Fuel smell - filler neck gasket?

Hey all, I've been chasing a fuel smell that happens when I fill my tank. After searching on here, I checked out my sending unit but it appears to be pretty new. It's bright white with no signs of cracks (most of the cracked ones in the posts seem yellowed). Yesterday I took off the inner fender liner and it looks like the gasket between my filler neck and tank may be leaking. What is the consensus of the 996 smarties? Is this an easy job? Is there a write up? I was going to order a gasket for my sending unit while I'm at it but would love any of your thoughts.

I would smoke test and verify before i would go after that gasket. I think u would have to drop the tank.

Quotes source post: 19960634

Is there a way to diy a smoke test or do I need to go to a shop?

If you�re willing to spend a little bit of coin to purchase a smoke tester, it can be a diy. The smoke machine is a great investment, and there are tons of bargain options available now. It�ll pay for itself after a single diagnostic. It is very useful for checking for vacuum leaks - those pesky little issues can snowball into huge problems.

I have this one. They range from $50-$200. Amazon Amazon

Quotes source post: 19961320

Oh that's awesome, thanks so much!

Okay, so next question... I just ordered the smoke machine. Where/how is the best place to hook it up to check the fuel evap system for leaks?

Put the ruber plug into the fuel fill......if that doesnt seal zip tie a rubber glove on the fill neck, cut finger, zip tie smoke machine tube into finger.

Did you find resolution? I have same symptoms. It appears to be the actual tank leaking at the interface of the neck plastic and the main portion of the tank. I don't know if this can be resealed or is a new tank is needed, but I am not certain as I have not found anyone else that had a leak here. FYI: Smoke will only work for this test if the fuel level is below the leak area.

Quotes source post: 19982708

I have not yet. I plan to smoke test it tomorrow and will post an update hopefully.

Alright, I finally had a chance to hook up my new smoke detector. Murphy's law, it has a great funnel press fit setup, but it wouldn't sufficiently seal the gas pipe. Nor depress the anti siphoning flap on the fuel filler neck. So I rubber banded a rubber glove onto the unit with less than amazing results... I did not see any smoke leaking out of the tank gasket that I suspected earlier in my thread. Nor did I see any leaking out of the fuel pump, nor under the battery area. Best I could see is smoke leaking out fo the vent valve. Here's a video if anyone is willing to check it out. https://photos.google.com/photo/AF1Q...c2eix6tqV-6U78 Would this cause my fuel smell? To clarify, I have no issues filling my tank with gas. No check engine light. no hesitation or any kind of issues... Just the fuel smell

That would deff cause a vapor leak and what i would fix next. It may not cause a code because it may close and the leak might be on the other side when it tests?

Quotes source post: 19986380

Hi, any chance you could check the link for the video, its not working for me. Is the leak from the small blue valve? I have replaced that foam gasket on the filler neck. Easy to do, but not the culprit. I only get fuel smell if I fuel above 3/4 tank. As soon as the level drops, no smell. No evidence of fuel leaking other than smell ie no drips. Have been all over the tank with borescope, all covers off, found zero leaks. No codes, no problems fueling. Also looking at those smoke machines, which model would you recommend? Looking at Autool SDT106. Cheers, Jools

Yea i could not get the link to open either.

Sorry, apparently I had to do a public link. Try this. https://photos.app.goo.gl/YxRfJjio91m51gmv5 I went ahead and ordered this part, the vent valve. As others have suggested (I posted this in a few Facebook groups). If it's leaking smoke, it's leaking vapor. I was surprised because I thought there would be an engine code, or problems filling the tank. But at least one other on the FB group said he had the same issue, replaced this part and it fixed it. He also had no codes and no problems filling his tank. I will post an update next week when I install the part and try my first fill up. I just ordered this smoke detector. Amazon Amazon I've used it once and if it finds the culprit, it was worth the $70 by saving my time and trip to a shop. A few things I would note, I also had to order smoke fluid which did not come with it. Another $20? It's not variable pressure so you can only run it for a few minutes or apparently you run the risk of creating too much pressure in the system and damaging parts. The cone in the photo fits in the gas filler (circled in red). However, it did not seal well enough nor have any way to open the siphon safety flap. So it was in a sense useless. I ended up using a rubber band to seal a rubber glove over the filler, and another rubber band to seal the hose into the glove. Not ideal, but it worked. If there were a model slightly higher with a better cone, or that included the smoke fluid I would have chosen that one.

Thank you Dan, that is super helpful. I can't quite get my head around why there would only be leaking vapors above 3/4 tank (have no smell if I only fill to 1/2 tank) but its absolutely worth a shot. I have ordered a smoke machine, plus fluid. I ordered the Autool SDT202 as it has a bulb on the end that I hope will inflate to fit the filler neck. It doesn't take much to get me to buy something that's useful for the workshop.

That cone will come in handy for testing intake system leaks. It seals well when inserted into intake hoses.

