FJ75 Fuel Boiling/Fuel Tank Leaking Issue

[Letsgocamping]

Hi all,

I've been pouring over search results for this issue, and have read a ton of long threads for 80/100 series LCs. I'm wondering if anyone else with a 70 series has experienced this problem.

The Problem
Last week I drove my Troopy from Phoenix to Flagstaff (~1000ft to ~6800ft elevation), with outdoor ambient temps around 70F. I pulled into a parking lot to grab some groceries, and came back to a large puddle of gasoline under the truck, and an active leak that appeared to be coming from the top of the tank, and spilling down the frame rail onto the ground. I opened the gas cap to a long, sustained release of pressure and some fuel bubbling out.

The "active leak" eventually stopped when my gauge dropped to ~3/4. I am uncertain if there is a hole or rupture in the tank at this point, I've just made it home and plan to drop the tank to inspect.

A Bit of Backstory
A little over a month ago, I had an auxiliary fuel tank from LRA installed in the troopy. On the first drive home from the shop, with fuel in both tanks, I heard a loud POP, which instantly sounded like pressure building up and causing a tank to expand. I chalked it up the new tank and things getting settled, and went about my driving. This loud POP continues to happen intermittently, not on every drive, and has happened across elevations and OATs. I've also been noticing a strong odor of gas fumes inside the troopy more recently. It has had me more concerned, and has been on my list of things to figure out, and now with fuel spilling out of the main tank it has become my top priority.

Initial Thoughts

• Could it be an issue with the charcoal canister?
• Are there other venting mechanisms, either for the main tank or LRA tank, that could be fouled?
• Could the main tank have developed a rust or abrasion hole near the top due to age?
  • If so, the main tank 77100-60300 is no longer produced. Is there a suitable replacement anyone knows of?
• Is anyone else with an LRA aux tank having an issue with pressure/fuel boiling?

I've got more questions than answers right now, but will continue to update this thread with my findings in hopes it can be a resource if anyone else ends up experiencing something similar.

 

[LDowney]

Have you considered that gasoline and diesel (kerosene) expand volumetrically with temperature, at expansion rates over 4 times greater than water?

You outlined that you just added an auxiliary fuel tank so you have have more fuel that is expanding as it warms up. In current conditions it is warming up because you pumped it from an underground tank that is colder than ambient temps, so it is expanding in your fuel tank. In your filled tank; as the fuel warms it is expanding and filling all the remaining voids in your tanks, it will start expanding up the fuel filler neck and out the cap.

Liquids - Volumetric Expansion Coefficients

Volumetric - or cubical - expansion coefficients for common liquids.

www.engineeringtoolbox.com

Before making changes to your charcoal canister, investigating how much expansion space you are leaving in your tank when you fill up might mitigate it for you. i.e., with your increased fuel capacity, you may need to compensate by leaving addition space in your tank for fuel expansion

 

[kgrove]

I had fuel boiling problems on my 100 series a few years back and had to do some reading. The most common culprit was the exhaust pipes warming either the tank or the return fuel lines causing the fuel in the tank to warm up. This usually didn't matter, but would cause noxious smells from my car in Flagstaff if it got over maybe 90F or Phoenix over maybe 115F. For me it was minor enough that the problem was limited to horrible smells in the garage, but others were getting gasoline showers when they'd open their tank to vent.

Since you recently had an aux tank added, look at whether they located the aux tanks too close to exhaust pipes and / or there is inadequate heat shielding. It could also be an exhaust leak. If there is a fuel return line, check whether that gets to close to the exhaust as well (that was the most common problem on the 100 as the fuel return line ran along side the exhaust for quite a ways).

Engine in your troopy? Diesel or gasoline? I would think diesel would have a higher boiling point than gasoline, but thermal expansion is probably similar (just guessing).

 

[Letsgocamping]

Have you considered that gasoline and diesel (kerosene) expand volumetrically with temperature, at expansion rates over 4 times greater than water?

