Cessna 172M Fuel Smell Issue

[Famousghent]

I’m dealing with a bit of a funky situation with my Cessna 172M. I’m catching a whiff of fuel, especially when the tanks are topped off, but it seems to fade as the fuel level drops.

My mechanic took a look but couldn’t pin down the culprit. Has anyone else run into this? Got any ideas on what might be going on?

 

[Toga Cruiser]

Don’t want to sound like Kamala but fuel smells in side cabin are there because there probably is fuel leaking somewhere.
Check your primer , and your fuel sending units are located about where your ear is when sitting in pilots or copilots seat underneath the top cabin interior piece . The interior ceiling piece is not easy to remove but you can pull it back enough to see the sending units so you might look for them in the root fairings first. If they are leaking either replace or I have used JB weld and it works. Cessnas have several short rubber hose connectors above the headliner that get old and crack. There is a vent tube up there somewhere and a balance tube on some models.


Then there is the fuel selector valve about 6 inches under the fuel selector..
Also check fuel drains under each wing and engine compartment for leaks. Check your engine compartment for fuel tints around fuel lines and carb.
One last thing placing your fuel drain device back in cabin after draining tanks might be your problem.
I listed these things out of order so start with the easiest to do first.

 

[DNeuf]

Cessnas have several short rubber hose connectors above the headliner that get old and crack. There is a vent tube up there somewhere and a balance tube on some models.


Then there is the fuel selector valve about 6 inches under the fuel selector..

I've had both these issues over the years.
The hoses aren't too bad to replace.
With my fuel selector, the O rings could be replaced. There should be a plug button on the belly under the selector you can check for staining. Not a fun project to pull the selector.

 

[Mslisaj]

I had a similar issue with my R172k and it turned out the fuel selector had a slight leak at the shaft the handle connects too. Overhauled the selector and problem solved. Hope this helps.
Kind of easy to get in to the top of it through the inspection holes and see the valve.

 

[aerosputnik]

If the smell is there when the tanks are full to brimming, then the culprit is probably the gasket between the filler and the top panel. You'll have to unscrew the top panel and filler neck to remove the panel and change the gasket. Some earlier gaskets were made of cork and if the tanks are mostly left with less than half full, the the gasket dries out, cracks up and leaks into the wing void where the tank sits. From there the smell will come through the wing end rib and into the cabin behind the headliner.