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Excessive fuel tank pressure
- Thread starter MaddBaggins
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There is enough anecdotal evidence that an atmospheric pressure differential at altitude (above your mean fill alt) exasperates this. Heat is going to happen even greater in a Phoenix summer at 117F+ ambient sitting for an hour in a dark green hood heat soaking, yet we don't get the problem until 10k'+ altitude.
To use myself as an example, my truck sits all day long in the blistering sun on a parking lot, and even with 100* F days the engine bay temp doesn't go much (if any) over 130*. I can drive it along in stop and go traffic (which is the worst I've seen so far for my typical driving) and engine bay temps might climb to 140*-150*, and might even spike to 160*, but they rarely hit that high and typically only when idling for long periods of time with the AC on while sitting in the sun. (And turn off the engine or the AC and the temps quickly drop below 160*.)
Freeway driving is more like 100*-120*.
Now if I flog it up a hill with the AC on, where it's under some decent load, the engine bay temp will climb past 160* and stay there. When I was wheeling last weekend, or even driving on the forest service road, the engine bay temps hovered around or above 160* anytime I was going up hill. I'm not sure how far about 160* it got as my fleabay thermostat doesn't go that high, but I know it took a significant amount of time (maybe 3-5 minutes) with the hood open and the electric pusher fan on for it to drop below 160*. That's hot (and not in a good way).
This isn't at altitude either, or at least not a significant one (maybe a 1500' climb and 3000' feet total). But despite that I had significant pressure, enough that it was actually spraying fuel out the filler cap when I cracked it.
When driving around town, you're unlikely to get enough of a load on the engine for a long enough period of time to actually get the engine bay temps that high. The only time I saw the problem last weekend was when I know my engine bay temps were well over 160*, and stayed there for a long period of time.
Anecdotal evidence is just that, anecdotal. The fact that people experience the same problem at 3k feet as well as 10k feet indicates that altitude is not the root cause. Now it can cause the problem to be worse (namely by lowering the boiling point), but that still isn't the primary problem.
I have 30k sitting on the shelf that I'm hoping to put in before I drive into the convention oven that is Grand Junction this weekend. I don't think 20k is overkill. When the whole fan clutch rebuild thing started people were putting in 6k and 10k was going overboard. Now 10k is the norm and there are folks running 24k in AZ.
I figured 30k won't hurt me. Between the SC, the base altitude here, 37s (w/ 4.88s), 1,000+ lbs of accessories, and now pulling a camper everywhere, I can use all of the cooling I can get.
FYI, my new CC does not help with the pressure/boiling issue. However, it helps immensely with the fuel smell. Before I replaced it the fuel smell was almost nauseating. With the new CC, it is hardly noticeable and only eminating from the filler neck. Before it came from the engine bay which affected the in-cab air quality.
FWIW, the heat/boiling gas theory I think is the best theory put forth as affected by atmospheric pressure.
Just my two cents worth...
I am a Missourian and I just returned from a trip to Silverton, Co area. I have never noticed the problem in Missouri and we get hot, not Az hot but hot none the less. I first noticed the problem coming off Wolf Creek pass then just about every day at the higher elevations. The temp on top of passes was probably around 60-70 so not very hot. It seemed to me kind of hit and miss, the smell was first then the if I removed cap I would hear the boiling sound in the tank. Removing cap as has been mentioned only seemed to make the problem worse. It did not happen all the time, but most of the time and usually at the higher elevations (10,000 and higher).
That would be on a 94 fzj80 without aux tank and not always on full tanks. I tried to fill up with half tank and had to wait for pressure to go down.
Interesting...
I am a Missourian and I just returned from a trip to Silverton, Co area. I have never noticed the problem in Missouri and we get hot, not Az hot but hot none the less. I first noticed the problem coming off Wolf Creek pass then just about every day at the higher elevations. The temp on top of passes was probably around 60-70 so not very hot. It seemed to me kind of hit and miss, the smell was first then the if I removed cap I would hear the boiling sound in the tank. Removing cap as has been mentioned only seemed to make the problem worse. It did not happen all the time, but most of the time and usually at the higher elevations (10,000 and higher).
That would be on a 94 fzj80 without aux tank and not always on full tanks. I tried to fill up with half tank and had to wait for pressure to go down.
Interesting...
This makes sense with the heat/atmospheric pressure theory. Ambient temperatures are somewhat negligible as engine bay temperatures far outweigh those of even AZ. Also, although the other guys are mentioning not "high" altitude. Even a gain of a few 1,000' is significant compared to a base altitude of <1,000' which is most of the lower 48.
So take higher ambient temperatures, mix hot driving conditions (passes, stop n go on a hot day, towing, wheeling, etc), and consider the atmospheric pressure plus an additional 4psi in the tank, and you get fuel temperatures that may exceed the boiling point of fuel, but is only realized once the 4psi stored by the gas cap is removed.
I'd be real curious to get a fuel temp in these conditions.
I think next time it happens, which will undoubtedly be this weekend to or from GJ, I will at least get a reading off my gas tank with my IR thermometer.
So take higher ambient temperatures, mix hot driving conditions (passes, stop n go on a hot day, towing, wheeling, etc), and consider the atmospheric pressure plus an additional 4psi in the tank, and you get fuel temperatures that may exceed the boiling point of fuel, but is only realized once the 4psi stored by the gas cap is removed.
