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

[2001LC]

Just added this to OP:

Anyone having and OBDII reader that can watch engine coolant temp and report back here, would be very valuable data. Whether having these issue or not. Other data points in order I feel of most value along with engine coolant temp; Long term Fuel trims (LT FT), Engine RPM, MPH, CAT Temps.

 

[d4nvu]

Interesting but I dont think that flap matters. I have an 03 that I had the tank and filler neck replaced OEM at dealer and bother before and after I had no flap. My be a year think or an LC vs LX??

As seen in some of the previous posts the gas cap seems to be the secondary release point for pressure in event evap system cannot handle excess pressure in tank. Figure out cause/symptoms of the pressure build up or what is failing in your evap system that seems to be the issue.

Likely the flapper fell into filler tube neck or springs came off and it just hanging there hidden from sight. IDK, but tend to agree with @Jfoofighter16 that it likely is not your issue. But let's not rule it out totally just yet. I say this because it could plug air from escaping normally as cap removed. This may give impression of over pressurized.

If you or your buddy has and OBDII that can read temps and fuel trims, hook it up on todays drive. See what reads you can log and report back here.

Ah, I see. I felt around in the filler neck with my finger and did not find any indication of springs/mounting areas of the flap. Mine is an '02 LX and his an '00 LX. Maybe they changed between the years. I hooked up a Scangauge coming back from Tahoe to San Francisco (6000' to 52') to closely monitor Water temp (I forgot to measure fuel trim.) and ranged from 186F to 197F as the highest- granted I had a full load (bumpers, winch, RTT, jerry cans, drawers, 33s, and 4 passengers total) and it was 102F outside in some parts of the drive.

Every hour or so on the way back I would pull over and check the gas door to see if there was any seepage and the new gas cap seemed to be holding fine. Really hard to judge, as coming back was more downhill and only some uphill. I want to say, in my case, it seems to be a combination of the newly added weight (drawers/bumpers/winch/jerry cans were added quite recently), temp, and altitude which resulted in my excessive fuel pressure and the gas cap failing. Remember, I just changed the fuel filter so I don't know if that had anything to do with it. I kept my older one just in case I need to swap it out to see any change. I did not mention this earlier, but I was AND still experiencing a little bit of lose in power as well when my foot is on the gas pedal on highway speeds. The truck bogs 2-3 times for a split second. The RPMs do not drop a lot, but the loss in power is noticeable. This was happening to and from Tahoe. Feels like fuel is cutting? Maybe a misfire? I have not seen any CELs. Funny that a thread describing what is happening would also come up today. LINK

I will still keep a close monitor and will report back if I see anything else.

 

[2001LC]

Ah, I see. I felt around in the filler neck with my finger and did not find any indication of springs/mounting areas of the flap. Mine is an '02 LX and his an '00 LX. Maybe they changed between the years. I hooked up a Scangauge coming back from Tahoe to San Francisco (6000' to 52') to closely monitor Water temp (I forgot to measure fuel trim.) and ranged from 186F to 197F as the highest- granted I had a full load (bumpers, winch, RTT, jerry cans, drawers, 33s, and 4 passengers total) and it was 102F outside in some parts of the drive.

Every hour or so on the way back I would pull over and check the gas door to see if there was any seepage and the new gas cap seemed to be holding fine. Really hard to judge, as coming back was more downhill and only some uphill. I want to say, in my case, it seems to be a combination of the newly added weight (drawers/bumpers/winch/jerry cans were added quite recently), temp, and altitude which resulted in my excessive fuel pressure and the gas cap failing. Remember, I just changed the fuel filter so I don't know if that had anything to do with it. I kept my older one just in case I need to swap it out to see any change. I did not mention this earlier, but I was AND still experiencing a little bit of lose in power as well when my foot is on the gas pedal on highway speeds. The truck bogs 2-3 times for a split second. The RPMs do not drop a lot, but the loss in power is noticeable. This was happening to and from Tahoe. Feels like fuel is cutting? Maybe a misfire? I have not seen any CELs. Funny that a thread describing what is happening would also come up today. LINK

I will still keep a close monitor and will report back if I see anything else.

