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Faint odor of avgas in RV-9

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don.olandese

Well Known Member
for the second time in a couple of weeks, I experienced a faint but noticeable odor of avgas in the aircraft. in both instances, it lasted maybe 30 seconds, and wasn't real strong. nevertheless, even without the wife's excited comments, it was disconcerting. after the first one, I looked the airplane over both inside the cockpit and outside, but found no indication of a leak anywhere. then it recurred again today. both times, I BELIEVE the odor occurred at or immediately after an adjustment to the mixture control, tho I cannot fathom why that would be the case. anyone with similar experience or suspicions? don olandese
 
I had similar. Eventually traced it to a fitting at the back of gascolator. The smell was more pronounced with aux fuel pump running before engine start. Tightened the fitting no more smell of gas in the cockpit. Yours might be different but I suggest checking in/out sides of the gascolator. I never liked the thingy. Some day I will get rid of it.




 
Check all of your fittings, look for blue stains.

Also, check the vent lines and their fittings. They are another source for fuel smell.

Finally, check around the shaft of your fuel selector. Mine had a minor weep once upon a time that was noticeable by the in-flight smell.
 
thanks guys

have done most of that but will do it again more thoroughly. you have given me some ideas to focus on. these kind of minor and transitory things are the most frustrating to deal with, but then a possible fuel leak is not one of those things we should blithely ignore....
 
leaker....

Hello, here are a couple places to check. I've found leaks in the following places - fuel selector O-rings (been rebuilding them quite a lot lately) - small defect on the firewall fitting that would only show up in a blue moon - fuel sensor gaskets in the wings... usually quite a lot of blue stain there - weeping external rivets on the fuel tanks, a temp fix is wicking locktite on the rivet head with a slight suction on the tank until you can fix it properly. Best of luck!!
Brian
 
Someone posted on here a while back to put white paper towel or tissue around all the fittings, go fly for a bit (try and replicate what gave you the smell) then see if any of the white tissues are stained blue.
 
Mine was a minor weep on a wing root fuel filter. Does not have to be in the cockpit.
 
Have you checked the fuel vent line fittings? Early on, I had that faint 100LL odor and finally found that the vertically oriented nut on the AN833-4D elbow fitting that passes through the right side F-902 bulkhead had a minor leak. I felt some "greasy" residue on the bottom of the elbow and it was blue. I tightened the nut a bit more and that took care of it.

I had a few gallons of fuel in each of the tanks for testing the fuel system, first engine start, etc. but the leak did not reveal itself with odor at that time. With much more fuel in the tanks, the fuel vent lines will take on fuel. Not sure how, maybe vapor condensation overnight, or splashing during flight, or both. Sometimes it will spew out of a vent just sitting there after a few days of not flying.
 
Fuel Level Sender

Had the same symptom. Faint smell of avgas when I got in the plane. Removed the wing root fairings and discovered it was the fuel level sender and another tiny weeping leak around the bottom of the tank cover found using the white tissue trick.

Drained the tank, removed and resealed the fuel level sender and a applied a healthy fillet of pro seal to the perimeter of the tank cover.

No more leaks - confirmed with the tissue trick.
 
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carlrai said:
Had the same symptom. Faint smell of avgas when I got in the plane. Removed the wing root fairings and discovered it was the fuel level sender.
Drained the tank ....resealed the fuel level sender and a applied ... fillet of pro seal to the perimeter of the tank cover.
.
Click to expand...

Yep ...this was my experience exactly. when I loosened the wing root fairings from the bottom side, I could see some blue stains around a few of the screws in the sender cover. No trace of blue stain on the intersection fairing or exterior surface. Hard to imagine how clear the odor was in the cabin for such a tiny leak. Leak fixed .... no more odors. :D
 
thanks again!

some of this stuff I would probably never have thought of! research begins this evening, when the temp drops below 95! will broadcast whatever i find, for thread closure, tho it may take longer than tonite.
 
My experience,
if you smell it then it is there even if it is very hard to find it.

If you have Andair fuel selector valve make sure you have stake the tiny screws. I had missed that but was able to do it in place. Also just like, had a faint smell of fuel once in a while under a certain condition. It end up being from the wing root area on the tank. Tightened the screws a bit and no more smell since.
 
check the wing root

Me too... had a leak last month at the bottom of the access panel on the tank. I smelled it in the cockpit after landing.
Seems like this is pretty common recently!

I've had the tanks off to fix various things 5-6 times, I think! It is one of the jobs I hate the most and makes me want to kill whoever thought it was a good idea to bolt the tanks on through the spar.

This time, I'm not using the cork gasket again. I've learned my lesson and am just going to proseal the panel on and hope it never leaks again.

I was also surprised at the blue staining around the fuel sender gasket (Princeton capacitive probe). I guess I'll tighten those bolts a bit more.
 
My experience with fuel smell in the cockpit was traced to the Andair fuel valve. It seems they had a run of valves that had bad o-rings, guess who got one of them? Anyway, once we figured that out, the Andair folks quickly sent a new valve and problem solved.
Any hint of fuel smell in the cockpit means just that, there's fuel loose in the cockpit!
 
Gas Leak/Smell

I had a smell that I traced it to the fittings in front of the fuel totalizer between my fuel pump and fire wall. I tightened the fittings down and finally got rid of the gas smell forever.
It was worse when the fuel pump was on. Ah glad to be flying more and working on the plane less.

S S Anderson
 
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