The International Cessna^® 170 Association

I need some input from the fuel tank guru's.

I am starting to see some fuel leaks on the right wing at the trailing edge inboard wing. I am attaching pictures. I know it could be anywhere, but do ya'll have any recommendations of any common areas of leakage to be looking at first before I tear into the fabric?

Secondly, if we do have to go into the fabric, what is the preferred way to mitigate the fabric replacement/damage?

What would be the recommended steps to get into it? Headliner out first?

I’d suggest looking to the Cessna 120-140 Association for suggestions. Here’s one thread on their website on this subject.

Because the leak is in your right wing—with its two tanks—rather than the left wing, the odds are at least twice as likely that the leak is at a fitting. I’d start by removing the wing root fairings to check for leaks at the finger strainer.

Hoping that the leak is from a deteriorating hose rather than a crack in the tank, I would next try to inspect the two tank interconnect hoses and interconnect vent line in the least obtrusive way possible. A small hole (3/8”?) in the top or bottom skin strategically placed between the tanks would allow for borescope inspection. Use a soldering iron to burn a hole in the fabric only if you can be sure that this won’t light the plane on fire.

I assume that the fuel dye will easily identify the source of the leak but there are other ways of finding leaks. Google “smoke leak detection” and “ultrasonic leak detection”. Be careful not to over-pressurize the tank if you use any of these other methods.

Section 4 of AC43.13-1B covers fabric repairs but the primary source for restoring the fabric once you get the leak fixed should be documentation from the company which provided the STC for your 170 — i.e. Ceconite, Poly-Fiber, etc.

Just an additional wag, check the fuel gauge base to see if the gasket is weeping.

If it's not the fuel gage or the outlet fitting, it's hard to believe that you could do any fix without pulling the tank(s).
I do not believe that the tank interconnect tubes can be replaced without pulling a tank. 
I have seen Ragwing tanks which were corroded at the contact with the felt pads on the tank supports.
Hopefully it's the fuel gage or an outlet line, which should be inspectable by opening the wing root fairings.

What do you see behind the inspection cover?

n2582d wrote: ↑Tue Feb 11, 2025 2:39 pm What do you see behind the inspection cover?

Yep…THAT is the question! Also, that sump-drain may look dry….but it’s so close to the fuel stain as to be suspicious. How much fuel actually drips? Have you placed a bucket beneath it to measure it..? or is the stain the only indicator? (i.e., is this perhaps only a one-time event?)

Hi Jim,

Where do you suggest to get a replacement gasket?

c170b53 wrote: ↑Tue Feb 11, 2025 1:35 am Just an additional wag, check the fuel gauge base to see if the gasket is weeping.

I'm awaiting a camera and bore scope. Hopefully the come tomorrow with the gear.

n2582d wrote: ↑Tue Feb 11, 2025 2:39 pm What do you see behind the inspection cover?

It is just stain indications under the wing. The pictures are posted above. I do not see any fuel on the ground.
We hope to open it up this week.

GAHorn wrote: ↑Tue Feb 11, 2025 4:13 pm

n2582d wrote: ↑Tue Feb 11, 2025 2:39 pm What do you see behind the inspection cover?

Yep…THAT is the question! Also, that sump-drain may look dry….but it’s so close to the fuel stain as to be suspicious. How much fuel actually drips? Have you placed a bucket beneath it to measure it..? or is the stain the only indicator? (i.e., is this perhaps only a one-time event?)