Cessna 182 Uneven Fuel Burn - Is It The Vent Or Is It....

Sinistar

Sinistar

En-Route
Joined
Sep 9, 2016
Messages
3,712
Display Name
Display name:
Brad
We just did our first family cross country on the old 182P. It was awesome getting to Grandpa's place in 1hr15min instead of 4.5hrs of driving and traffic :)

We did notice the trademark Cessna uneven fuel burn so I quickly attributed it to the fuel vent not be exactly, microscopically perfectly aligned behind the strut. But my wife (PIC, left seat) said we weren't level as I was flying. So am I too quick to blame the fuel vent? If newbie me had just flown level would we have had even fuel burn? Can I use the excuse that its hard to read the AI from the right side :)

This was our first trip where we had baggage, about 110lbs including the spare oil, jumper cables, etc. I am about 60lbs more than my wife and 9yo daughter combined. Plus I had loaded the heaviest stuff on my side (duh!). So it was probably 90lbs more on the right than the left.

So maybe the vent isn't the issue - was the uneven fuel burn just from my wing being low so it burned mostly from their side? Or is the vent supposed to counteract this uneven wing level?

On the way back I placed the baggage differently and the unevenness was less so but we also had a tailwind and took about 15 minutes less.

And we have a wing leveler...should that be used just to address this uneven fuel use?
 
You could drive yourself nuts trying to track this down. Check the service manual to see if your vent tube is in the correct position (not uncommon to be incorrect). Next, check your fuel caps to see if there might be an issue there (fairly rare). Unless it is so unbalanced that you're seeing difference of ~15-20+ gallon or more burn difference per side, routinely, I wouldn't worry about it. Also, do be sure to set the fuel selector to one side or another when you're fueling, otherwise you may be cross-feeding while fueling, which can result in some imbalance, depending on ramp slope while fueling.
 
Sinistar said:
If newbie me had just flown level would we have had even fuel burn?
Click to expand...
It's possible.

A couple things to consider...As we know, Cessna singles use a gravity fed fuel delivery system. Sometimes you may find that fuel from the left tank is used faster than fuel from the right, because the fuel vent is located in the left wing (as you mentioned.) The only other thing I can think of right now that would likely cause an uneven fuel burn, besides non-level flight, would be a restriction in the fuel outlet, or a leaking fuel cap. If a cap is leaking, than excess airflow is moving through the crossvent and the result is different pressures in each tank.

Curious to know.., how much fuel did you begin with in each tank and what did you end up with upon landing?
 
I'm not 182 guy, but flying my skywagon and lots of 200 series, doesn't your POH says to switch between tanks during cruise and not just leave it on both??
 
The 182 POH (Q model, at least), contains no such language, other than uncoordinated flight can result in unbalance fuel burn. It clearly says operation on one tank only is for level flight only, and that BOTH needs to be used for takeoff and landing.
 
The Skylane service manual should have service instructions for aligning your underwing vents and also for how to check your vent lines. Vent positioning tolerance is +/- .03" from specification.

See pages 12-10 and 12-11 here. It's exactly the same as in my Skywagon manual. Or find the appropriate service manual if this one doesn't apply to your model. http://www.redskyventures.org/doc/c...s/Cessna_182&Skylane_1969-1976_D2006-4-13.pdf
 
Last edited:
Owned a Lane for years and hung around with other Lane owners. Yeah, vent tube position, caps (leaking gaskets), mud daubers in the vent (mine), and flying around on both, are all likely suspects. The lines from the fuel pump to each side are not the same total length and along with minute differences in air pressure across the wing span can result in differential fuel level.
 
My 182Q has a big disparity between tanks it uses. It really doesn't touch the right tank until the left one is over half empty. It's really weird. For longer x-country flights I usually try to switch to the right tank for a hour or so just to keep the weights somewhat even but even if I don't eventually it pulls from the right.

It was concerning at first to me but it really presents no safety hazard as it does pull from both, albeit very unevenly.
 
Even selecting the right tank, my 182P guages will indicate a draw from the left tank (vented) until about 1/2 - 3/4 and then I will notice the guage decreasing on the right side.

For a reference, this is verbatim from the 182P Owner's Manual fuel system section (without the diagram).


"FUEL SYSTEM.

Fuel is supplied to the engine from two tanks, one in each wing. With

the fuel selector valve on BOTH, the total usable fuel for all flight conoutlet,

ditions is 60 gallons for the standard tanks.

Fuel from each wing tank flows by gravity to a selector valve. Depletely

pending upon the setting of the selector valve, fuel from the left, right,

or both tanks flows through a fuel strainer and carburetor to the engine

induction system.

The fuel selector valve should be in the BOTH position for take-off,

climb, landing, and maneuvers that involve prolonged slips or skids.

Operation from either LEFT or RIGHT tank is reserved for cruising

flight.

NOTE When the fuel selector valve handle is in the BOTH

position in cruising flight, unequal fuel flow from each

tank may occur if the wings are not maintained exactly

level. Resulting wing heaviness can be alleviated

gradually by turning the selector valve handle to the

tank in the "heavy" wing.

NOTE

It is not practical to measure the time required to confeet,

sume all of the fuel in one tank, and, after switching to

the opposite tank, expect an equal duration from the remaining fuel. The airspace in both fuel tanks is interconnected

by a vent line (see figure 2-2) and, therefore,

some sloshing of fuel between tanks can be expected

when the tanks are nearly full and the wings are not level.

