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

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suprarx7nut said:
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.
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I'm trying to understand the mechanism that causes fuel to come out of the filler neck. Is there pressure in the fuel tank that is pushing fuel up the pipe, or is the fuel actively boiling which causes it to bubble up the pipe? If it's trapped pressure from the evap system not keeping up, then I could see increased evep capacity helping. If it's the fuel actively boiling, then higher tank pressure should raise the boiling point and actually help the issue, right? I'm not trying to argue that either of those scenarios is true, rather I'm trying to understand the consensus of the smart people.
 
Eyedaho said:
I'm trying to understand the mechanism that causes fuel to come out of the filler neck. Is there pressure in the fuel tank that is pushing fuel up the pipe, or is the fuel actively boiling which causes it to bubble up the pipe? If it's trapped pressure from the evap system not keeping up, then I could see increased evep capacity helping. If it's the fuel actively boiling, then higher tank pressure should raise the boiling point and actually help the issue, right? I'm not trying to argue that either of those scenarios is true, rather I'm trying to understand the consensus of the smart people.
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The fuel cap is the "final" safety pressure relief. Once the tank builds enough pressure to be a safety risk, the cap vents to avoid the tank bursting.

Higher pressure would raise boiling point, but the tank cannot withstand any meaningful pressure over atmosphere. Gasoline isn't a single component with a flash boiling point, either. Different compounds of the gas will evaporate/boil at varying temps/pressures/rates. Boiling point is generally somewhere between 180-400F I think.

As far as liquid fuel coming out of the cap, consider how sprinklers blow out. Water spits out even when 90-99% of the flow is compressed air. Some liquid will follow along with the vapor flow. That's how I picture it, at least. There may be more phase change physics involved, too.
 
You need to add additional absorbed energy to a system at boiling temp to cause vaporization. It's called latent heat of vaporization. It's usually not a small number. This is exactly why it takes a long time to completely vaporize your pot of water once it starts boiling. Some physics while on the throne

The fuel system acts like a coolant system when the fuel evap system can't keep up. When you hit red on the temp gauge and pop that radiator cap, the pressure relief is both gas and liquid that goes along for the ride.
 
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I agree with you supranut. it doesn't vent well enough. But that's the band aid imo

If it did vent enough then lowering the pressure in the tank only makes it worse, cascading to liquid fuel coming out the gas cap.
It's so violent that the liquid comes out with the gas trying to escape. Assuming temp isn't a problem that should be remedied and toyota should have made it so fuel temp doesn't matter.

People click the cap open a tiny bit and we know what happens.
The decompression event in the tank that occurs when you open the cap a few clicks lowers the boil point drastically by way of lowering the pressure. Then it boils off more raising the pressure, because temp is still too high. (nevermind the decompression cooling effect) More gas and liquid come out the filler neck as it tries to continually equalize. It is self sustaining. It will continue until the pressure is high enough that it won't boil, the temperature is low enough that it won't boil, or there is no liquid left to boil.
The cap is just the easiest place for it to escape to. Or just the weakest link.

All those things are related.
pressure, volume and temp in liquid and gas states. They all have to be controlled.
Your ethanol laced gas (and others) boils after the regulator where it's theoretically at one atmosphere absolute. The reality is slightly above.
Before the regulator it's normally at 40psi gauge or 54 psi absolute, at least until shutdown where the only pressurized liquid is between the top of the fuel pump and the pressure regulator. Which at the same time is bleeding down because the fuel regulator is not a true check valve and the one at the top of the pump is just slightly able to hold pressure. Theoretically that slug of liquid should always be safe. From boiling.

So then it gets pushed downline if the car is running and cooled down by the volume of gas and liquid in the tank at a theoretical zero by gauge and if the car is turned off it just boils and expands downline to the tank. Where normal venting may occur.
Which leads back to the overpressure occurring in the tank. Overcoming the engineered vents. At a temp well below 200F


You have to control those 3 things, temp, volume, or pressure. Volume is type and quantity of fuel.
Toyotas answer to pressure control is inadequate for todays fuel in certain regions in the USA.
That leaves temp.

