1969 182 fuel selector

islandboy

islandboy

Pre-takeoff checklist
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islandboy
Can anyone explain this?

The engine drew fuel only from the left tank, even when the selector valve was set to "Right". Switching the position of the selector felt normal.

A mechanic is looking into it, but I wondered whether anyone has a preliminary suggestion -- curious.
 
My guess is your fuel vent is plugged on the left tank.

sZOXT.png
 
Based on your picture, can you elaborate on the suspected paths taken (or not taken) by fuel from the left and right sources?

I'm just not seeing it.

gkainz said:
My guess is your fuel vent is plugged on the left tank.
Click to expand...
 
I'm pretty sure there are vents for both tanks and Greg means the right tank vent is plugged causing gas to siphon into the left. Of course that would only happen until the tank interconnect un-ported. I believe there are also check valves on the interconnect to keep liquids from shifting from tank to tank so a check would also have to fail.

Then again, maybe yer just flying without the ball centered...
 
I'd suspect pilot misinterpretation but I'd make darn sure the valve handle is clocked correctly.
 
This sounds a bit like what I experienced:

UNEVEN FUEL FEEDING

Have you been flying along and watched your fuel gauges show that your left tank is going down while the right tank remains full even with the fuel selector on "Both"? This is a common problem with Cessna 182 Skylanes before the 1979 model year. And the real shocker is that while the right tank is remaining full the engine is actually running off of fuel from the right tank!


What causes the situation is the way Cessna designed the fuel tank venting system. When fuel is used from a tank it must be replaced with something, otherwise a vacuum is created which will either cause interruption of fuel to the engine or cause the bottom of the bladder tank to be "sucked" up. To avoid this in almost all fuel systems, whether they are in an aircraft, a car or a lawnmower, fuel that is used from the tank is replaced by air from the outside.


In the Cessna 182 Skylane this venting occurs by connecting the upper outboard portion of the left tank to the "L" shaped vent tube underneath the wing behind the left wing strut. This allows air into the left fuel tank as fuel is used. To vent the right tank, a vent inter-connect line is run from the upper inboard area of the left tank to the upper inboard area of the right tank thus, in theory, venting the right tank to the vented airspace of the left tank.


Unfortunately, wing dihedral, where the wing tip is higher than the wing root, was not sufficiently considered. When the wing tanks are full, the vent interconnect line is actually submersed in fuel and thus as fuel is used from the left tank, the air coming in from the vent pushes fuel from the left tank through the vent interconnect line into the right tank, thus replacing fuel that is used from the right tank. And even after enough fuel is used from the left tank to bring the fuel level below the vent interconnect line the condition will continue as fuel sloshing in the tank periodically gets into the interconnect line and pushed through to the right tank.
In really severe cases fuel usage from the right tank might not be indicated on the gauge until the fuel level in the left tank is as low as 1/3 capacity. The positive thing to keep in mind when experiencing this condition is that fuel is actually being used from the right tank and that fuel being used from the right tank is merely being replaced by fuel from the left tank. This means that even if the left fuel tank should go to empty you will not experience fuel flow interruption as long as there is fuel in the right tank and the fuel selector is on "Both".


This condition can be minimized somewhat by adjusting the position of the fuel vent behind the lift strut on the left wing, making sure that fuel caps seal tightly so that the "head pressure" in one tank is not altered by a leaking cap, and assuring that the wing strut fairing is sealed against the strut, thus avoiding burbling air right in front of the vent. However, in the end the design of the system does not allow for complete resolution of the problem. The Cessna Pilots Association has a handout available to its members that discusses this situation in even greater detail.

Beginning with the 1979 model year the Cessna 182 Skylane went to an integral bay "wet wing" fuel system with vents under both wings which went a long way to reducing the problem.
 
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On the flight where the phenomenon may have started, I expected to be in the air for about 50 minutes. After climb-out, I ran from the left tank for 15 minutes and then the right for 15 minutes.

When I went to fly next, I was surprised to see that the left tank was about 10 gallons shy of the right, but I thought that I had perhaps made a management error. My next flight was expected to be about another 50 minutes, so I selected the right (fuller) tank for the whole flight except for the climb and descent, hoping to even out the tanks. After this flight, the left tank was down to around 5 gallons, and the right was still up at about 25 (the same as before the flight).