I happen to have 00LX, 02LX, 07LX & 06LC here today. Only the 00LX has the fill neck flap.

Temp 186F to 197F is on high side:
Heavy laden, AC frt & rear and OAT of 102F it would seems 197F isn't out of line. But it is a little high. I'd check radiator fins first for grass, cotten, bugs, ect. clogging. Also if coolant has not been flushed in last two years, I'd flush it with Toy SS (red)! If no record of thermostat & radiator cap being replaced in last 90K, I'd replace them also.

Hastation & temp:
I'd do a major tune. Which includes replace all vacuum line cracked, including PCV grommet. Also spark plugs and coil boot kit, better yet coils.

 

[J1000]

I was laying in bed last night thinking about the return fuel routing and how it would be a pain in the neck to shield the lines on the rear of the engine behind the intake manifold. Then it hit me, why don't I just use a new section of fuel hose and reroute it up and away from the engine? Not only that but the stock return tubes are metal and bolted on to the aluminum heads. That is just going to ensure excellent heat transfer from the block to the fuel. At the same time I used some of the handy tube heatshield over the top of the lines. I think I'm going to reorder in slightly larger size and in black.

Not enough miles to tell but I will be monitoring fuel temps going forward.

Gates 5/16 fuel line: Amazon.com: Gates 27340 Barricade MPI Fuel Line Hose: Automotive
Heat shield tubing: https://www.amazon.com/gp/product/B000CEO5T6/?tag=ihco-20
Fuel Temp/Ethanol Content Sensor and Gauge: Amazon.com: Innovate Motorsports 3904 MTX-D Dual Gauge Kit -Ethanol/Fuel Temp, 1 Pack: Automotive

Stock return lines below and then my new line:

 

[abuck99]

I've been keeping track of temps all over the fuel circuit for the past few weeks with IR gun. Granted IR gun won't tell me how hot it is inside the pipe/hose but it does indicate to me heat soak hotspots along the way. It would seem that there's some heat soak to the return line cross the back side of the engine- I dont think its enough to warrant moving the line-possibly wrapping it with silicone tape or reflective wrap like you have there might make a small difference. But in my checking so far, the temps on that line and fittings haven't been substantially different form other sections of the fuel circuit as it makes its way from one side of the engine to the other. Ive been checking temps at inlet fitting at fuel filter, base of pulsation damper, banjo bolt at front DS crossover, banjo bolt and PS cross over terminus, FPR inlet, FPR outlet, PS where rear crossover turns to steel pipe, DS where it turns back to rubber and last where rubber meets the steel return line on the fenderwell. I haven't seen more than a few degrees difference between inlet and return through out the entire circuit. All temps being in the 135 F range (+/- 4). This is testing in +90F (intake temps 110F +/-) ambient temps city driving for 1hr.

I revert to my belief that the health of the fuel pump & FPR have more impact on heat soak than fuel lines across the engine. Not saying the proximity to the cat doesn't have a contributing effect, or where the Y-pipe joint meets the muffler pipe ( an area prone to exhaust leak and heating the front side of the tank). Just have to make sure the pump is strong and moving the fuel as it heats up. Old pumps get weak, more affected by heat and pump pressure and delivery drops-fuel heats up more.

 

[d4nvu]

I happen to have 00LX, 02LX, 07LX & 06LC here today. Only the 00LX has the fill neck flap.

Temp 186F to 197F is on high side:
Heavy laden, AC frt & rear and OAT of 102F it would seems 197F isn't out of line. But it is a little high. I'd check radiator fins first for grass, cotten, bugs, ect. clogging. Also if coolant has not been flushed in last two years, I'd flush it with Toy SS (red)! If no record of thermostat & radiator cap being replaced in last 90K, I'd replace them also.

Hastation & temp:
I'd do a major tune. Which includes replace all vacuum line cracked, including PCV grommet. Also spark plugs and coil boot kit, better yet coils.

