LRA aux tank and slight gas smell

[BlackMammoth]

I have had fuel boiling issues before skids or LRA tank. Summer heat + offroad up 7500' mountain = guaranteed fuel vapors pouring from gas cap area. I was concerned the first time it happened but a quick check on this forum showed it as quite common.

 

[BlackMammoth]

My assumption is that one would stop, the vehicle at elevation intervals, turn off the vehicle, carefully bleed pressure from the gas cap, restart, and carry on your merry way. Is this correct and wise?

The pressure doesn't build up - it's vented. My guess is that there is a pressure release valve somewhere. You can see / smell and hear the fuel vapors escaping from the fuel filler area (this was when everything was stock).

 

[bloc]

Regarding fuel boiling, other than ensuring there are not heat sources near fuel tanks/line, not skid plates/etc covering tanks, and potentially placing a fuel cooler on the fuel return line, what can the stock or modified LC owner do at elevation, on really hot days, or hot days + elevation to control system pressure for safety?

My assumption is that one would stop, the vehicle at elevation intervals, turn off the vehicle, carefully bleed pressure from the gas cap, restart, and carry on your merry way. Is this correct and wise?

Venting reduces tank pressure and increases boiling rate. The boiling eventually stops because usually no more heat is being added to the system and the very process of boiling takes heat out of the fuel in the tank.

The only real solution is reduce heat going into the tank, which is where a cooler could help. I’m personally reluctant to add potential points of failure to an otherwise super reliable fuel system though.. at least for an otherwise stock rig that has an annoying problem but isn’t technically very dangerous.

Then again I haven’t killed an evap canister yet like some here have at Moab. Or dealt with the issues you have.

The pressure doesn't build up - it's vented. My guess is that there is a pressure release valve somewhere. You can see / smell and hear the fuel vapors escaping from the fuel filler area (this was when everything was stock).

The issue is the vent can’t handle the rate of evaporation.

 

[TeCKis300]

Regarding fuel boiling, other than ensuring there are not heat sources near fuel tanks/line, not skid plates/etc covering tanks, and potentially placing a fuel cooler on the fuel return line, what can the stock or modified LC owner do at elevation, on really hot days, or hot days + elevation to control system pressure for safety?
My assumption is that one would stop, the vehicle at elevation intervals, turn off the vehicle, carefully bleed pressure from the gas cap, restart, and carry on your merry way. Is this correct and wise?

That's a good question.

It's going to be those long hot crawling days, combined with elevation, that's most likely to heat soak and cause these types of issues. Some of it to @BlackMammoth point is that it's expected to a degree for extreme conditions. Other threads have suggested higher octane fuel that typically has incrementally less vapor pressure. The question is whether each factor is enough, as it all adds or helps the situation.

Pressure does build in the system though in situations. To mitigate vapor pressure and potential boiling for situations like significant elevation. It has a limit. The gas fill cap is the actual pressure safety device. Again, don't vent as that'll potentially make the situation worse. Others have said not to fill past 3/4 tank to minimize liquid fuel from boiling out.

So what can be done? Anything that helps under chassis temps and airflow. Maybe don't idle the car excessively when stopped as that builds heat. Think of it as a system and sometimes even maybe a front bumper could change airflow characteristics enough. May not be a single magic bullet.

There's a heat barrier product that I've used around my LRA tank near the muffler.

Amazon product ASIN B000E243AW

 

[porkandcorn]

There's a heat barrier product that I've used around my LRA tank near the muffler.

another solid idea going on my list, which i'll be sure to post both here and on my 100 forum post on this topic once this has all simmered for a while.

 

[porkandcorn]

how about adding octane boosters on hot climbs?

 

[BlackMammoth]

Back in the 90s I used to buy Toluene in 40 gallon drums and mix several gallons into each tank of fuel. That was an effective octane booster.... If you are talking about those little plastic bottles in the auto parts store - don't waste your money.

Now I use Methanol injection and get similar results without having to deal with the difficulty of buying large amounts of solvent.

For me, the landcruiser just eats 87 octane fuel - I am not going to try to shift the boiling point by altering it.

 

[grinchy]

Have you replaced the gas cap / gas cap oring @porkandcorn ?

 

[porkandcorn]

Have you replaced the gas cap / gas cap oring @porkandcorn ?

that's on my list of solutions.

 

[bloc]

Plus that small bottle of octane booster won't appreciably change the boiling point of the larger tank of fuel, which is a major factor in all of this.

 

[Fisher23]

The pressure doesn't build up - it's vented. My guess is that there is a pressure release valve somewhere. You can see / smell and hear the fuel vapors escaping from the fuel filler area (this was when everything was stock).

There is a valve that opens and vents the tank to the atmosphere when the engine is turned off. This is to release the pressure so that one can easily remove the fuel cap to re-fill the fuel tank. When the engine is running the valve closes and opens to maintain a set pressure.

Sometimes this valve can "stick" .. which is why I earlier suggested stopping the vehicle, turning off the engine and then checking if the gas cap when removed was holding any pressure. If there is pressure when the fuel cap is removed and the engine turned off then there is something wrong with this valve.

I know about this valve from trying to figure out why I have been occasionally getting codes.

 

[porkandcorn]

There is a valve that opens and vents the tank to the atmosphere when the engine is turned off. This is to release the pressure so that one can easily remove the fuel cap to re-fill the fuel tank. When the engine is running the valve closes and opens to maintain a set pressure.

