Fuel Leak
 

OK here is a problem I haven't seen yet. Had a great trip to the Bahamas and back with no squawks except when I refuelled at KFLO, minor fuel stains developed over night on the under side of BOTH wing roots. The tank overflow drains were not dripping and the filler neck drains were clear. Underwing panels inboard of sumps were removed and nothing obvious found. Nil if any stains on the ground. The stains were cleaned off the fuselage and after landing at KSYR and having the acft sit over night, no fuel yet added, had no stains. However they began developing after the top off the next day. Minor fuel smell in cabin when you first opened it up. Fuel selectors were never changed from green/green (1979 P337H). My mechanic is going to have a look but appears a bit stumped at this point.
Has anyone had this ?

James, I had a similar leak but only on one wing, strange that it started doing it on both at the same time. My A&P had to remove the top panel above the fuel tank and replace the access plate gasket on top of the tank closest to the fuselage. Because of where your leak is I would guess its the inboard tank gaskets. In the parts manual look at figure 8 on page 104 Detail D #37. Cessna part #1516118-1. On the service manual look on page 330 figure 11-3 detail E. Hope this helps.

Brent

WE just had this problem on a customers P337H. The Three round caps on top of each inboard fuel tank were leaking out the gaskets. Wings have to be supported, fuel drained to about 15 to 20 gal, remove inboard tank access covers, change gaskets, and put it all back together. These tanks have fuel all the way to the top for quite a while, probably till 30 gals are burned out which is why when filled and flown you may not see leaks but sitting full overnight will show up. Also, the outboard tanks may need to be checked to if this doesn't totally resolve the problem.

You were right. Not sure why this happened to both sides at the same time.

Mine happened right after a week long trip to the Florida Keys, I wonder if the salt air ate the old gaskets up?

I suppose the salt air could have something to do with it.
I had my mechanic check the other tanks - photo attached for those curious to see what this looks like.
I will have him change all the cork strips that stop the tanks from chafing, also all the fuel lines because they have a life limit.

Hi James

When in the USA, McMasters is where I managed to obtain a roll of self adhesive cork strip, it comes in varied widths and lengths. It was also very reasonably priced. I replaced all the cork strips in both wings, top and bottom.

Just in case you can't find any.

Dave

Fuel tanks and bays - photos attached of what these look like for those who are interested.

Fuel Tank Leak
 

I to had the gasket leak on my 1978 337H a few years ago. The inboard take is under pressure when all tanks are full because the outer tanks are slightly above the inboard tank.
This little pressure will find any little leak in gasket and the fuel flows down and out next to fuselage. Dale Campbell

Inboard fuel tanks repaired (see image) and ready to install with new hoses.

Fuel leak
 

I just discovered I have a leak on my right tank on the inboard and trace it from top of the tank. I know its cork on the gasket, instead of cork can you use rubber? Thanks John

Gas leak
 

Yes the new gaskets are some kind of rubber I think they are neoprene