Stewartb said:
You stated you had selected a single tank, yes?
Click to expand...
 
Likewise ... I once accidently left the fuel cap off the right tank on my Sport Cub. In flight I noticed the right tank stayed full but the left tank was being depleted quickly. Turned out I was indeed losing fuel from the uncapped right tank, but the suction was causing fuel to crossfeed through the vent from the left over to the right, keeping it apparently full.

I was near Yakima, where the CubCrafters factory is located. I landed there, and did the first smart thing all day. I bought two replacement fuel caps.

:redface:
 
What's surprising me in particular is that I seem to be able to cross-feed from the left tank, even when there is a trivial amount of fuel in it. My reading of the basic left-to-right cross-feed issue is that the process should terminate as the level in the left tank drops below the expected level of the cross-vent (e.g., 1/2 tank).

Pilawt said:
Likewise ... I once accidently left the fuel cap off the right tank on my Sport Cub. In flight I noticed the right tank stayed full but the left tank was being depleted quickly. Turned out I was indeed losing fuel from the uncapped right tank, but the suction was causing fuel to crossfeed through the vent from the left over to the right, keeping it apparently full.

I was near Yakima, where the CubCrafters factory is located. I landed there, and did the first smart thing all day. I bought two replacement fuel caps.

:redface:
Click to expand...
 
islandboy said:
This sounds a bit like what I experienced:

UNEVEN FUEL FEEDING

Have you been flying along and watched your fuel gauges show that your left tank is going down while the right tank remains full even with the fuel selector on "Both"? This is a common problem with Cessna 182 Skylanes before the 1979 model year. And the real shocker is that while the right tank is remaining full the engine is actually running off of fuel from the right tank!


What causes the situation is the way Cessna designed the fuel tank venting system. When fuel is used from a tank it must be replaced with something, otherwise a vacuum is created which will either cause interruption of fuel to the engine or cause the bottom of the bladder tank to be "sucked" up. To avoid this in almost all fuel systems, whether they are in an aircraft, a car or a lawnmower, fuel that is used from the tank is replaced by air from the outside.


In the Cessna 182 Skylane this venting occurs by connecting the upper outboard portion of the left tank to the "L" shaped vent tube underneath the wing behind the left wing strut. This allows air into the left fuel tank as fuel is used. To vent the right tank, a vent inter-connect line is run from the upper inboard area of the left tank to the upper inboard area of the right tank thus, in theory, venting the right tank to the vented airspace of the left tank.


Unfortunately, wing dihedral, where the wing tip is higher than the wing root, was not sufficiently considered. When the wing tanks are full, the vent interconnect line is actually submersed in fuel and thus as fuel is used from the left tank, the air coming in from the vent pushes fuel from the left tank through the vent interconnect line into the right tank, thus replacing fuel that is used from the right tank. And even after enough fuel is used from the left tank to bring the fuel level below the vent interconnect line the condition will continue as fuel sloshing in the tank periodically gets into the interconnect line and pushed through to the right tank.
In really severe cases fuel usage from the right tank might not be indicated on the gauge until the fuel level in the left tank is as low as 1/3 capacity. The positive thing to keep in mind when experiencing this condition is that fuel is actually being used from the right tank and that fuel being used from the right tank is merely being replaced by fuel from the left tank. This means that even if the left fuel tank should go to empty you will not experience fuel flow interruption as long as there is fuel in the right tank and the fuel selector is on "Both".


This condition can be minimized somewhat by adjusting the position of the fuel vent behind the lift strut on the left wing, making sure that fuel caps seal tightly so that the "head pressure" in one tank is not altered by a leaking cap, and assuring that the wing strut fairing is sealed against the strut, thus avoiding burbling air right in front of the vent. However, in the end the design of the system does not allow for complete resolution of the problem. The Cessna Pilots Association has a handout available to its members that discusses this situation in even greater detail.

Beginning with the 1979 model year the Cessna 182 Skylane went to an integral bay "wet wing" fuel system with vents under both wings which went a long way to reducing the problem.
Click to expand...


