Fuel Smell in Cabin

[Mooney_Allegro]

I've noticed that when I topoff the tanks after a flight, let the plane sit in the hangar for about a week, when I come back & open up the cabin door, I smell a strong fuel odor.  It's only when the tanks are full though.  My last annual was last August, and the mechanic took the side walls out and said there were no leaks at that time.  I don't see any fuel leaks ontop or underneath the wings.  Is this normal for a Mooney to have the fuel smell when you open the cabin door when the tanks are full after sitting for a week?  Any ideas?  Thanks.

[KSMooniac]

The fuel smell can come into the cabin from the leading edge cavity of the wing...you could have a leak near the upper portion of the spar that vents into the cavity (and the cabin) without leaving an easily visible stain.  You also might notice the odor in flight once you put your gear down too.

[airguy55]

I have found that the fuel sending unit gasket is a huge creator of in cabin fuel smells, once again no real blue stains  on the gasket but fill the plane up, remove side panels and spray dye penetrant developer around the sending unit.  This is how I found the leak, it will slowly turn light blue.

change gaskets and new rubber washers under screws   walla.

[Mooney_Allegro]

Thanks guys for all the good info.  I didn't know there was a fuel sending unit behind the side wall.  I guess it's on the vertical portion below the pilot side window?  What about on the right side? Right below the door?  I don't notice any odor when I lower the gear or when I'm flying, only when I open the cabin door after about a week when the tanks are full.

[airguy55]

Yes below the door panel right foward of the rear seats. and same position oppisite side.  I have also seen the fuel selector oring leak and make a smell, but 95% of the time its the sending units.

 

You can also use baby powder and blow it onto the area to see if it is leaking.  It will get a blue tint.

B

[r0ckst4r]

Sorry to bring this back from the dead.   Basically have this problem now.   Anyone have any more information about this like part numbers for those fuel sender gaskets.  Is this a private pilot job or mechanics only?

[FlyingScot]

I had this problem - my O2 in annual we pulled the panels on both sides and found very slight weeping leaks around the tank gasket on both sides - the ones on the wing tank bulkheads low on the wall about as far back as the end of the front seat rails (see fig #40). The gaskets are penetrated by the fuel line from the tank and are affixed with two screws, also through the gasket - and a couple of these were weeping as well. My fuel sender gasket was replaced last year (leaking too). That is a more involved repair than this one (harder to get to)  

A&P Job, definitely -  and a pain since I had full tanks ;-) Hope this helps.

Cheers - Bob

 

[carusoam]

Great details, Bob!

Of all the possible fuel leaks... this is probably the easiest to fix.

Often old gaskets would lose their compressibility...

Sometimes the screws don’t get torqued evenly...

or Proper sealant isn’t available...
 

 

But, As usual... we can add to your list of things to consider...

Do you have the original senders in there?  Or has there been a Cies upgrade?

If getting the work done now... it may make sense to add the digital sensors to the order...  (higher accuracy, better detail)

 

PP thoughts only, not a mechanic...

Best regards,

-a-