Sometimes this valve can "stick" .. which is why I earlier suggested stopping the vehicle, turning off the engine and then checking if the gas cap when removed was holding any pressure. If there is pressure when the fuel cap is removed and the engine turned off then there is something wrong with this valve.

I know about this valve from trying to figure out why I have been occasionally getting codes.

This is exactly what my Toyota mechanic suspected was going on, and causing my fill issues. My head has been clogged with so much information that I *almost* understand, that I'm forgetting some things.

So the question is - what conditions can cause this to stick, and what is the solution to guarantee it's not sticking? What is it about adding an extra capacity tank that makes this want to stick? Is this as simple as a part replacement? Or some kind of tuning of this valve?

 

[porkandcorn]

I have had fuel boiling issues before skids or LRA tank. Summer heat + offroad up 7500' mountain = guaranteed fuel vapors pouring from gas cap area. I was concerned the first time it happened but a quick check on this forum showed it as quite common.

Yeah, freaked me out too last Summer - my first time. I was sure that if I hadn't stopped, we'd have exploded. That said, it took 20 minutes to depressurize my fuel system through incrementally cracking the gas cap open as not to scald myself. I could hear the fuel tank's metal creaking and popping as it returned to size. The vapor escaping was too hot to even put your hand over. I suspect I had a rather nasty case of this relatively common problem. I was told by my Toyota mechanic that the tank expansion could have been so severe as to potentially create microscopic cracks that could leak to weld degrades/EVAP codes over time. I have a video of the event.

 

[Tex68w]

So is this issue exasperated with the LRA?

 

[porkandcorn]

So is this issue exasperated with the LRA?

(Bear in mind I have a 100 series and unwittingly hijacked your 200 forum). From what I hear, the most vexing LRA issues are with 100 series AFTER the late 2004 evap system redesign. It's hard to determine, but from my experience, the answer would be yes. I have venting issues that are endemic with the LRA system. Venting issues, I suspect, restrict the normal flow of gases in the system in the way Toyota designed it. I never had fuel boiling on Mountain passes in the Summer in Utah, until AFTER the LRA tank was installed and I began having vent/fill issues. Extra on-board fuel means extra vapor, any way you shake it.

 

[Tex68w]

Makes sense, that's a bummer for the system. Hopefully they can come up with a larger vent that works in conjunction with the tank to alleviate this issue.

 

[Fisher23]

This is exactly what my Toyota mechanic suspected was going on, and causing my fill issues. My head has been clogged with so much information that I *almost* understand, that I'm forgetting some things.

So the question is - what conditions can cause this to stick, and what is the solution to guarantee it's not sticking? What is it about adding an extra capacity tank that makes this want to stick? Is this as simple as a part replacement? Or some kind of tuning of this valve?

If you turn off the engine and the tank or gas cap is under pressure then this evap. valve is not working or the evap lines are hooked up wrong.

Now it is important that when you installed the tank you maintained the "green" lines which vent to the atmosphere.

If you attached the green line to the fuel filler you will have an issue that could cause that problem of over pressure and not releasing the pressure as there is no escape for the pressure then. This will also cause filling issues.

So I would take a good look at how it is hooked up first. Make sure that line from the canister vents to the atmosphere for pressure relief. Then if it is hooked up "for sure" correctly then it's likely the valve.

Did the issue start immediately after install? Then I would check that line in green on the diagram carefully.

Diagram by grinchy (back a few pages)

 

[porkandcorn]

Did the issue start immediately after install? Then I would check that line in green on the diagram carefully.

Importantly, the system worked great, with no issues, and after each of my 3 separate installs for the first OEM/LRA tanks fills, and through the first tank of gas. The issues always seemed to begin on the 2nd tank fill. I will check the connections carefully on this next round, but it sounds like the valve is the issue - but only after burning through a tank of gas in the OEM tank, and from what my last mechanic said, it may be related to a slowly-saturating canister. Which came first - the chicken or the egg! Now I'm getting a headache

 

[porkandcorn]

So I'll ask the group again - if this valve is suspect, what part assembly can be put in to replace it? So that at least I can rule out some kind of mechanical failure of that specific valve?

 

[TeCKis300]

I think there's some things that maybe useful to clarify.

1) A normal operating fuel system should generally not see the fuel boiling. Other than the extreme elevation and crawling situation. Outside of an installation error, this would suggest there's a thermal management problem under the chassis where more heat than normal is finding its way into the gas tank. Consider radiator airflow and fans at the grill, to airflow under the vehicle. And exhaust heat sources, including the muffler proximity to the aux tank, and muffler tip pointing. I know in the 100-series, later model years removed an aux condenser fan, so it's possible there's more likelihood of heat soak at idle and low speeds.

2) Evap system is to absorb normal fuel vapors. It's not designed to handle excessive boiling vapors. The root of boiling is not because of an evap system fault, see #1. The evap system is normally open to atmosphere during engine operation to equalize vacuum from fuel being drawn down. It will also cycle depending on vapor pressure. Into building pressure to suppress vapor pressure and boiling. If the system is constantly under pressure and preventing fill, again, look at #1

3) The whole system has a detailed self check. If there's a VSV failing, you would know it by way of check engine light. If there's a CEL, lookup the code and it should give a better clue of what to diagnose. The main VSVs are the purge valve and breather valve.