Thanks, just received my Spectra radiator today so that will be going in soon (mine has been brown for a little while now). Will be replacing my radiator, upper and lower hoses, thermostat, cap, and of course flushing and topping off with Toyota Red.

Where can I find a part list of vacuum lines to replace?

 

[2001LC]

Thanks, just received my Spectra radiator today so that will be going in soon (mine has been brown for a little while now). Will be replacing my radiator, upper and lower hoses, thermostat, cap, and of course flushing and topping off with Toyota Red.

Where can I find a part list of vacuum lines to replace?

Vac lines vary by year. So look over which need replacing (cracked or loose). Input your VIN # at www.partsouq.com

 

[caslim]

186F to 197F is actually normal operating. Hotter climates range more around 195-205.

 

[Whoareu2200]

just happened to me but i did top off gas before hitting trail. First time happened to me

 

[2001LC]

just happened to me but i did top off gas before hitting trail. First time happened to me View attachment 2370116

WOW dangerous.

Some detail would be nice, like:
Year?
Miles?
Has radiator fins been cleaned or radiator replaced?
How old (miles and years) is thermostat?
How old (miles and years) is Radiator cap?
Vacuum lines in good condition?
Last tune up and what done.
Last coolant flush?
Coolant level
Engine coolant temp, during the trip on this day?
What all aftermarket mod, weight on this rig?
Belly pan or factory undershielding/skids.
OAT at the time?
Altitude at start of tail and at this point it boiled over?
How steep incline and descents?

Why do you think this happened?

 

[2001LC]

186F to 197F is actually normal operating. Hotter climates range more around 195-205.

In post #2, you'll see I was reading 184 to 189 only touching 190F for a moment. OAT of 75 to 95F both AC on full for a 6 hour drive, in 99LC. That was city, mountain and the stop and go HWY (grid lock) with 3PM sun OAT 95F.

Now graded, it was factory temp sending unit and I had just serviced cooling system including flush with BG flush and add a can of BG Supper cool. I've no idea if Super cool helped.

Note: Thermostats OEM which is 82C (179.6 F)

 

[Whoareu2200]

1k miles old

New radiator
New radiator cap
New timing belt w water pump and thermostat
200k miles on vehicle
2003

Temp never past half way like normal.

arb bumpers front and back.
Roof rack

Will check vacuum lines.

She never felt different. Just happen to pull over for someone else when i noticed the smell and hurd the bubbles

I dont know why it happened. I did top it off right before hitting the trail. This is my second time on this trail. First time went w wifey and it didnt do it. But didnt go too high like this time

 

[guardcompany]

I too had this happened to me right after a new OEM Toyota radiator and thermostat. I don't think it's just a cooling system issue.

I just did the O2 sensors, built the heat shield, wrapped the fuel lines, replaced the fan clutch and replaced the fuel pump and I'm off to Colorado in 2 weeks. If it still happens the only thing it could be is the EVAP/vac lines/CC. I've done everything else.

 

[Whoareu2200]

Did feel alot of heat coming from driver side catalytic. When airing back up No check engine light.

 

[Whoareu2200]

I will replace fan clutch since I havent and wont hurt to have a new one at 200k

Let us know how it goes hopefully its fixed for you

Ill prob just replace vac lines since it wont hurt either

 

[Jfoofighter16]

So I've been posting on this thread and another one with all the thing over replaced over the past year/winter (list is long and not re typing here but look at old posts and you'll see how much I've replaced) just to have this problem still occur this year on hot days almost wherever I drive in C. Springs area even if not running trails at altitude. I will say that after everything I replaced it seem to help but not eliminate the problem.

So I went for the long shot here that some posts swear by and a few weeks back started running ethanol free during a road trip to north dakota (with my camping trailer, pictured) and had zero venting. When changing fuel I noticed the pressure wasnt as much when I opened the cap either. Octane was 91 on trip, but now that back in CO mainly finding 87.