Quotes source post: 19988063

When u do your smoke test u should pull the battery and the cover over the sender (if a c4 then no need to pull the bat). U should inspect the sender very carefully. Here was mine and somehow it melted but i only smelled fuel when i woulds fill up and it never leaked.

Quotes source post: 19988156

I have a cabrio. Yes, I pulled the top hat in the frunk previously and yesterday when I smoke tested. My sender is not yellowed like this, it looks relatively new. I've looked very closely and I don't see any cracks or signs of leakage.

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Thanks. I did pull all the covers off when looking for the 'leak'. I noted the previous owner had replaced the fuel sender/filter/pump. Have seen exactly the same burn/melting on my old Range Rover L322!

Quotes source post: 19988063

My thought would be... Fuel produces vapors. More fuel = more vapors? More vapors with a smaller place for them to go (because the tank is full). Meaning the car would more likely push those vapors out of any leaks when the gas tank is more full.

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I'll buy that, makes sense. Keeping my fingers crossed. Will report back.

Quotes source post: 19988184

Vapor pressure is primarily a function of temperature. More fuel in tank does not cause increased vapor pressure. If only when tank is mostly full (as I just went through), you will find liquid is above leak area. I diagnosed by filling tank, then pressurizing using smoke machine (with smoke off); look for wet spot on tank and lines. As a point of data: Mine leaked at the plastic to plastic interface of the filler neck flange to tank body. I suspect age as this happened over winter storage. I attempted to use plastic tank repair epoxy which seems to be working, but due to the tank material, longevity is certainly questionable.

Quotes source post: 19989350

I suspected this joint on mine also. My smoke test showed no signs of leakage at that joint however. I did do the smoke test with a nearly full tank. But I would imagine that even with a nearly full tank, the gas would not be sitting above this joint. So a leak should have showed... But much to your point. When I suspected this joint of leaking I could not find any forum posts on how to replace it.

Mine was not obvious with smoke, but very obvious with fuel level above filler neck input and small amount of pressure. With a full tank, I had liquid exiting the leaking neck interface. As far as not finding much documented on this leak, I suspect age related. If so, more will be seen, which unfortunately means if my repair does not work best option is a new tank.

I�ve spent many hours trawling the internet for help on this. I found a thread on here (I think but possibly 6speed) where the guy pulled the tank. Not easy because like me he was blessed with AWD. He pressurized the tank with water and couldn�t find a leak. Another forum member did supply him with a new tank which was fitted and eliminated the smell. IIRC he�d changed other valves etc in the diagnostic phase. I agree that we�ll probably see more of these as our cars age. The photo above of the filter neck/tank joint and the wetness could�ve been taken from my car, exactly the same. For now I�m basking in the (possible) fallacy that the filler vent valve replacement will cure all. Of course, my likely future is one where I can�t fill my tank above 3/4 unless I�m on a driving trip

Quotes source post: 19989932

I suppose the good news for you is... We seem to have the same symptoms and I'll be replacing my vent valve next week hopefully. You'll soon have a guinea pig's answer for you. If this doesn't work and we have to try replacing the tank to filler gasket, I'm gonna tag you in as the next stage guinea pig. Deal??????

Deal! Happy to brain storm and try new stuff. But... After looking at the pictures from the guy that removed his tank (with a 4 post lift) that's not in my cards. I'll live with 3/4 tank fill ups.

Quick update... So I've always had this strong fuel smell when my tank is full. My pump on the top of the tank looks newish, no cracks or issues there. I thought my leak was the filler neck to tank connection but earlier in this thread, i was recommended to smoke test the gas tank. That showed the breather valve leaking. So I replaced it. It's super easy. Lift the car up, take front right wheel off for easier access. Take out the fender liner (though it doesn't need to be completely removed). The breather valve has 2 easy hose connections. Squeeze to remove. remove the one 10mm bolt in the filler neck area then that allows the silver mounting bracket to move so you can access the 2 10mm bolts. What I did learn though is that the REED Valve is often overlooked. check out this thread, this photo. https://rennlist.com/forums/996-foru...-gas-tank.html this valve is often overlooked. It tucks into a slot on the new breather valve. If you do not install this (I missed it), you will not be able to fill the tank properly. The pump will constantly kick off. But... this has solved my fuel smell issue! figured I'd post an update...

Congrats, that is awesome! I bought the smoke tester and preemptively a new breather valve. Unfortunately I haven't been able to set some time for testing. It's going to be at least another couple of weeks. When I took the filler neck out to make sure it was seated correctly I became aware of the reed switch. Slippery little sticker for sure! Thank you for the update, is given me hope! Will report on my findings in due course.

Sooooo, finally got some time to smoke test my car. The body of the breather valve released some wisps of smoke. Yes! Valve replaced; I'd pre-ordered one based on Dan's resolution. Smoke tested the new valve, no smokey wisps. Filled with fuel, left overnight in the garage to be met the next morning with the same fuel smell. *****. I've driven it to below 3/4 tank and as previously the fuel smell has gone. So I've replaced a valve that was leaking but I've still got the smell. I'm going back to 10 gal refuels. You win some, you lose some. I'll keep monitoring to see if anyone else comes up with a fix.