This reads almost identically to the Cessna Pilot's Assn article.

Basically if you give John Frank a call, he can explain why it's an exercise in futility to not have fuel feeding from the opposite side in a 182 of almost any vintage.

The selector is damn near useless. Design change on top of design change trying to "fix" it only made it easier.

In later models there's four distinct fuel paths that can mix and match themselves to go around the fuel selector when the tanks are full.

When more than half empty, only two. Bank the airplane, fuel will flow across the vent lines in an uncoordinated turn.

The fuel selector valve can't even stop siphoning if you park with the wing vent equipped wing downhill. It'll just keep running.
 
islandboy said:
What's surprising me in particular is that I seem to be able to cross-feed from the left tank, even when there is a trivial amount of fuel in it. My reading of the basic left-to-right cross-feed issue is that the process should terminate as the level in the left tank drops below the expected level of the cross-vent (e.g., 1/2 tank).
Click to expand...


There's another path but I can't remember the mechanism right now. It's at home in my CPA 182 Systems manual and notes somewhere.
 
Yes, I found that much in the article bore suspicious similarities to my recent experience, so I thought a cut-and-past might shed some light on my situation.

Any relevant details that you might be able to share from your records would be appreciated.

denverpilot said:
This reads almost identically to the Cessna Pilot's Assn article.

Basically if you give John Frank a call, he can explain why it's an exercise in futility to not have fuel feeding from the opposite side in a 182 of almost any vintage.

The selector is damn near useless. Design change on top of design change trying to "fix" it only made it easier.

In later models there's four distinct fuel paths that can mix and match themselves to go around the fuel selector when the tanks are full.

When more than half empty, only two. Bank the airplane, fuel will flow across the vent lines in an uncoordinated turn.

The fuel selector valve can't even stop siphoning if you park with the wing vent equipped wing downhill. It'll just keep running.
Click to expand...
 
I also remember that there was an overfill on one of the sides. I think that it was the right side, but I can't be sure. Given the issues that I'm reading, I wonder whether some voodoo related to the overfill initiated the issue in my case.

So far, my mechanic hasn't found anything compelling. If no other clues come to light, I may give it a test run beginning with more modest fills of both tanks.

timwinters said:
Mine works fine! Like you say, they must have effed it up later.
Click to expand...
 
Start the engine and then turn the fuel selector off. Wait to see if the engine eventually quits. If it keeps running after three or four minutes, you have a bad fuel selector. They have O-rings in them for valve seats, and the valves themselves are steel balls that are actuated by a cam turned by the selector lever. Those O-rings get old and crack and crumble and will not shut the fuel off anymore.

That problem should be caught at annual when the mechanic checks the fuel strainer screen and bowl, but I have run into too many airplanes that have obviously not had their gascolators apart for a long, long time.

The Cessna fuel system will behave itself just fine if the fuel caps have decent gaskets (and the fuel filler flanges aren't all bent and corroded) and the silicone coolie-hat cap vent isn't shot. There will be some fuel transfer whe the tanks are full, or if the airplane is parked on a sideways slope with the selector on both. But it takes maintenance to keep stuff in decent shape.

Those silicone cap vents sag with age and lose their seal, and a pounding rain will splash water into the vent holes in the cap and it will drip through that vent into the tank.
 
Good suggestion (re: switching to off). Thanks for that and the other comments.

Dan Thomas said:
Start the engine and then turn the fuel selector off. Wait to see if the engine eventually quits. If it keeps running after three or four minutes, you have a bad fuel selector. They have O-rings in them for valve seats, and the valves themselves are steel balls that are actuated by a cam turned by the selector lever. Those O-rings get old and crack and crumble and will not shut the fuel off anymore.

That problem should be caught at annual when the mechanic checks the fuel strainer screen and bowl, but I have run into too many airplanes that have obviously not had their gascolators apart for a long, long time.

The Cessna fuel system will behave itself just fine if the fuel caps have decent gaskets (and the fuel filler flanges aren't all bent and corroded) and the silicone coolie-hat cap vent isn't shot. There will be some fuel transfer whe the tanks are full, or if the airplane is parked on a sideways slope with the selector on both. But it takes maintenance to keep stuff in decent shape.

