Hey guys - is it normal that high pressure builds up in the gas tank? Every time i go to refuel, which is normally when its about empty, i find there's a lot of gas fume pressure that escapes as soon as i open the tank filler cap. Its like its bloated like a 6 day old whale carcass thats been basking in the sun. Its so much that it has me worried if the tank or a line or somethings going to pop at some point in future.
Pressure build up in gas tank
- Thread starter RustInPeace
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long thread on this. To my knowledge there is no "smoking gun" but some have remedied it with a new charcoal canister, or heat shielding for the exhaust and fuel lines.
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Gas tank building excessive pressure & fuel smell. Dangerous for sure! Why does this happen?
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Eyedaho
SILVER Star
If it's doing this regardless of temperature then I expect something is amiss. Possibly a failed purge valve, but I would think you would get a CEL.
I don’t get a CEL but it does build pressure- it’s real bad at altitude. I can take the cap off, reinstall it and 10 minutes later it’s pressured up again just sitting still.
2001LC
SILVER Star
OM states; Some pressure release when fuel cap opened "is normal". But this is just a momentary hiss, as gas cap released.
Hiss for longer periods, is mostly due to Charcoal Canister (CC) being saturated/flooded. This is most common, in models where CC is in the rear.
Once CC gets, heavily saturated with fuel. We'll often hear, see and or smell fumes in daily driving. Over time, the trapped raw fuel, becomes rancid. Rancid fumes, then smell like gasoline that has sat in gas can for many years. Heat (OAT) and ascending mtn passes, will make more pronounced. But when CC really, badly saturated, even cool days without change in altitude, they smell and hiss. Engine, will even have trouble idling.
CC due become saturated, with use. But that could be a million miles or more. If vehicle always properly maintained.
We must look for what caused the CC to become flooded and correct, before R&R of CC. Or we'll damage the new CC.
Hiss for longer periods, is mostly due to Charcoal Canister (CC) being saturated/flooded. This is most common, in models where CC is in the rear.
Once CC gets, heavily saturated with fuel. We'll often hear, see and or smell fumes in daily driving. Over time, the trapped raw fuel, becomes rancid. Rancid fumes, then smell like gasoline that has sat in gas can for many years. Heat (OAT) and ascending mtn passes, will make more pronounced. But when CC really, badly saturated, even cool days without change in altitude, they smell and hiss. Engine, will even have trouble idling.
CC due become saturated, with use. But that could be a million miles or more. If vehicle always properly maintained.
We must look for what caused the CC to become flooded and correct, before R&R of CC. Or we'll damage the new CC.
Good thinking but the purge valve doesn't apply pressure to the tank, it pulls vacuum
My '06 did this to me 2 months ago while pulling a trailer through the mountains to find a campsite..1st time it's ever happened, wouldn't restart. Let it sit for maybe 30min with the fuel cap off and it fired back up. Could hear the fuel boiling inside the tank. Eventually I'll put some heat shield shield wrap the fuel line.
Eyedaho
SILVER Star
Yes, but it doesn't pull vacuum aka relieve pressure if it's not functioning.
Still not how it works, the purge valve pulls and recycles fuel vapor from the cannister ... does not have anything to do with venting the fuel tank.
What it hot outside / engine working hard when this happened?
Did you just start noticing this recently?
Has any recent service work been done?
Can you monitor your engine cooling temperatures ?
As noted above there is a long thread going on about this and it seems to usually relate to hot temperatures causing the problem but of course can be a number of different things. Extreme cases of this will show folks with gas bubbling back out of their fuel tank filler . My guess is that its EVAP or temperature related
- Thread starter
- #11
THanks for all the replies. And the link to 2001LC 52 page thread on this...
Noticing it the last 2 to 3 months and we've been having cooler weather thru autumn now winter. Only been driving on-road as of late - > no extra strain on engine. Only recent mechanical work last 2 months was e-brake shoes and one rear wheel bearing r&r. Will switch on obd2 scanner for monitoring cooling closer; the temp gauge on dash not showing anything unusual.
Just to be clear you would say its more than just a few seconds of hissing? Under normal conditions a little hiss isn't too strange but if it proceeds for several seconds or more than it makes me think fuel is overheating, not venting, having some kind of issue.
Since the outside air temperature doesn't seem to be a factor, next up is monitoring the ECT like you are planning to do.
What year is your vehicle? I wonder if you could remove the line for your evap canister and see if the symptoms change but IDK I'm just guessing at stuff here
- Thread starter
- #13
Yeah sometimes it hisses for 5-10 seconds. its so pressured that the fuel cap is stubborn to unscrew. 2001. Will monitor the temps closer and look for causes