Hopefully everyone realizes that fuel is different in other regions in the USA and without a doubt is different in each country.
That's why you don't hear about this in other less climate concerned countries.

That's how I see it. Simple. I'd add a cooler after checking voltage, pressure, and leakdown #s
 
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tucker74 said:
I disagree here, I’ve had my ‘06 since 22k miles
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How many miles now?
Ever fill the gas tank and squeeze pump handle one more time, after auto shut off. Or could someone have the first 22K miles?
tucker74 said:
and it’s been meticulously maintained and never had any cooling issues.
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So assume over 100K now. You've washed the radiator fins at least 20 times or more if driven off-road or in very dusty, cotton or bug, etc. condition?
You've replace thermostat and rad cap with OEM at least once by now?
Assume you're over 100K, so have replace spark plugs?
That TX heat is so hard on rubber. So you've replace all the vacuums lines (EVAP, PCV & Idle up) or at least made sure no leaks?

tucker74 said:
The first time I experienced was in CO at hundreds in the hills ‘16, it was warm and we were over 14k.
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What was the ECT & AT temp?
tucker74 said:
The truck had 44k at the time and no external mods,
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44K. The fuel tank treatment?

tucker74 said:
7-8 trucks experienced the same on that trip.
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Out of how many, 100 or more rigs.
tucker74 said:
tucker

*was replying to 2001LC where he stated trucks probably had cooling issues that were experiencing
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Of all I've worked on, but one. Correcting coolant issue, fix the fuel boiling issue.

I'm not saying every 100 has coolant issue. But I am saying most that come to me for service do!

Number one issue is clogged radiator (all 3) fins.
 
There could also be some real argument that the switch in pumps for vvti was a result of trying to mitigate the temp issue.
Smaller pump, if there is a real tangible difference, should be less heat but with a trade off in volume pumped.
The resistor might have been added to combat heat at the pump as well. It has no real effect on volume or pressure change to the injectors but lower flow rate overall.

Someone should bridge the resistor connector and see what happens, see if any check engine lights come on. I bet they wouldn't.
 
jerryb said:
I agree with you supranut. it doesn't vent well enough. But that's the band aid imo

If it did vent enough then lowering the pressure in the tank only makes it worse, cascading to liquid fuel coming out the gas cap.
It's so violent that the liquid comes out with the gas trying to escape. Assuming temp isn't a problem that should be remedied and toyota should have made it so fuel temp doesn't matter.

People click the cap open a tiny bit and we know what happens.
The decompression event in the tank that occurs when you open the cap a few clicks lowers the boil point drastically by way of lowering the pressure. Then it boils off more raising the pressure, because temp is still too high. (nevermind the decompression cooling effect) more gas and liquid come out the filler neck as it tries to continually equalize. It is self sustaining. It will continue until the pressure is high enough that it won't boil, the temperature is low enough that it won't boil, or there is no liquid left to boil.
The cap is just the easiest place for it to escape to. Or just the weakest link.

All those things are related.
pressure, volume and temp in liquid and gas states. They all have to be controlled.
Your ethanol laced gas (and others) boils after the regulator where it's theoretically at one atmosphere absolute. The reality is slightly above.
Before the regulator it's normally at 40psi gauge or 54 psi absolute, at least until shutdown where the only pressurized liquid is between the top of the fuel pump and the pressure regulator. Which at the same time is bleeding down because the fuel regulator is not a true check valve and the one at the top of the pump is just slightly able to hold pressure. Theoretically that slug of liquid should always be safe. From boiling.