Those silicone cap vents sag with age and lose their seal, and a pounding rain will splash water into the vent holes in the cap and it will drip through that vent into the tank.
Click to expand...
 
That's a good test. For clarity, I have the huge LR tanks (bladders) and the vent lines are far enough down you could easily lose 40 gallons overboard with the selector in the OFF position if the various components aren't set up right.

CPA has a complete document on the uneven flow problems (often caused by the left tank "ram" air vent not being positioned correctly almost behind the strut, and very common) and many of the causes of uneven in-flight flow are traceable to the same issues that make the fuel selector almost worthless with full tanks. Especially the big tanks.

The comment about the fuel cap air valve seals is a "big deal" on this problem because they're often overlooked or neglected and really easy and cheap to fix.

Mechanics hate working on those overhead vent lines, too. They're a PITA to get at. Whoever did the second set of bladders in ours didn't replace the little hose "jumpers" across the wing root gap and we had leaks eventually from them drying out and cracking. Our mechanic fixed them and cussed whoever didn't do it. LOL.

Was kinda an interesting way to terminate a flight. Practice area, doing some steep turns with a young pilot buddy and we see blue stuff running down the right side forward pillar. Hmm. Guess we will be heading back to the airport and the no smoking lamp is definitely lit. :) And of course at the time you're wondering, "Where the hell is THAT coming from?" And monitoring the fuel gauges a little closer than usual...

We've fiddled with the placement of our air vent a bit over time and have the uneven flow pretty much settled in. If full we will always draw more from the left tank (it's being pushed across the vent line by air pressure until the vent is no longer submerged) and then it evens out. Almost no amount of fiddling with the selector will make a hill of beans worth of difference. It'll slow the draw from the left to set it to Right, but can't really stop it until the fuel comes down a long way. Roughly half tanks. So you just kinda watch it do its thing until you've burnt off about three hours worth of fuel.

The LR tanks really aren't worth it on a 182 unless you have a need to tanker fuel somewhere that doesn't have any. They're just ridiculous. Kinda nice for a couple of back to back two hour flights though, like during training... still plenty on board in reserve after that.
 
islandboy said:
Based on your picture, can you elaborate on the suspected paths taken (or not taken) by fuel from the left and right sources?

I'm just not seeing it.
Click to expand...

What? We now have to THINK and ELABORATE on quick driveby quips? I keyed in on a half-mis-remembered memory about uneven fuel flow, found the diagram and popped it up without a whole lot of thought ...

At a glance, the thought was a plugged vent on the left tank, left tank selected, would cause fuel draw from the right tank thru the tank inter-connect pipe. But it's been years since I've flown a 172/182 so "I mis-remembered that I was in the BlackHawk that was being fired upon" ... :)
 
Understood...I appreciate your kind input.

gkainz said:
What? We now have to THINK and ELABORATE on quick driveby quips? I keyed in on a half-mis-remembered memory about uneven fuel flow, found the diagram and popped it up without a whole lot of thought ...

At a glance, the thought was a plugged vent on the left tank, left tank selected, would cause fuel draw from the right tank thru the tank inter-connect pipe. But it's been years since I've flown a 172/182 so "I mis-remembered that I was in the BlackHawk that was being fired upon" ... :)
Click to expand...
 
BTW - are you really in the Caribbean? Heading down your way in a few weeks ... Turks and Caicos, Samana, BonAire, Curacao, Aruba.

co-worker here grew up on Saint Vincent
 
Bon Tarde!

I used to spend a lot of time in Bonaire and Curacao, but those are off my list unless Venezuelan hyper-regulation of passing flights eases up.

I flew into St. Vincent about three weeks ago and have been in and out of the Grenadines, St. Lucia and Trinidad recently also.

The weather has been crap of late, so I'm waiting for the next break in the liquid sunshine. Hopefully, December will bring fairer skies, as I want to make some runs between the southern islands and Sint Maarten.

gkainz said:
BTW - are you really in the Caribbean? Heading down your way in a few weeks ... Turks and Caicos, Samana, BonAire, Curacao, Aruba.

co-worker here grew up on Saint Vincent
Click to expand...
 
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