Did you check the O-ring on the gas cap? Over the years I've owned my 996, I've been through 3 gas caps.

Quotes source post: 20033978

I did, one of the first things. Appreciate the thought though. It emanates from inside the wheel well. No codes ever, never runs oddly, never problem fueling. Only when fuel is above 3/4 tank, not related to when it was filled, only the level.

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See my post above on tank neck interface; remove the fender liner to inspect. Mine had same problem only when full.

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Yeah... Life has been crazy here. I originally updated that the breather valve fixed the smell, but it didn't. I feel like it's better, but it's not gone. It's probably not fixed because I posted on here that it's fixed. Car Karma... When life settles in the next few months I'll try the smoke test again, but on a nearly empty tank. Sorry to have you replace the breather valve on my word, but it was probably due anyways. And it's an easy job.

Quotes source post: 20034058

Completely agree. I always thought this was the problem but it was nice to dream for a while. There is some evidence of wetness around that area. I can't think that there's any way to successfully reinforce/seal that joint without removing the tank. I've no intention of doing that unless I ever get the urge to convert from C4S to C2S. I will remove the liner and spray some Gunk or other engine cleaner and thoroughly clean that area to see what we're dealing with. Its always looked grubby so I don't really know what kind of issue it has. I've never seen a leak on the ground or in the underbody panels.

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No worries on the valve replacement, it was leaking. Like you, I think the smell is reduced. I did re-test it will an empty tank and saw nothing, zero leaking around the filler joint but I still highly suspect that is the issue.

Quotes source post: 20034471

I did repair mine without removing the tank. Unknown if it will last. Here is what I used: Blue magic 6522KTRI plastic tank repair kit. As there are numerous reports of leaking tanks at the neck interface, is suspect these are aging out and costly new is the only other option.

Quotes source post: 20035327

Smell is gone? How did you get access to apply the BM? I couldn't reach the joint through the hole in the wheel well, same from top.

Remove the fender liner and Filler tube. Insert hand. Ignore pain from lack of clearance and strained fingertips. Clean with brake clean. Clean with brake clean again. Clean with brake clean for a third time. Sand. Sand. Sand. Epoxy. Yes, smell is gone. Once I opened up and cleaned, I found visual signs of dark spot where damp with gas. Wiped away and dark spot would reappear and migrate. Do this to be certain where your problem is. Never guess on repairs.

Thank you! It seems many years of working on Harriers with my hands in very tight spaces has led me to this car. Will report back.

Well, its done, fixed. The fuel smell is no more. Used the Blue Magic 6522KTRI plastic tank repair kit sourced from Amazon. Went overboard on the prep, let it cure for a week even though thats not required. Filled up yesterday and this morning there is clean air in the garage. Thanks to everyone above who helped.

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Are these photos of the same location? The bottom of the fuel filler neck into the tank? Was the filler neck hard to remove? Any tips or tricks? I'm gonna have to try this sometime this summer...

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Yes, same location. Filter tube is straight forward to remove, especially as you have already removed the breather valve previously. Once that's removed you just wiggle and pull the tube out. Access is a little tight. I just mixed then applied the sealant in quadrants as there wasn't enough space to manipulate and apply around the entire circumference at once. It's so satisfying to have this fixed.

Quotes source post: 20074768

Great to know! So basically there was a small crack at that filler neck area? Clean, sand, clean and fill? Did you replace that rubber/foam gasket at the bottom of the filler neck? My sense of smell is pretty bad, but my wife noticed my car parked in the garage with a full tank again yesterday...

Yes, micro crack/s at the seam. Couldn't see any cracks, just wetness. You've nailed the process. I'd previously replaced that foam gasket thinking it was the source of the leak initially. The one I took off was perfect, no evidence of any leaks or breakdown of its integrity. There was no doubting the smell from mine before the repair! I suppose, once they crack the smell will only get worse over time.

Quotes source post: 20075326

Sounds great, thanks for sharing it all! I hope I can do this sometime in the next month or so...

Hi all, I've had the fuel smell coming from in/around the front right (filler side) for 7 months. I've had it smoke tested by a couple of independents with nothing visible. No codes either. Today the indie said the charcoal is fine, the valves are fine but looking at the tank it has a stain (petrol smell) coming from around where the neck inserts into the tank. Not the best photo but you can see the patch and it runs up towards the neck which is unseen. Smells of fuel. So dropping the tank and we'll soon see I guess.

Quotes source post: 20137402

JustinbAUS No need to drop the tank to fix this. You've gone the route of several of us and the fix is doable with the tank in-situ. Mine is still odor free after repair. See above. JB

For what its worth had same issue on my car. Gas would seep through the seal where the fuel filler neck meets the fuel tank when tank was >3/4 full. not the most economical but ended up replacing the tank and filler tube. no more gas smell