I know you are going to say ND is lower in altitude but I've done 10-12k on hot afternoons past two weekends on trails here in CO and never even smelled a whiff of gas and usually I'd be gurgling/venting. I will say I have EVEN LESS pressure with the 87 versus 91 octane ethanol free as well. So I am officially now a user of Maverik and Murphy Express app (as they seem to be the only options consistently with ethanol free in CO). Also using pure-gas.org a lot too to find stations along trips.

Unfortunately this also means I now find myself planning trips around whether I have ethanol free fuel nearby but so far I'm finding it and also not venting which was my only goal at the start of this mystery hunt.

Will update if anything changes here but i recommend folks with this issue start running ethanol free and see if it starts making a difference. I also think the O2 sensors made a big difference, replaced all 4 this last winter and cats seem to overheat less.

 

[2001LC]

I really like to know; what each and every engine coolant temp is running?
I've seen 205F on engine temp, through a scan gauge (in my case BlueDrive via iphone app), while dash gauge hovering around center line. The dash gauge just will not be of use for collecting data. If you see dash temp gauge reading hot pull over, your burning up the engine. Also be alerted to low temp indication of dash gauge, indicting running cool. This can be worst case overheating, due to low coolant. This one warps heads and blow engines. Gauge should always be near center line, after warm up.

I stress again. Let get some hard data on the actually temps?

I'd also like to see fuel trims and RPMs along side temps?
This give idea of engines running condition while temps going up or down. My BlueDriver allow me to monitor and than save/send the data. I go then go back and review actual temps. If one has a vacuum leak, engine will run lean, which raises cylinder head temp. Also vacuum leak may reduce suction of vapors from fuel tank.

Weight and vehicle build may also yield clues. More info the better?

Year matters?
If one has and 03 up and has had this issue of fuel boiling. It's almost a sure thing the charcoal canister is toast. So once we know coolant and vacuum under the hood in order. My next step if one comes to me is work through the EVAP system. We have 2 possibly 3 different designs or variation in the EVAP of the 100 series. So what works to correct in one rig may not work as well in other. If we're going to solve this issue in the near term. The collective data of the forum will be invaluable. The devil is in the detail as they say.

Does your gas cap fill area need cleaning?
What I've noticed with gas cap fill area. That is, the gunk buildup under the body gas cap fill door. This indicates fuel boiling and vapor or raw fuel being expe Indicates EVAP system would be gunked.

I'm also wonder how much the factory #1, #2 and gas tank shielding matter. What do you have?
The #2 undercarriage shielding, has tails. Why did factory put those tails there. Most are busted from vehicle being lifted on a rack at tires shop. Do these protect CATs from road heat or help direct air follow. I once had a VW bug, darn thing keep running hot. Even just shutting down, while descending from Flagstaff to Phoenix. Turns out a very small heat heat shield was missing, at back of engine. This shield directed air follow and keep roads radiated heat and air defected from engine.

Some may have notice in post #2. I replace vacuum lines. One was to CC, which was old and cracked. That one may have improved suction from CC to engine. I also replace fuel pressure regulator (FPR). That was a though I had, that weak FPR may be allowing to much fuel back to tank to fast. It also could reduce fuel pressure at the fuel injectors (fuel rail pressure). This also creates a lean condition.

 

[Jfoofighter16]

I really like to know; what each and every engine coolant temp is running?
I've seen 205F on engine temp, through a scan gauge (in my case BlueDrive via iphone app), while dash gauge hovering around center line. The dash gauge just will not be of use for collecting data. If you see dash temp gauge reading hot pull over, your burning up the engine. Also be alerted to low temp indication of dash gauge, indicting running cool. This can be worst case overheating, due to low coolant. This one warps heads and blow engines. Gauge should always be near center line, after warm up.

I stress again. Let get some hard data on the actually temps?

I'd also like to see fuel trims and RPMs along side temps?
This give idea of engines running condition while temps going up or down. My BlueDriver allow me to monitor and than save/send the data. I go then go back and review actual temps. If one has a vacuum leak, engine will run lean, which raises cylinder head temp. Also vacuum leak may reduce suction of vapors from fuel tank.

