Fuel smell

[nmflyr]

When I am flying and getting tossed around, I can smell a faint odor of fuel. I have not been able to find any staining or seeping. I have looked under the wing root cover and not found any staining. I replaced the vent lines and hoses with no difference. I thought it might be coming from the fuel gauge gasket, but there is no sign of fuel in that area.

Does anyone have any experiences with this issue?

[Robert Eilers]

Check the area behind the fuel vent, above the cabin. Som 170s, including mine, will spit fuel out of the overhead vent in turbulence, when the tank is full or nearly so. If so, there should be some tell-tail streaking behind the overhead fuel vent.

[GAHorn]

The most common area for this sort of thing is the fuel selector valve (top/cover o-ring), the fuel-vent crossover tubes/hoses, the gooseneck vent, and fuel cap area.
If you've already examined your vent tubes/hoses and no signs of fuel staining... or it occurs even with lower-than-full tanks....then look beneath your flap-handle tunnel at the fuel selector valve.

If your fuel tanks are very full...you might spit a bit out the cap area... or if you land and slow down rapidly your gooseneck vent might vomit a bit out the cabin roof.

Very rarely... a carburetor float set too high can overflow the carb bowl in flight. Look for excessive staining. (You ARE using AVGAS aren't you?... Mogas may not leave evident stains.)

Other, less common locations, at inside the doorposts where the lines descend.

[jlwild]

One further remote place to look for leaks is from the fuel tank. The reason I mention it is I discovered two locations on my right fuel tank that were beginning to seep. One was the weld around the male flange where the fuel line connects to the gas tank and feeds down through the cabin area. The second was from the four, over length, screws holding the right door stop (Fig. 3-109 170B IPC) to the channel (Fig. 3-108 170B IPC) under the fuel tank. The four screws dempled the center forward bottom part of the tank and were beginning to seep.

A third place to inspect is the fuel line union (Fig.63-10 170B IPC) hidden in the channel above and forward of the rear door post and behind the headliner. The line had shifted on mine sometime before I bought it and union, and gas line, were rubbing on the channel edge. When replacing the headlinner, the stain was noticable on the line and channel but not the old headliner.

First check all the other more common sources, discussed above, for leaking before removing headliners and fuel tanks.

[hilltop170]

Some of the fuel vent goose-necks on top of the cabin have a small hole drilled on the back side as an emergency vent in case the front port gets iced over. These holes can siphon gas, especially when the tanks are full and you fly in some turbulence.

[blueldr]

When I had the same problem, I finally found it in the two fuel hoses that connect the cross cabin vent line to the tee on the bottom of the gooseneck, which is up behind the headliner and easy to forget about. They were what appeared to be old original hoses that were all cracked and were connected with the old original type hose clamps.
I had been looking for the source of the gas smell for many weeks, and finally found it when I had relatively full tanks and dumped the nose to go down into the canyon going into Johnson Creek, Idaho. When the tanks are relatively full and you dump the nose, that vent line floods and I found it when the gas dripped on my throttle hand. The gray wool headliner was soaked and dripping gas. Just what I had always wanted up there where there wasn't a prayer of a place to get down alive until I got to the JC airport. Thank god I had a really strong pucker string 'cause that sure as hell tested it.

[paulbritton88]

Mine spits fuel out of the vent when doing stalls or in turbulence with full tanks. When it does, I smell it.

[Roesbery]

Two more possibles that I have seen are: water freezing in the overhead vent lines and splitting the tubing, more likely in snow country. and the fuel tank rubbing on the lip of the main wing spar causing a hairline crack which would seep when the tank was full.

[blakelewis]

Blueldr,
The parts out of the IPC:
Hose (vent to line) s-51-6-9
Hose (vent line to tank right) s-51-6-8
Hose (vent line to tank left) s-51-6-12
Clamp NAS397-12 (tinnerman A3122a-12-59)

Do you know what kind/size of hose to use? I am not finding the part numbers above on line.
I have seen that style of clamp but not that size. My current clamps in the right wing root are worm drive.

When I had the same problem, I finally found it in the two fuel hoses that connect the cross cabin vent line to the tee on the bottom of the gooseneck, which is up behind the headliner and easy to forget about. They were what appeared to be old original hoses that were all cracked and were connected with the old original type hose clamps.
I had been looking for the source of the gas smell for many weeks, and finally found it when I had relatively full tanks and dumped the nose to go down into the canyon going into Johnson Creek, Idaho. When the tanks are relatively full and you dump the nose, that vent line floods and I found it when the gas dripped on my throttle hand. The gray wool headliner was soaked and dripping gas. Just what I had always wanted up there where there wasn't a prayer of a place to get down alive until I got to the JC airport. Thank god I had a really strong pucker string 'cause that sure as hell tested it.

[fishdoc]

Mine developed an occasional slight leak on the primer 'o' ring.
Not enough to drip but enough to create gasoline smell in the cockpit.

[Bruce Fenstermacher]

Blueldr,
The parts out of the IPC:
Hose (vent to line) s-51-6-9
Hose (vent line to tank right) s-51-6-8
Hose (vent line to tank left) s-51-6-12
Clamp NAS397-12 (tinnerman A3122a-12-59)

Do you know what kind/size of hose to use? I am not finding the part numbers above on line.
I have seen that style of clamp but not that size. My current clamps in the right wing root are worm drive.

Blake, you won't find those part numbers. It is common fuel line hose. BL and I would probably use NAPAs best fuel line and worm drive clamps.

[blueldr]

blakelewis,

As bruce mentioned above I simply made the necessary repair with common 3/8" fuel hose and worm clamps. The hoses on the bottom of the goose neck vent are hidden and it's one of those "Out of sight, out of mind" things, I guess. I knew there were hoses up there but I just never remembered them until they leaked.

[GAHorn]

Blueldr,
The parts out of the IPC:
Hose (vent to line) s-51-6-9
Hose (vent line to tank right) s-51-6-8
Hose (vent line to tank left) s-51-6-12
Clamp NAS397-12 (tinnerman A3122a-12-59)

Do you know what kind/size of hose to use? I am not finding the part numbers above on line.
I have seen that style of clamp but not that size. My current clamps in the right wing root are worm drive.

Blake, you won't find those part numbers. It is common fuel line hose. BL and I would probably use NAPAs best fuel line and worm drive clamps.

Cessna used the nomenclature developed in-house for thsoe part nos: S-51 refers to a dwg number, and the "-6" refers to AN size 3/8" hose. the second dash-numbers (-8,-9,-12) refers to specific locations. So the answer is for you to obtain some aviation Aeroquip 306 or Stratoflex 193 hose (either of which meet Mil-H-5593 for low-pressure oil/fuel/air)in "dash 6" size (3/8") and cut it to length. Cost is about $5/ft. Install with aviation grade hose clamps....I like the Aero-Seal but Breeze is also good (both are worm-drive) all of which is available from Aircraft Spruce. 877-477-7823 or www.aircraftspruce.com

[blueldr]

Blake,
George has it pretty well lined out for you. However. you can bet your sweet patootie that I never bought any $5/ft., 3/8" fuel hose. I got it at Pep Boys Auto Supply, just don't tell 'em it's for an airplane.

[bagarre]

The Pep Boys line must hold up to ethanol better than that Aeroquip stuf