low for extended periods). This last trip to Moab the temperature was 60F, hardly the 90F which caused me to evacuate the vehicle at 4500 feet using regular gas or a mild ethanol blend two years ago, but the tank didn't even hiss when I went to fill up after the trail. That was a small victory.

If Exhaust Gas Temperature(EGT) is the culprit:

1) Has anyone that installed a less restrictive aftermarket exhaust noticed a difference from the reduction in back pressure?

2) If replacing the 02 sensor made a difference, then this is possibly a software problem. Would applying exhaust heat shield wrap to the exhaust manifold in an effort to reduce heat dissipation trick the ECU into compensating sooner? Obviously you wouldn’t want to do too good of a job with the wrap.

 

[8lifgr8]

If Exhaust Gas Temperature(EGT) is the culprit:

1) Has anyone that installed a less restrictive aftermarket exhaust noticed a difference from the reduction in back pressure?

2) If replacing the 02 sensor made a difference, then this is possibly a software problem. Would applying exhaust heat shield wrap to the exhaust manifold in an effort to reduce heat dissipation trick the ECU into compensating sooner? Obviously you wouldn’t want to do too good of a job with the wrap.

Yeah, doing a cat-back is next on my list. Or maybe a cat-back + mufflers, but then it gets pricey. I don't see any leaks in my system, but I do have some rust, so anything is possible.


The EGT could be a software tuning issue, but based on most of these "boiling" reports on rigs well over 100k (mine didn't start until 120), it would make sense that maybe it's simply a "failing" O2 sensor that the ECU doesn't recognize and doesn't flash a code. It might also be MAF related too, I need to plug in the OBD2 computer and take more real measurements on a test drive.

Based on my driving style, I'm trying to avoid wrapping. I've seen the condition of too many pipes after heat-trace wrapping has been removed, it's a potential corrosion issue as moisture gets trapped between the wrapping and the pipe. I'd rather shield it passively without wrapping it if possible.

Shifting gears to the tank/gas recirc: Is there a valve or seal on the top of the tank that goes to the filler neck that is separate from the charcoal canister? I wonder if something could have failed there? But then the tank wouldn't be able to build pressure.

 

[suprarx7nut]

Yeah, doing a cat-back is next on my list. Or maybe a cat-back + mufflers, but then it gets pricey. I don't see any leaks in my system, but I do have some rust, so anything is possible.


The EGT could be a software tuning issue, but based on most of these "boiling" reports on rigs well over 100k (mine didn't start until 120), it would make sense that maybe it's simply a "failing" O2 sensor that the ECU doesn't recognize and doesn't flash a code. It might also be MAF related too, I need to plug in the OBD2 computer and take more real measurements on a test drive.

Based on my driving style, I'm trying to avoid wrapping. I've seen the condition of too many pipes after heat-trace wrapping has been removed, it's a potential corrosion issue as moisture gets trapped between the wrapping and the pipe. I'd rather shield it passively without wrapping it if possible.

Shifting gears to the tank/gas recirc: Is there a valve or seal on the top of the tank that goes to the filler neck that is separate from the charcoal canister? I wonder if something could have failed there? But then the tank wouldn't be able to build pressure.

I posted a picture of the plumbing of the system a few pages back from the Toyota/Lexus manual. I think that will show what you're wondering.

 

[Topoguide]

The EGT could be a software tuning issue, but based on most of these "boiling" reports on rigs well over 100k (mine didn't start until 120), it would make sense that maybe it's simply a "failing" O2 sensor that the ECU doesn't recognize and doesn't flash a code. It might also be MAF related too, I need to plug in the OBD2 computer and take more real measurements on a test drive.

I bought mine with 76k miles on the clock, I took it above 10k ft at about 80k, which is when I first experienced the boiling problem. I was still getting 19 mpg at that point in time, and my LC had been pretty gently used with only regular maintenance performed. Later I found that it must have been a Friday parts been special... per Land Cruiser standards, as I have had several issues with bad parts and missing bolts from the factory.

I have cleaned the MAF, but never replaced it, however with 19 mpg at the time I struggle to believe it was bad. A failing 02 sensor certainly could be an issue. I may just have to replace mine and post back.

 

[medtro]

A potential solution from post #657.