You outlined that you just added an auxiliary fuel tank so you have have more fuel that is expanding as it warms up. In current conditions it is warming up because you pumped it from an underground tank that is colder than ambient temps, so it is expanding in your fuel tank. In your filled tank; as the fuel warms it is expanding and filling all the remaining voids in your tanks, it will start expanding up the fuel filler neck and out the cap.

Liquids - Volumetric Expansion Coefficients

Volumetric - or cubical - expansion coefficients for common liquids.

www.engineeringtoolbox.com

Before making changes to your charcoal canister, investigating how much expansion space you are leaving in your tank when you fill up might mitigate it for you. i.e., with your increased fuel capacity, you may need to compensate by leaving addition space in your tank for fuel expansion

Expansion is definitely a factor. I've been filling to the shut-off point, and not topping off, but it's worth investigating stopping earlier. My main concern is where the fuel would have been spilling from, since it was coming from the tank itself, and not out the filler neck. All the various hoses and hose clamps I could see were dry. Thanks for the advice!

 

[Letsgocamping]

I had fuel boiling problems on my 100 series a few years back and had to do some reading. The most common culprit was the exhaust pipes warming either the tank or the return fuel lines causing the fuel in the tank to warm up. This usually didn't matter, but would cause noxious smells from my car in Flagstaff if it got over maybe 90F or Phoenix over maybe 115F. For me it was minor enough that the problem was limited to horrible smells in the garage, but others were getting gasoline showers when they'd open their tank to vent.

Since you recently had an aux tank added, look at whether they located the aux tanks too close to exhaust pipes and / or there is inadequate heat shielding. It could also be an exhaust leak. If there is a fuel return line, check whether that gets to close to the exhaust as well (that was the most common problem on the 100 as the fuel return line ran along side the exhaust for quite a ways).

Engine in your troopy? Diesel or gasoline? I would think diesel would have a higher boiling point than gasoline, but thermal expansion is probably similar (just guessing).

Excess heat is definitely worth thinking about. The exhaust was rerouted to accommodate the aux fuel tank, maybe I need to look into some heat shielding material.

It's the 3F gas motor in my FJ75.

You've given me some good ideas, thank you!

 

[OGBeno]

Excess heat is definitely worth thinking about. The exhaust was rerouted to accommodate the aux fuel tank, maybe I need to look into some heat shielding material.

It's the 3F gas motor in my FJ75.

You've given me some good ideas, thank you!

What market did this truck come from? Most markets outside of the US did not have charcoal canisters. Yours might not and might be a good addition.

 

[snapdragon]

Check that the petrol(gas) caps are in good condition, even new aftermarket caps can give issues.
Check all vent hozes are in good condition and not blocked.
It will happen unfortunately, but if anything is blocked, it will vapor lock and cause symptoms similar to yours.

 

[coldtaco]

Vents

 

[JuanJ]

Hello,

It appears to be a ventilation problem. Please forgive me for stating the obvious.

Gasoline/petrol fuel tanks have ventilation lines that connect to a port iin the body and to the charcoal canister, if there is one. When one of these is not properly set up, fuel vapors escape.

It is possible that the auxiliary tank you installed has either a missing ventilation line or a misconnected one.

In old age, fuel tank caps let go more vapors than they should. The rear one is close to the rear windows, and somehow fumes find their way through them into the cabin.

Get an FSM and check the fuel lines setup for both tanks.

Make sure the venting line that connects to the body is attached.

Get a new fuel tank cap. Almost all gasoline/petrol 70 Series caps are discontinued. A Hilux fuel tank cap fits; ask me how I know.

Regarding the tank itself, a post-1999 part will fit. Pre-1999 tanks are long discontinued.

If your truck has a charcoal canister, replace it with a later model part. Pre-1999 trucks have the canister on the left side of the radiator. Newer model canisters are bigger (some 6 in. in diameter) and bolt on the left fender apron.

Post-1999 filler necks changed to incorporate an extra valve and lines, probably to reduce evaporation loses. I am not sure if they are a straight bolt-on into older model tanks.





Juan

 

[Honger]

Did you get this sorted?

I had fuel boiling issues due to a catalytic converter I added... removed that and all my ailments went away.

Your exhaust reroute is probably the culprit.