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

[Pskhaat]

I'd sure wire up a battery +volts set up to the pump itself with a switch before I sold the thing.

I didn't test resistance, but I had 12VDC (12.something but don't recall exact) when I tested during pump replacement. Assume it would be a good 13.8VDC during operations. I am well aware that does not measure current and subsequent heat-induced problems with a load sink.

My 07 rocks always starts up immediately and fuel no longer boils. Sorry you didn't follow my tips.
If your tank doesn't leak then the pressure increases with heat = impossible to boil.
Everyone who has boiling fuel has a leaking gas tank, fact.

If I "vent" the tank from the cap, yes there is positive pressure in the tank. FWIW, I've never had fuel boil out at me like I've had in other vehicles. I'm not sure what tips I have not followed (if that was directed at me?)

Have you done a cooling system overhaul? Do you hear exhaust more than you should in the wheel wells?

Yes, I replaced radiator sometime ago (late 2018 IIRC), and a distilled flush with refill September 2020. No signs of sediment, fluid loss, etc. To be fair our >560 mile dirt tour last October I had zero (re)start issues.

Maybe I missed a few posts about the exhaust sound??

 

[suprarx7nut]

Yes, I replaced radiator sometime ago (late 2018 IIRC), and a distilled flush with refill September 2020. No signs of sediment, fluid loss, etc. To be fair our >560 mile dirt tour last October I had zero (re)start issues.

Maybe I missed a few posts about the exhaust sound??

New radiator have all the foam?

Exhaust: On my own 06LX, I believe I have exhaust leaks on the manifold (either at the head or right after header). I believe these leaks add to heat in the engine bay and therefore fuel lines/fuel. That's why I ask.

Also, FWIW, I think there are two separate issues being discussed here. They may have some overlapping causes and fixes, but they're different problems and don't necessarily occur together.

Fuel Vapor Purge failure: fuel gushing out of the filler neck because the tank is over-pressurized. Potentially deadly and known to literally burn 100's to the ground.
Hot Start Failure: Car intermittently fails to start when hot and starts again once cool.

 

[Pskhaat]

Fuel Vapor Purge failure: fuel gushing out of the filler neck because the tank is over-pressurized. Potentially deadly and known to literally burn 100's to the ground.
Hot Start Failure: Car intermittently fails to start when hot and starts again once cool.

Not just 100s as 80s have had similar boiling and pressure problems. "Hot Start" can be an actual vapor lock issue which cannot be distinguished as (unless someone tells me otherwise) I have fuel vapor (not in fluid state) in my system which limits fuel movement in regulator.

Though I do NOT have the filler neck squirt problem, has the problem been identified there?

 

[suprarx7nut]

Though I do NOT have the filler neck squirt problem, has the problem been identified there?

Depends who you ask, haha. It's gotten oddly contentious.

I think a few workarounds have been identified to reduce temps and prevent safety pressure reliefs from activating, but not a sole root cause which can be corrected.

The purge system *should* prevent gas tank pressure from building enough to activate the safety relief, but seems unable to do so for many people in either hot or high altitude situations.

My continued belief is that the purge system is prone to blockage or is simply undersized and cannot evacuate enough vapor to prevent an over-pressure situation. Modern ethanol blend gasoline seems to exacerbate the problem, but the problem remains with ethanol free gasoline for plenty of people.

I had it occur last year in my 06 and had experienced it before in my 99. Both times were relatively hot (85F+ I think) and I was in and out of high elevations (10,000 ft+).

 

[lehiguy]

I'm in this boat. Had a nerve racking no-start in Vegas yesterday, car showed 114 degrees. My gas cap is new, my fuel pump is new. Heavy gas vapors outside the vehicle and then the vapor lock. One odd symptom, I never have positive tank pressure, so something is out of whack. Thinking new charcoal canister with the attached valve. Tired of chasing it.

 

[suprarx7nut]

I'm in this boat. Had a nerve racking no-start in Vegas yesterday, car showed 114 degrees. My gas cap is new, my fuel pump is new. Heavy gas vapors outside the vehicle and then the vapor lock. One odd symptom, I never have positive tank pressure, so something is out of whack. Thinking new charcoal canister with the attached valve. Tired of chasing it.

Was this when the car was warmed up from a previous trip? IE hot start?

Did it start again after a brief waiting period?

FWIW, I wouldn't expect a new charcoal canister to help the no start situation.

