Possible fuel leak question

billbogg · Post by **billbogg** » Sat Jun 12, 2004 2:18 am

I have a nice 52 B model with standard fuel tanks. I have been noticing for some time that when the tanks are topped and I fly through some turbulence that I smell gas fumes. It doesn't happen when the tanks are less than around 3/4 full. I've got an annual coming up in a few weeks and would like to solve my fuel leak mystery...any help from the membership would be appreciated. Thanks...............

blueldr · Post by **blueldr** » Sat Jun 12, 2004 2:50 am

The gas smell is probably coming from the cabin top vent on the cross cabin fuel tank vent line. This is a common occurrence on many C-170 airplanes. It may be a good idea to check that cross cabin line to be sure there are no leaks on the hose connectoins. The problem is most common when the tanks are full enough to occasionally flood that vent line. A steep nose down descent will also cause it. Later airplanes had the tanks vented out on the under wing behind the strut attach point.

blueldr · Post by **blueldr** » Sat Jun 12, 2004 3:08 am

In addition to the above comment:
The STC I used when installing the Continental IO-360 engine in my '52 B model did away with the cabin top vent and put two vents from the tanks out behind the strut attach points as on the later Cessna airplanes. I always used to get the gas smell in rough air when the tanks were relatively full and it was particularly severe on a steep nose down descent with a high fuel level. Moving the vents completely eliminated the problem.

Roesbery · Post by **Roesbery** » Sat Jun 12, 2004 6:18 pm

I just changed a fuel tank because it had a hair line crack caused by rubbing on the lip of the spar ( top forward, cabin end of spar) The used tank I put in had a rub mark in the same place but not as deep. Put fuel tank sealant on the spot and a rubber chafe strip between the tank and spar. Cause appeared to be the tank was not properly snugged down. The replacement tank did not touch at that spot after it was properly tightened down. No visable fuel leak was noted but a fuel smell was present when the tanks were full and during decent with full or nearly full tanks, upon removing the tank cover a fuel stain was on the top of the tank comming from the leak.