Weight and vehicle build may also yield clues. More info the better?

Year matters?
If one has and 03 up and has had this issue of fuel boiling. It's almost a sure thing the charcoal canister is toast. So once we know coolant and vacuum under the hood in order. My next step if one comes to me is work through the EVAP system. We have 2 possibly 3 different designs or variation in the EVAP of the 100 series. So what works to correct in one rig may not work as well in other. If we're going to solve this issue in the near term. The collective data of the forum will be invaluable. The devil is in the detail as they say.

Does your gas cap fill area need cleaning?
What I've noticed with gas cap fill area. That is, the gunk buildup under the body gas cap fill door. This indicates fuel boiling and vapor or raw fuel being expe Indicates EVAP system would be gunked.

I'm also wonder how much the factory #1, #2 and gas tank shielding matter. What do you have?
The #2 undercarriage shielding, has tails. Why did factory put those tails there. Most are busted from vehicle being lifted on a rack at tires shop. Do these protect CATs from road heat or help direct air follow. I once had a VW bug, darn thing keep running hot. Even just shutting down, while descending from Flagstaff to Phoenix. Turns out a very small heat heat shield was missing, at back of engine. This shield directed air follow and keep roads radiated heat and air defected from engine.

Some may have notice in post #2. I replace vacuum lines. One was to CC, which was old and cracked. That one may have improved suction from CC to engine. I also replace fuel pressure regulator (FPR). That was a though I had, that weak FPR may be allowing to much fuel back to tank to fast. It also could reduce fuel pressure at the fuel injectors (fuel rail pressure). This also creates a lean condition.

I have seen coolant temps from 189 to 205 and cant seem to drive a correlation to the boiling/venting. Also I cant make heads/tails of fuel trim data but I can save some and see I'd I have any saved from previous trips where I did vent on by bluedriver app.

I think, knowing everything inknow from the repairs I've done, MUD posts and my experience now with ethanol free fuel my theory is that there are a combination of failure points that could cause heating and/or evap system to be overstretched...as a post on this thread with a youtube video link to evap system overview showed, there is a stop valve within tank to prevent gas from getting into evap system. When this happens the pressure has no choice but to release at the secondary point which is the gas cap that has a spring built in to release this pressure when too much. By fixing exhaust system/cat issues and O2 sensors I think SOME of the heat can be controlled but our older rigs seem to build up heat regardless.

As for the ethanol free fuel, I'm not a scientist and dont know how/why but I seem to no longer build up so much pressure that the stop valve in tank to the CC isnt tripping (even with full tank on hot day) and therefore CC is working and no pressure out of gas cap. I say this bc I did run in traffic on a hot day last week where last year i would have been boiling or when i turned car off i would have at least heard/smelled fumes from gas cap. When I turned car off I had no gas cap venting/smell and could hear pressure going to CC to then burn off that stuff at next startup as intended.

Sooo this leads me to think MAYBE the stop valve in tank wears out over time to where it either gunks up or takes hardly any pressure to close up and not allow pressure to CC. Perhaps if I replace this I could test theory and run some ethanol fuel and see if tank can handle the increased pressure i experience with this fuel type.

In the meantime, I'm running ethanol free 87 octane and not having to stress in the back of my mind all day every day during the summer whether I'm going to vent from my tank!! That's my $0.02 as of today but I am always learning here!

 

[2001LC]

I have seen coolant temps from 189 to 205 and cant seem to drive a correlation to the boiling/venting. Also I cant make heads/tails of fuel trim data but I can save some and see I'd I have any saved from previous trips where I did vent on by bluedriver app.

I think, knowing everything inknow from the repairs I've done, MUD posts and my experience now with ethanol free fuel my theory is that there are a combination of failure points that could cause heating and/or evap system to be overstretched...as a post on this thread with a youtube video link to evap system overview showed, there is a stop valve within tank to prevent gas from getting into evap system. When this happens the pressure has no choice but to release at the secondary point which is the gas cap that has a spring built in to release this pressure when too much. By fixing exhaust system/cat issues and O2 sensors I think SOME of the heat can be controlled but our older rigs seem to build up heat regardless.