 

[lehiguy]

it was thoroughly heat soaked and then sat for 10 minutes soaking up the Las Vegas sun, pointed slightly uphill. There was an overwhelming smell of gas from the back of the car. It started and moved about 100 feet and pooped out. It did recover after I bled some pressure from the fuel filter. I mostly wanted to see if there was gas present. That seemed to help.

 

[tucker74]

I bought some of this and wrapped all the fuel lines around my DS cat to try and solve this, taking a ~2000 mi trip in a few weeks up to the mountains and will report back if it helps.

Heat Shielding Sleeve, Silver

Ensure the safety of critical lines and wiring with the Mishimoto Heat Shielding Sleeve. Our sleeves are constructed from a robust combination of aluminum and fiberglass for optimal protection against up to 1100°F of continuous and 500°F of direct heat. Our sleeves also feature hook and loop...

www.mishimoto.com

Tucker

 

[J1000]

I didn't test resistance, but I had 12VDC (12.something but don't recall exact) when I tested during pump replacement. Assume it would be a good 13.8VDC during operations. I am well aware that does not measure current and subsequent heat-induced problems with a load sink.




If I "vent" the tank from the cap, yes there is positive pressure in the tank. FWIW, I've never had fuel boil out at me like I've had in other vehicles. I'm not sure what tips I have not followed (if that was directed at me?)



Yes, I replaced radiator sometime ago (late 2018 IIRC), and a distilled flush with refill September 2020. No signs of sediment, fluid loss, etc. To be fair our >560 mile dirt tour last October I had zero (re)start issues.

Maybe I missed a few posts about the exhaust sound??

Is your fuel actually boiling? ie: you can hear a rolling boil like a pot on the stove? Or are you just experiencing other symptoms?

 

[lehiguy]

I rerouted the return line off the engine and up across the firewall. I also put heat wrap around the return line as far as I could. It still happened. I know there is a relationship between the gas fumes, the no-start and the apparently wimpy charcoal canister. No other Toyota of mine has EVER exhibited this behavior. I am curious if it's possible to upgrade the whole canister to one from a second gen Tundra. Anybody own one of these that could have a look see? Do they have these problems in the outback? Do the Aussie versions have cats? I start to wonder about the wisdom of having something that runs at 700 degrees right next to the fuel lines. There's my rant for the day...

 

[thebeedeegee]

It seems pretty exclusive to 06-07 LC/LX's.

My 99 did it to me this past week at only around 800 ft of elevation. Not full on vapor lock, but could smell fuel and it vented for about 15 min

 

[Joe422]

I added a heat shield between the catalytic converter and the fuel lines today. I also wrapped as much of the fuel and vapor lines as I could in the engine compartment. Tomorrow I’ll pull the old exhaust and see what I can do about a shield between the muffler and that gas tank. Then, install the Borla exhaust. The muffler is significantly skinnier than stock, so that should help. Replace the charcoal filter, then after that, I’ll tackle the radiator and see if I can get it running a bit cooler.

My daughter is stealing it for a 3 week trip in July and I’ll be hauling the whole fam to Moab in September. I hope this works, cuz I don’t want to have to stress it!

Nice... looking fwd to hearing reviews on what helps~

 

[DTC72]

Nice... looking fwd to hearing reviews on what helps~

Scroll up several pages and read the post from J100 about the top three things that helped.

 

[jerryb]

Some of what he says is true, 20 degrees F over ambient rail temp is an accurate number in almost all instances. I've seen 30 -35 on occasion, all normal and doesn't really matter up to a certain unknown temp higher than 160. What matters is the ability of the tank to shed heat. If it doesn't you're F ed.
Your actual liquid temp in the rail goes up dramatically after shutdown. Upon start up it cools back down exponentially faster.
The higher the tank temp the easier it is for that volume of fluid to equalize with the rail or block temp.
We all know this I hope. I hope we also know that there is only one way the fuel tanks get pressurized with a gas(air)
Ignore the pressure volume temp thing and focus on the liquid process.

Personally I find It silly to think that fuel 15 years ago is the same as it is today and should power all vehicles as it did when they were new.
It will get worse year after year.
Controlling the tank temp is the goal. Seems pretty simple to me, and here we got 30 some pages of stuff.

 

[hoser]

My 99 did it to me this past week at only around 800 ft of elevation. Not full on vapor lock, but could smell fuel and it vented for about 15 min

When I say “it,” I mean a no start condition. If your’s started, you’re not part of that exclusive club.