So then it gets pushed downline if the car is running and cooled down by the volume of gas and liquid in the tank at a theoretical zero by gauge and if the car is turned off it just boils and expands downline to the tank. Where normal venting may occur.
Which leads back to the overpressure occurring in the tank. Overcoming the engineered vents. At a temp well below 200F


You have to control those 3 things, temp, volume, or pressure. Volume is type and quantity of fuel.
Toyotas answer to pressure control is inadequate for todays fuel in certain regions in the USA.
That leaves temp.

Hopefully everyone realizes that fuel is different in other regions in the USA and without a doubt is different in each country.
That's why you don't hear about this in other less climate concerned countries.

That's how I see it. Simple. I'd add a cooler after checking voltage, pressure, and leakdown #s
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Wait a minute. I think there's a fundamental question we need to agree on or discuss.

My assumption/preposition: Boiling point of gasoline is nowhere near any of the temps we've recorded in the 100 series fuel return lines or the tank itself. Boiling point of gasoline is variable, but likely 200F+ (probably closer to 300-400F). Agreed? I see some sources stating boiling point of modern blends is around 300-400F. Way outside of anything anyone here has measured. Boiling isn't the problem, is it? It's vaporization... right? Vaporization happens at a wide range of temps, unlike boiling which you could stop if you keep temp low enough.

The pressure in the tank that activates the gas cap pressure relief is very low. Something like .5 psi. Not enough to significantly change the boiling point or vaporization. The tank really can't take any pressurization.

I think you're coming at this with some assumptions of a pressure cooker or something. It's often assumed and desired to have *vacuum* inside the tank (because the purge system is constantly sucking on the tank when all things are going as planned). Venting excess pressure to maintain near atmosphere in the tank won't change the boiling point (and we're nowhere near it to begin with). You can collapse the gas tank by vacuum force before you have any kind of liquid boiling problem. Even then, the boiled vapors just go into the engine, so no harm, no foul.


Am I alone in this belief?
 
Boiling point of gasoline is nowhere near any of the temps we've recorded in the 100 series fuel return lines or the tank itself.
cant be true
Boiling point of gasoline is variable, but likely 200F+ (probably closer to 300-400F). Agreed?
no
I see some sources stating boiling point of modern blends is around 300-400F.
no
Way outside of anything anyone here has measured. Boiling isn't the problem, is it?
yes
It's vaporization... right?
yes
Vaporization happens at a wide range of temps, boiling which you could stop if you keep temp low enough.
I guess yes and no. Ones quicker and more violent. You could stop both with temp and enough money.


There is so much online to read. someone reading this probably has graphs with temp, vapor pressure and what boils off first.

I think it's generally agreed that it's 100-400 for gas and 173 for ethanol, all Fahrenheit. remember that the return line has no meaningful pressure behind it.

two examples I just looked at.

Absolutely, the people with issues are above 180-200F at the rails. Absolutely some components are evaporating faster than they should.
boiling is a faster process of evaporation. Which does occur if you rapidly decompress from the pressure side to the non pressure side of the fuel regulator. You should expect boil to occur. I would at least.
 
@2001LC I’ve flushed the system at 60k and now again at 100k, full clear flush at peacock & block…never anything but Toyota red. Just turned 100k, did the timing belt, water pump, cam seals and spark plugs with that service. Have not replaced thermostat or radiator cap, or any of the vacuum tubing. Interesting on the clogged radiator, haven’t ever seen cooling issues or elevated temps so have not checked specifically. Guessing there isn’t a fix other than replacing? I have seen this issue twice in the last year, once in Big Bend we stopped at a overlook after driving most of the day in hot & dusty conditions with 1/2 tank of fuel. Second ~1hr into a trip pullling a 23’ airstream, kiddo had to use restroom so I decided to top off tank. First one was 20min waiting with fuel cap off, second it flash sprayed when the pump gas hit the tank. 20min sitting before it would start. I recently wrapped all the fuel & vapor lines around DS cat with heat wrap, had read another thread where this helped. Let me know if there is something else I should try, seems looking into cooling may be prudent if this doesn’t address. Have not chased fuel pump, as I said also saw with much less miles and newer components so skeptical there (cooling/fuel pump/evap).

