jteckmann Posted August 4, 2009 Share Posted August 4, 2009 I have a '86 2.5 w/ the 23gal tank. We've been having unusually hot weather lately (well, what qualifies as "hot" in the PacNW). So it's the first time my MJ's been exposed to 90-100 degree temps on a regular basis. The truck has started venting out a lot of gas when I leave it parked overnight. It's coming from the top of the tank, running down the sides, and leaving a visible wet spot underneath in my gravel driveway. It's my DD, so I haven't had a chance to drop the tank yet and see exactly where it's coming from. But from looking at the truck underneath, I can't find any visible leaks around the filler hose or fuel lines. Truck's been running fine, and I haven't noticed a significant change in my mpg. Is it normal for the system to vent this much in hot weather, or do I have something clogged in the system? Link to comment Share on other sites More sharing options...
Automan2164 Posted August 4, 2009 Share Posted August 4, 2009 Could it be condensation on the tank? Does it actually smell like gas, or just water? Rob L. Link to comment Share on other sites More sharing options...
jteckmann Posted August 4, 2009 Author Share Posted August 4, 2009 It's definitely gas. The odor around the truck in the morning would have you scared to light a match. I tried putting a pan under it one night to get a measurement of just how much was coming out, but in the morning all the gas had evap'd out, and all that was left in the pan was the grime it had carried down off the tank. Link to comment Share on other sites More sharing options...
wallisek Posted August 4, 2009 Share Posted August 4, 2009 I'd drop the tank and inspect the locking mechanism at the top of the tank. The o-ring could be rotten or the cap could be loose. I had the same issue last summer here in the NW with my 01 XJ. Hot days I'd smell gas and the PCM would throw emission error codes. Couldn't find any leaks but slightly damp at the top of the fuel tank. Ended up being improper install by a tech at the stealership a few weeks prior. Locking ring wasn't even tight, just barely threaded on. My fuel pump had died abruptly and it was in the middle of the work week AND I had a full tank a gas. Didn't feel like dropping the tank by myself. Last time I'm ever lazy and take it to the dealer to fix. :fs1: Link to comment Share on other sites More sharing options...
Automan2164 Posted August 4, 2009 Share Posted August 4, 2009 Does the amount of fuel in the tank matter? If it was truely venting, I would imagine it was doing it all day, when it was hot enough to change the volume, not at night when it should be retracting. Maybe it started leaking. Small amount, evaporates during the hot day, but at night since its cooler, and generally parked in the same spot it accumulates? :dunno: Rob L. Link to comment Share on other sites More sharing options...
mnkyboy Posted August 4, 2009 Share Posted August 4, 2009 on my 89 the tank doesnt vent under the truck,the vent lines go into a steel line which goes up under the hood to the canister. yours should be the same. Also the sending unit is on the side of the tank on the MJ so it would be easy to check the seal and the hoses without dropping the tank. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 4, 2009 Share Posted August 4, 2009 Also, directly on top of your tank there are two pressure relief valves sealed to the tank with an O-ring, one valve on each corner of the tank. These valves are hooked to the fuel vent hoses and relieve excess pressure. Check to see that the hoses are attached securely to the valve neck and not rotted off. Link to comment Share on other sites More sharing options...
jteckmann Posted August 4, 2009 Author Share Posted August 4, 2009 Thanks for the tips, guys. :thumbsup: I can see the seal around the sending unit/pump and the leak's not coming from there. But those vent lines you describe, hornbrod, that sounds exactly like where it's coming from. Dropping the tank's a PITA I wanted to avoid this weekend, but looks like that's what I'll be doing. Also - stupid question, but I don't know much about emissions systems - does the evap cannister under the hood ever wear out or get clogged up? Is it possible I might need to change that out? Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 4, 2009 Share Posted August 4, 2009 Here's a pic of where the two valves are on the tank, #3 and #4 Image Not Found Link to comment Share on other sites More sharing options...
wallisek Posted August 4, 2009 Share Posted August 4, 2009 Also - stupid question, but I don't know much about emissions systems - does the evap cannister under the hood ever wear out or get clogged up? Is it possible I might need to change that out? Most older charcoal canisters have a removable filter which can get clogged with dirt and gunk. Pretty common with the older CJ's which causes idle issues. Link to comment Share on other sites More sharing options...
Eagle Posted August 4, 2009 Share Posted August 4, 2009 The tank should never be full enough that expansion in hot weather will cause it to "vent" liquid gasoline. The vent lines to the charcoal cannister are for fumes, not gasoline. If it's pushing gasoline out onto the ground, either there are rust holes below the normal fill level or you're somehow squeezing too much gas into the tank. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 4, 2009 Share Posted August 4, 2009 The tank should never be full enough that expansion in hot weather will cause it to "vent" liquid gasoline. The vent lines to the charcoal cannister are for fumes, not gasoline. If it's pushing gasoline out onto the ground, either there are rust holes below the normal fill level or you're somehow squeezing too much gas into the tank. True, the vent hoses are for fumes, but if the hoses are rotten and the valve is stuck open, or even not secured to the tank?? It shouldn't be doing it, but according to the OP liquid fuel is coming out the top of the tank and running down the sides. I think dropping the tank is in order............ :cheers: Link to comment Share on other sites More sharing options...
Eagle Posted August 4, 2009 Share Posted August 4, 2009 Dropping the tank is definitely in order, because "sumthin' ain't raht." I suspect either the filler hose or the vent hose next to the filler, not the two vents on top. Link to comment Share on other sites More sharing options...
jteckmann Posted August 5, 2009 Author Share Posted August 5, 2009 Tanks again for all the help, guys - especially that drawing. Was able to wedge my hand up in there to feel around, and it's definitely coming from the vent tubes. Can't see what's going on, of course, but the hoses feel brittle & are saturated. So it's probably a combo of rotten rubber, and gas sloshing around in the tank as I drive. Definitely be dropping the tank this weekend. Added: I've been doing a lot of long-distance commuting lately - going through a whole tank of gas in 1-2 days. I'll usually fill up on my way home, so the truck's been sitting with a full tank at night, and my driveway is at a slight incline. That probably explains why it's coming out the top. The filler tube does not appear to be leaking, but it is old. So I'll be replacing all of it while I have the tank down. :cheers: Link to comment Share on other sites More sharing options...
ghetdjc320 Posted September 14, 2020 Share Posted September 14, 2020 Hate to resurrect this thread after 11 years but better than starting a new thread i suppose. Does anyone know the ID of the vent hose that connects to the corner vents on the tank? Also the filler tube ID? Link to comment Share on other sites More sharing options...
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