 

[suprarx7nut]

Some of what he says is true, 20 degrees F over ambient rail temp is an accurate number in almost all instances. I've seen 30 -35 on occasion, all normal and doesn't really matter up to a certain unknown temp higher than 160. What matters is the ability of the tank to shed heat. If it doesn't you're F ed.
Your actual liquid temp in the rail goes up dramatically after shutdown. Upon start up it cools back down exponentially faster.
The higher the tank temp the easier it is for that volume of fluid to equalize with the rail or block temp.
We all know this I hope. I hope we also know that there is only one way the fuel tanks get pressurized with a gas(air)
Ignore the pressure volume temp thing and focus on the liquid process.

Personally I find It silly to think that fuel 15 years ago is the same as it is today and should power all vehicles as it did when they were new.
It will get worse year after year.
Controlling the tank temp is the goal. Seems pretty simple to me, and here we got 30 some pages of stuff.

Failure of the purge system to move enough vapor from the tank into the engine through the evap system?

I might be bit of a loner on this, but I believe the purge system should handle any and all vapors, regardless of temperatures anyone has shown here. 140? fine. 160? fine. I'm not aware of any design limit on fuel temperature for that system within the realm of real world scenarios discussed here. Purge system should take all that excess vapor and run it through the engine during the purge cycles the ECU turns on and off as you drive/idle. If the tank builds pressure in ANY climate on planet Earth, the purge system should relieve that pressure via purge. If the tank pressure increase rate overcomes the available purge flow rates then you just need to increase the purge flow rates until it can manage the vapors.

Lowering temps helps because you're reducing vapors, sure, but it's a bandaid, IMO. You should not need to minimize vapors. The purge system is intended to handle all the vapors you could ever produce with any mix of gasoline (yes, even pesky politically-driven-nonsense ethanol). I also think the heat reduction methods will be less effective in the high-temperature areas like Phoenix, Palm Springs, Death Valley, Dubai, etc... where the road surface is 160F-180F. There's not a lot of cool air to help in those situations, but there's still hope if the purge system has enough capacity.

I'll see if the data supports my theory, and then try to disprove my theory and see if I can get anywhere. I suspect there's a big pressure gradient somewhere along the purge system and that will ID the restrictive component(s). Maybe I'll be wrong.

 

[jerryb]

Yes I agree.

I'd still say the root cause is the fuel temp. Without that there would be no excess gas pressure. Would Toyota purposely engineer for
pressurization beyond the ability to purge?

I would think if it was a restriction like a bent or swollen hose, or gummed up valve, someone would have already found it.

If I could get my car up to the boiling in the rail temp I could give an answer as to what it is with X gas, from X station in X state.
I haven't been able to for 3 or 4 years. It's over 167F though, for 87 grade in Florida.

 

[2001LC]

When do our fuel pumps start pumping during start procedures? Not sure if being able to manually enable the fuel bump could preemptively start circulating fuel through the system for a minute or two prior to start?

When engine cranking.
Fuel flow can be tested in the field, without tools. But word of caution: Gasoline is highly flammable. One must have fire extinguisher, and hose to run fuel away from engine and capture it. Disconnect fuel line from fuel filter, then connect hose to fuel filter leading fuel away from hot engine and any spark to a catch can. Crank engine. Fuel should flow out filter through hose while cranking.

The question is WHY are so many of us finding and correcting boiling issues? My 100 in question minus 255s and mild OME lift is near stock, and maintained. This happens to me in heat, or when light towing, or just driving around at altitude.

I've a 00LX w/350K+ miles and a 07LX 165K miles. Both pure stock. Both "were" basket-cases with many issue. I'm still testing the 07LX. But neither now overheat or boil fuel. So it's not every 100 series or every late model. Also I hear reports from around Colorado, that most do not have the fuel boiling issue.

I've corrected many that were overheated and/or boiled fuel. Each case they had issues need correcting. But once back to factory spec they did fine. Except as I've previously mentioned.

Number one thing I'm finding is: coolant system issues. it most every case they'd been to many shops for service and felt they had a very well maintained. They didn't!

The only logical answer is that Toyota did not truly nor fully field test the UZJ100 (especially later models). Design assumptions were made and production run.

Can't say what Toyota did or didn't do as far as field testing in 06-07. I do know the 06-07 have many changes for environmental (EPA) reasons.

I fully, totally respect you and your knowledge base exceeds mine by miles, but I have to disagree: your statement is just too general. There are terribly-maintained vehicles that don't have this problem. Crappy old Jeeps, GMs, Fords run circles around many of us when this occurs. A Jeeper with more accessories and loaded down ridiculousness than I've ever seen kept circling back to us and asking if we needed help and laughing the entire time.