Yes - 7-8 trucks out of 80 or so, pretty sure all were later vvti

Tucker
 
jerryb said:
Boiling point of gasoline is nowhere near any of the temps we've recorded in the 100 series fuel return lines or the tank itself.
cant be true
Boiling point of gasoline is variable, but likely 200F+ (probably closer to 300-400F). Agreed?
no
I see some sources stating boiling point of modern blends is around 300-400F.
no
Way outside of anything anyone here has measured. Boiling isn't the problem, is it?
yes
It's vaporization... right?
yes
Vaporization happens at a wide range of temps, boiling which you could stop if you keep temp low enough.
I guess yes and no. Ones quicker and more violent. You could stop both with temp and enough money.


There is so much online to read. someone reading this probably has graphs with temp, vapor pressure and what boils off first.

I think it's generally agreed that it's 100-400 for gas and 173 for ethanol, all Fahrenheit. remember that the return line has no meaningful pressure behind it.

two examples I just looked at.

Absolutely, the people with issues are above 180-200F at the rails. Absolutely some components are evaporating faster than they should.
boiling is a faster process of evaporation. Which does occur if you rapidly decompress from the pressure side to the non pressure side of the fuel regulator. You should expect boil to occur. I would at least.
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I can't find time to sit down today so just a quick response from me here, but those links are awesome. Good find and thanks for linking here.

It looks like they have E10 at around 155F boiling and pure gasoline tracking for ~185F. I say this realizing there's a range assumed there, but I'll talk single numbers for ease of conversation. Lower than I expected, but I think still higher than anyone has measured their tank. We've seen fuel return lines at 160F, I think. Tank should be cooler (I suspect a lot), but I guess we don't know by how much.

I agree if you're over the boil point/range in the tank then there's no stopping the problem. I assume though, that not everyone with this problem is into the boil range in the tank. Might be a bad assumption, but I just can't see the tank staying that hot in all these cases. I think instead, we're just seeing a very slow and gradual build up of pressure over what the purge system can vent.

I got my pressure sensors and gauge today. Might have to add a couple temp probes to my data log as well.

Thanks for the response and links. Good stuff.

Quick addition so you know I'm not ignoring it: I think fuel rail temps are relatively meaningless for the tank vent problem. The temps and pressures of fuel going back into tank are different enough that I don't think the rail conditions mean much. Very meaningful for vapor lock, obviously, but not so much the fuel geyser issue.
 
I would love to see someone install a pressure sender on the top of the tank at the cover plate, and a temp sender at the bottom of the tank.
I guess t the rail liquid temp and pressure.
But I'm stopping there.
 
Someone try this who has a garage.

Fill up the tank and park. Grab your portable AC unit and duct the air to the bottom of the gas tank. Crack the filler cap in the morning.

Rinse and repeat with a heater.

Post up what happens when the filler cap is cracked open and removed quickly.

This feels like a YotaMD experiment to me!
 
ramangain said:
Fill up the tank and park. Grab your portable AC unit and duct the air to the bottom of the gas tank. Crack the filler cap in the morning.

Rinse and repeat with a heater.

Post up what happens when the filler cap is cracked open and removed quickly.

This feels like a YotaMD experiment to me!
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Sounds a little like a fire department experiment, like when they deep fry turkeys every Thanksgiving for the local news. :rofl:
 
It'll isolate the gas tank temp as a variable. Gotta decouple things to zone in on a solution, if one exists.
 
Years ago i used a product that was a fiberglass wrap that you wrapped the exhaust with to cut down on the radiant heat. I used it on a jeep i was building to keep some sensitive sensor wires from melting as they had to run within an inch or two of the exhaust. It worked very well and i wonder if you couldn't wrap your whole exhaust from cat down to the beginning of the muffler to help keep that heat in the pipe until it got past the fuel lines and gas tank.