I'd be real curious to get a fuel temp in these conditions.
I think next time it happens, which will undoubtedly be this weekend to or from GJ, I will at least get a reading off my gas tank with my IR thermometer.
So I took an extra temp gauge I had laying around, and attached it to the fuel line. Used some pipe insulation I had laying around to wrap it, hopefully to insulate it so that all I get is a measurement of the fuel line temps.
So far the results have been interesting. Only driven it about 5 minutes, but it was kinda surprising to see the temps climb. They went from (roughly) ambient to about 115* in that 5 minutes.
It'll be interesting to see what the temps do over the next few days. Maybe I should use this as an excuse to go wheeling so I can "test" it better....
So far the results have been interesting. Only driven it about 5 minutes, but it was kinda surprising to see the temps climb. They went from (roughly) ambient to about 115* in that 5 minutes.
It'll be interesting to see what the temps do over the next few days. Maybe I should use this as an excuse to go wheeling so I can "test" it better....
'Junction is a venerable tepid paradise compared to the hellhole of Phoenix in July/August.
So I took an extra temp gauge I had laying around, and attached it to the fuel line. Used some pipe insulation I had laying around to wrap it, hopefully to insulate it so that all I get is a measurement of the fuel line temps.
So far the results have been interesting. Only driven it about 5 minutes, but it was kinda surprising to see the temps climb. They went from (roughly) ambient to about 115* in that 5 minutes.
It'll be interesting to see what the temps do over the next few days. Maybe I should use this as an excuse to go wheeling so I can "test" it better....
Sounds like a most excellent excuse!
It'll be interesting to see what the temps do over the next few days. Maybe I should use this as an excuse to go wheeling so I can "test" it better....
This morning engine bay temps were below the fuel line temps. The fuel line temp did not climb until the engine bay temps were about 15* higher than the fuel line temps. Once engine bay temps were higher than the fuel line temps (which took a while as I hopped on the freeway almost immediately) the fuel line temps started climbing.
The fuel line temps stayed right around 10-15* below engine bay temps the whole time.
The coolant temps were already warmed up well before the fuel line temps started climbing, so I don't believe that was as much of a factor as the engine bay temps.
Sounds like a most excellent excuse!
Indeed!
"Honey, I need to go wheeling next weekend so I can see if I can boil some fuel."
So no wheeling yet, but I've already seen the fuel line temps hit 125* F.
That's with relatively low load, and just driving around town. Engine bay temps were around 140* F, which are about normal for around town driving.
Assuming engine bay temps could get as high as 175* when wheeling, under heavy load, etc, that could put the fuel line temps at 150* or higher. It would take some time for the entire fuel tank to heat up to that level, but that would easily explain the boiling fuel.....
Something else to consider is that the fuel return line dumps into the tank approximately 2" from the fuel pump intake/sock filter. So the heated fuel doesn't get much chance to mix with the rest of the tank and cool down before being sucked back into the pump. This could be exacerbating the problem.
Indeed. I didn't even think about that, but that makes perfect sense.
Was doing some more research and ran across someone with an ATV that had the same problem. Here's how Yamaha addressed it:
It wouldn't be that hard to pull the pump assembly out of the tank and bend the line to dump the fuel outside of the baffle box that the pump sits in. This would allow the warm returning fuel to mix with the cooler volume of the rest of the tank before it made its way back to the pump.
Looking back at my video of the gas tank, you're absolutely right. The baffle box would largely prevent the hot return fuel from mixing with the cooler fuel.
Wondering what down side there would be to that, however. Mr. T must have designed it that way for a reason.
Also, that wouldn't solve the problem but would only delay it at best. Eventually the entire gas tank would be hot enough to get the fuel boiling. For short term, it would definitely reduce the fuel line temps as you'd be starting off with cooler fuel from the start.
Heat
The heat explaination makes perfect sense. A good example is simply putting a gas can in the sun and one in the shade. The one in the sun will build up more pressure. This used to happen all the time when I used to play in the sand dunes. They used to expand a great deal in the day. Once they cooled at night they would not have as much pressure.
The question that makes me nervous. Is the system designed to handle this pressure and does it effect performance or can it cause a major failure?
Is this a new problem or the condition of an aging vehicle that needs some of the components replaced or maintained better to run as intended(cc, fuel lines, regulators, injectors, etc. )
The heat explaination makes perfect sense. A good example is simply putting a gas can in the sun and one in the shade. The one in the sun will build up more pressure. This used to happen all the time when I used to play in the sand dunes. They used to expand a great deal in the day. Once they cooled at night they would not have as much pressure.
The question that makes me nervous. Is the system designed to handle this pressure and does it effect performance or can it cause a major failure?
Is this a new problem or the condition of an aging vehicle that needs some of the components replaced or maintained better to run as intended(cc, fuel lines, regulators, injectors, etc. )
My question exactly - is this a new issue just coming to light, or is is something that has been discussed before when the vehicles were only, say, 11 years old... Does not seem like anyone was aware of issue prior.
I don't think it's an issue for 99% of situations. Driving around town, or even longer distances on the freeway, fuel line temps mostly sat at around 40-45* C with a brief spike up to 50* C (engine bay temps had spiked to over 70* C). Fuel line temps do seem to follow engine bay temps, so you cool your engine bay and you cool your fuel.
It was interesting to watch the fuel line temps follow the engine bay temps. I don't have much doubt that the two are related.