As for the ethanol free fuel, I'm not a scientist and dont know how/why but I seem to no longer build up so much pressure that the stop valve in tank to the CC isnt tripping (even with full tank on hot day) and therefore CC is working and no pressure out of gas cap. I say this bc I did run in traffic on a hot day last week where last year i would have been boiling or when i turned car off i would have at least heard/smelled fumes from gas cap. When I turned car off I had no gas cap venting/smell and could hear pressure going to CC to then burn off that stuff at next startup as intended.

Sooo this leads me to think MAYBE the stop valve in tank wears out over time to where it either gunks up or takes hardly any pressure to close up and not allow pressure to CC. Perhaps if I replace this I could test theory and run some ethanol fuel and see if tank can handle the increased pressure i experience with this fuel type.

In the meantime, I'm running ethanol free 87 octane and not having to stress in the back of my mind all day every day during the summer whether I'm going to vent from my tank!! That's my $0.02 as of today but I am always learning here!

I assure your 189 to 205f indicates something not to factory specs. 205F should only be seen in the most demanding, hot OAT and loaded condition. Even then something is not right. 205F and your CAT will be very hot. I'll take a look at your rig, anytime you'd like to stop by. Please wear a mask (covid BS) here, I will also.

We're thinking along the same lines. That damage is cause by the condition over time. That the fuel shut off valve on vapor return line, may be getting stuck. But looking at parts diagrams in PQ. I do not see this shutoff valve after 02-. Those have CC in back and we may need to approach differently. But first all things under hood need to be at spec regardless of year..


I was just driving my 00LX w/350K+ miles (Emerald) in stop and go gridlock.:
I've never notice fuel smell, before. But on this day I did, at end of 3 hours stop and go driving around and in Denver at 99F OAT. Traffic is worst than ever these days, with people avoid public transportation. So this was worst case driving. I open the gas cap and got ~3 seconds of hiss, then put cap back on. I then heard CC humming. Went back and released cap again, and got 1 second of hiss. So gas must have been boiling somewhat. The system did it's job. This coolant system is spot on, except old fan clutch, which seems okay (aged). BTW; It's my understanding, CC vents to atmosphere when engine off. That fuel vapor is sucked into intake when running.

I did not get temps and FT while driving that day. Bluedriver had given me a bata driver to test, and it failed. Darn!

I do have two things on Emerald, I've been wanting to do. That is have fuel injectors serviced by Chuck (FIS) and replace the old factory fuel pressure regulator.

Note: I have extensive service history on Emerald. I don't have first 100K mile out of canada Dealerships, but most all for last 250K miles. It is the longer/thickest service history I've seen. Never any mention of fuel issue of this topic, that can I recall. I take another look. But it spent time in many parts of North America, and last few year in Ft Collins foothills at about 6,500 feet. It was a good climb on slow road too, where it lived. All back top and no shade. So it had, hot, long slow drive daily in the summer.

 

[Pskhaat]

So I went for the long shot here that some posts swear by and a few weeks back started running ethanol free during a road trip to north dakota (with my camping trailer, pictured) and had zero venting. When changing fuel I noticed the pressure wasnt as much when I opened the cap either. Octane was 91 on trip, but now that back in CO mainly finding 87.

I know you are going to say ND is lower in altitude but I've done 10-12k on hot afternoons past two weekends on trails here in CO and never even smelled a whiff of gas and usually I'd be gurgling/venting. I will say I have EVEN LESS pressure with the 87 versus 91 octane ethanol free as well.

Yup. This. E0 does not mean pure gasoline though, there is something very very likely added in order to bump up the octane rating. Ethanol does a good job at that, but MTBE and other chemicals would be added. Still, non-ethanol fuel has always done me well: E0 v. E10 gasoline figures over 900 miles.

I would like your anecdote on running 85 low-test, I think you'll find even more success at altitude.