Look it up is called exhaust wrap and it's pretty cheap. I think motorcycle riders use them to keep from burning their legs? You can even touch the wrapped exhaust without getting burned. I think mine baked on and had to burn in so it stuck to the pipe. It smells funny the first couple times you warm up the engine.
 
Brandon Ryder said:
Years ago i used a product that was a fiberglass wrap that you wrapped the exhaust with to cut down on the radiant heat. I used it on a jeep i was building to keep some sensitive sensor wires from melting as they had to run within an inch or two of the exhaust. It worked very well and i wonder if you couldn't wrap your whole exhaust from cat down to the beginning of the muffler to help keep that heat in the pipe until it got past the fuel lines and gas tank.

Look it up is called exhaust wrap and it's pretty cheap. I think motorcycle riders use them to keep from burning their legs? You can even touch the wrapped exhaust without getting burned. I think mine baked on and had to burn in so it stuck to the pipe. It smells funny the first couple times you warm up the engine.
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I've used a bunch of that, works great but only lasts 2-3 years and is NOT for climates with road salt. My exhaust got rusty in a hurry in Phoenix, but was worth the trade off. Now I live where they salt the roads, so I dont need it.

Try ethanol free fuel and see if your boiling issues change for the better. They did on my 80
 
peacesells63 said:
I've used a bunch of that, works great but only lasts 2-3 years and is NOT for climates with road salt. My exhaust got rusty in a hurry in Phoenix, but was worth the trade off. Now I live where they salt the roads, so I dont need it.

Try ethanol free fuel and see if your boiling issues change for the better. They did on my 80
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Good to know! Thank you for saving me that headache.

I've done the ethanol fuel thing. Still boiled at high altitude. Not sure how much it helped in other situations. I had more success getting the scanguage and watching temps while driving. Moderating my speed and gear(while towing) resulted in far less fuel boiling situations despite extreme heat and towing. Still happened but greatly reduced.
 
suprarx7nut said:
Wait a minute. I think there's a fundamental question we need to agree on or discuss.

My assumption/preposition: Boiling point of gasoline is nowhere near any of the temps we've recorded in the 100 series fuel return lines or the tank itself. Boiling point of gasoline is variable, but likely 200F+ (probably closer to 300-400F). Agreed? I see some sources stating boiling point of modern blends is around 300-400F. Way outside of anything anyone here has measured. Boiling isn't the problem, is it? It's vaporization... right? Vaporization happens at a wide range of temps, unlike boiling which you could stop if you keep temp low enough.

The pressure in the tank that activates the gas cap pressure relief is very low. Something like .5 psi. Not enough to significantly change the boiling point or vaporization. The tank really can't take any pressurization.

I think you're coming at this with some assumptions of a pressure cooker or something. It's often assumed and desired to have *vacuum* inside the tank (because the purge system is constantly sucking on the tank when all things are going as planned). Venting excess pressure to maintain near atmosphere in the tank won't change the boiling point (and we're nowhere near it to begin with). You can collapse the gas tank by vacuum force before you have any kind of liquid boiling problem. Even then, the boiled vapors just go into the engine, so no harm, no foul.


Am I alone in this belief?
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I think the 398.7 boiling point is in Kelvin :)

Octane

webbook.nist.gov webbook.nist.gov
 
Eyedaho said:
I think the 398.7 boiling point is in Kelvin :)

Octane

webbook.nist.gov webbook.nist.gov
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That's one constituent of gasoline, but there's a whole slew of other compounds that move boiling point all over the map for the mixture. Octane is about 250F, by itself, apparently, but I think the effective boiling point/range of all different grades and octane ratings really does span that 100-400F range. Probably with a narrower band that covers most of what any of us would get in the US.
 
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