Super-over-built 60s, 80s, and early-model 100s with fuel boiling and squirting out the fuel door don't have this problem. Somewhere, somehow Toyota missed something in these late-model 100s.

Thank you for the respect. I've no problem with you disagreeing. I'd be the first to say, I've a lot to learn about these 100 series and do daily. I change opinion and procedure as I learn. I'm sure I'll learn and adjust on this issue. But I do disagree with "all" have this issues. But I will say, "all can" develop the issue.

I'll not say Toyota didn't make some design flaws. In fact I'm in the testing faze of mod, correcting one on the VVT engine now.

We've a few difference through the years, that may explain some of why later models are harder to correct.
Most notable to subject of fuel boiling.
1) 03- moved charcoal canister to rear. I'm thinking this lends itself to damage, that the pre 03 doesn't.
2) 06-07 have a different fan clutch and fan. Likely to reduce drag to increase fuel economy. This could in part explain the high ECT with higher OAT.

Quite literally brand-new OE pump. December 2020 Toyota battery and I've never had any oxidation. 2yo OE radiator for preemptive maintenance. Admittedly, I've not run AC impedance nor DC resistance on the fuel electrical wires, but I mean we are all supposed to go through wiring resistance tests on Land Cruisers to have a level of confidence with the vehicle?

I removed my fuel line wrapping because I felt it was actually causing subsequent-start issues by trapping (insulating) heat in the lines during shorter stops causing many restart problems for me.



Why Toyota removed the electric pusher fan is beyond me. Oh and BTW all of my scenarios are sans AC running.

I maintain that this is a true design flaw.

I'd like to know if you have/had belly pan or aftermarket skids?

Keep in mind the radiators need constant cleaning. More so after driving on/in/through: Dirt roads, weeds/grasses, deep water, bug swam. Also when R&R radiator, the oil cooler and condenser radiator fins must be cleaned.


I've lost count of how many radiators fins I find clogged, reservoir hose plugged or curled upward, bad rad caps, thermostat bad or wrong (not OEM and or jiggle valve not at top), coolant low. Fact is 98 out of 100 I see have coolant system issues. They didn't come from factory this way.

I've said since the first one I corrected, by getting back to spec. That damage may have accrued to EVAP system. I think damage is likely within charcoal canister and venting of vapor from it. I think damage is greater and has more affect in later years, due to changes through the years. Number one being CC move to rear.

 

[suprarx7nut]

Yes I agree.

I'd still say the root cause is the fuel temp. Without that there would be no excess gas pressure. Would Toyota purposely engineer for
pressurization beyond the ability to purge?

I would think if it was a restriction like a bent or swollen hose, or gummed up valve, someone would have already found it.

If I could get my car up to the boiling in the rail temp I could give an answer as to what it is with X gas, from X station in X state.
I haven't been able to for 3 or 4 years. It's over 167F though, for 87 grade in Florida.

No, but I think they may have designed it with less over-capacity than we see with most other parts of the vehicle. I could see them designing the purge to handle the vaporization they saw with low/no ethanol fuel at the time of design, with a maintained cooling system, with no exhaust leaks, without extra skid plates and with fresh cats. Over time I think all those factors could team up and overwhelm the purge system which was initially designed correctly.

I guess in my mind, you can try to offset a bit (maybe most) of the problem with temp (assuming you live in a climate where it's cool enough to actually work) or you could just up the capacity of the purge system until none of those factors (even when combined) are enough to overwhelm it. You can't cool the fuel system enough to give yourself anywhere near the headroom that you can create with a little more purge capacity. You could triple the purge capacity with ease, I believe. You can't get that same result with any level of cooling unless you tie in some refrigerant-based heat exchanger method or something.

Of course, I don't think my thought here helps to do anything for the no-start or poor running problems that might also go along with hot fuel. I'm just trying to avoid drooling fuel out my filler neck, ruining my paint and potentially burning my car/occupants.

 

[tucker74]

I disagree here, I’ve had my ‘06 since 22k miles and it’s been meticulously maintained and never had any cooling issues. The first time I experienced was in CO at hundreds in the hills ‘16, it was warm and we were over 14k. The truck had 44k at the time and no external mods, 7-8 trucks experienced the same on that trip.

tucker

*was replying to 2001LC where he stated trucks probably had cooling issues that were experiencing