 

[2001LC]

I bought mine with 76k miles on the clock, I took it above 10k ft at about 80k, which is when I first experienced the boiling problem. I was still getting 19 mpg at that point in time, and my LC had been pretty gently used with only regular maintenance performed. Later I found that it must have been a Friday parts been special... per Land Cruiser standards, as I have had several issues with bad parts and missing bolts from the factory.

I have cleaned the MAF, but never replaced it, however with 19 mpg at the time I struggle to believe it was bad. A failing 02 sensor certainly could be an issue. I may just have to replace mine and post back.

Assuming MPG corrected for tire size.

19 MPG may be indication of running lean. Lean fuel air mixture increases cylinder head temp.

Not likely missing bolts from factory. Finding missing bolts or non OEM parts indicates someone worked on, which is sloppy work at minimum. These are your clues, to past issue(s) someone worked to correct or mods install.

Such low miles on 03, indicates long periods of sitting parked. Which can have bad effects on fuel system components like fuel injectors, fuel pressure regulator, fuel pump. Running fuel system cleaners through fuel system and thorough tuning. Making sure no vacuum leaks or restriction to air intake (including air box and inner fend air tube), would be my first steps.

Coolant system service is so often over looked in low mileage rig. The 03 should have have coolant flushed distilled water (DW)and filled with Toy (red) LL 50/50 mix w/DW, every 2 years. If has not been, consider washing fins of all radiators externally, flush system with BG flush/clean and replacing thermostat and rad cap (OEM).

A bad O2 sensor should set off a DTC/CEL, 99.9% of the time.

 

[archerwolf]

A potential solution from post #657.

Interesting. If this works as a solution, then it means the temperature of the return fuel plays a significant role in causing the boiling and excessive pressures in the fuel tank. The boiling over in my LC100 was solved by wrapping the fuel return lines with reflective heat wrap where the lines pass close to the exhaust -- also lowering the temperature of returning fuel. I'm not saying its the only cause, but trying to lower the temperature of the returning fuel seems like an important solution as long as other maintenance is up to date.

 

[AlpineAccess]

Here's an interesting anecdote not intended to complicate things but just interesting. Just two months ago I got a new Toyota gas cap. Now I get venting noises from the tank when I fill up.

Put old gas cap back in. No venting noises.

 

[Topoguide]

Assuming MPG corrected for tire size. - It was the stock tire size, and hand calculated.

19 MPG may be indication of running lean. Lean fuel air mixture increases cylinder head temp. - Ran at 17-19 mpg for several years (at 65 or below) with the only noticeable issue being the gas pressure on "oxygenated" gas. Some of us were fortunate enough to see mileage that high with a stock truck and an easy foot, but increasing tire size/weight and other things brought that down.

Not likely missing bolts from factory. Finding missing bolts or non OEM parts indicates someone worked on, which is sloppy work at minimum. These are your clues, to past issue(s) someone worked to correct or mods install. - Yes, believe it or not missing bolts from the factory; this was in the back of the V discovered when replacing the starter, not a huge deal but definitely missing and no one was there before me. No non-OEM parts at all. Did have a rear brake caliper that I finally realized had a defect from the factory, had a master cylinder that had scoring inside at the lip that I had to correct to rebuild, etc. Like I said a Friday afternoon parts bin truck... per Land Cruiser standards.

Such low miles on 03, indicates long periods of sitting parked. Which can have bad effects on fuel system components like fuel injectors, fuel pressure regulator, fuel pump. Running fuel system cleaners through fuel system and thorough tuning. Making sure no vacuum leaks or restriction to air intake (including air box and inner fend air tube), would be my first steps. - Low miles? Average of $15k a year is low enough to cause all those issues? I think not. We drive it quite a bit and it now has over 220 k

Coolant system service is so often over looked in low mileage rig. The 03 should have have coolant flushed distilled water (DW)and filled with Toy (red) LL 50/50 mix w/DW, every 2 years. If has not been, consider washing fins of all radiators externally, flush system with BG flush/clean and replacing thermostat and rad cap (OEM). - Right, that is why I regularly change fluids on it.

A bad O2 sensor should set off a DTC/CEL, 99.9% of the time. - Normally yes, but we are trying to diagnose a very specific issue that some of us have, and no one has definitively been able to solve yet. At the mileage my truck is at coupled with another issue I am repairing I am willing to throw a few bucks at it.

Now back to our regular scheduled discussion about the problem of the boiling gas / gas venting issue.