For fuel system servicing information, refer to Servicing Require tive

ments on the inside back cover"
 
Uneven fuel burn is a common know issue in the 182. On my regular XC trips I am right take 70% of the time then back to both when tanks even out...don't think I ever fly on left tank.
 
The Cessna Pilot's Association has a little two page article on why this is and what to do about it. Yes, it is venting. The answer if it bothers you, you can adjust it, but it really isn't a big deal, it evens itself out after the tanks drain down a bit.
 
So we log every flight in a notebook that we keep with the plane. Basically just the tach times, oil levels and tanks levels. I usually update a google spreadsheet and finally had time to enter all the more recent flights today. Here is what I am seeing:

Out of about 65 flights I threw out all the short flights of 20 minutes or less.
All of this data is with the tank selector always set to both.
LeftSeat(My Wife) : Right Seat (Open) ==> 1.5x gals more from open seat side
LeftSeat(My Wife) : Right Seat (Me) ==> 2.8x gals more from her side (she is obviously lighter)
LeftSeat(Me) : Right Seat (CFI) ==> 2.0x gals more from CFI's side (he is considerably lighter)

So the problem isn't always on just one side. And the amount of the difference seems to track with the weight difference. I did mention the tank vent to our A&P when we dropped it off for the Annual and he said it was correct. We have the later caps and once again the problem seems to shift sides. One thing that probably complicates matters is if we do 2 or 3 flights without filling up then one tank starts to have less than the other making the lighter side even lighter. So we definitely need to be using the fuel selector during these longer flights. Also, the tank level indicators are probably off with the wing tilt so its even more complicated! Oh yeah, and I now have proof that I am too fat :)
 
Cessna (most single engine models) are notorious for uneven fuel burn. Best to not obsess about it and learn to live with it.
 
All high-wing gravity fed aircraft seem to have this "problem". Of course, there is a tiny chance of obstruction or kink, but the culprit is probably un-coordinated flying. In our older CT aircraft, we have only "on" or "off", so we monitor the levels and fly with the ball maybe 1/2 out, one way or the other. The result is one wing being higher, and the feed will generally favor the higher wing. BTW, more than one owner has discovered their ball was not calibrated properly, by noticing consistent uneven fuel flow.
Plugged vents have also been known to interfere with fuel feed.
 
Just so I can sort this out in my head....

Are two people posting under your user name? I thought I just read something about your first solo.

Another possibility is im all sorts of screwed up due to holiday imbibing.
 
Kritchlow said:
Just so I can sort this out in my head....

Are two people posting under your user name? I thought I just read something about your first solo.

Another possibility is im all sorts of screwed up due to holiday imbibing.
Click to expand...
Nope, just me posting.

My wife is already a pilot so she was PIC for our family trip. And yes, I did just solo last week. One thing I thought was odd about our trip was the uneven fuel burn seemed to switch sides compared to all my training flights where I've been in the left seat and my cfi in the other seat. Didn't mean to confuse anyone and this flight was definitely not a training or solo flight. Although I learned a lot about navigation and vors on this flight as she knew I will be starting dual cross countries with my cfi as early as next week
 
Tell your wife she's fulla sh$t. It ain't your flying. It's the venting. You can be nicer than that if you like. :D
 
JCranford said:
Tell your wife she's fulla sh$t. It ain't your flying. It's the venting. You can be nicer than that if you like. :D
Click to expand...
She just laughed, heard much worse when she was flying for a living!
 
Stewartb said:
The Skylane service manual should have service instructions for aligning your underwing vents and also for how to check your vent lines. Vent positioning tolerance is +/- .03" from specification.

See pages 12-10 and 12-11 here. It's exactly the same as in my Skywagon manual. Or find the appropriate service manual if this one doesn't apply to your model. http://www.redskyventures.org/doc/c...s/Cessna_182&Skylane_1969-1976_D2006-4-13.pdf
Click to expand...

Where's the best place to buy a hard copy of that manual?
 
Okay, one other symptom. One evening doing a long pattern work session we started with 35 gallons in the left tank and 15 in the right tank. So it was already imbalanced from the session the night before. After the flight the the right tank was dry. The selector was on both the entire time. Shouldn't it have drawn at least something from the left tank? Both measurements were taken parked in the hangar in the same parking position. Needless to say I filled it up again as I didn't want the bladder totally empty.

We're probably fighting one other battle. The tanks never even out overnight in the hangar so right wing must be sitting higher up...or its just another venting oddity.
 
16 years flying a 182RG... It ain't worth chasing. If it gets too out of balance, just switch to the fuller tank for a while.
 
Yes, uncoordinated flying or bad rigging can exasperated uneven fuel burning . . . .

but

it can (and in Cessna, will) happen in a perfectly rigged plane flown straight and level with perfect coordination.
 
Sinistar said:
Okay, one other symptom. One evening doing a long pattern work session we started with 35 gallons in the left tank and 15 in the right tank. So it was already imbalanced from the session the night before. After the flight the the right tank was dry. The selector was on both the entire time. Shouldn't it have drawn at least something from the left tank? Both measurements were taken parked in the hangar in the same parking position. Needless to say I filled it up again as I didn't want the bladder totally empty.

We're probably fighting one other battle. The tanks never even out overnight in the hangar so right wing must be sitting higher up...or its just another venting oddity.
Click to expand...

Yea, as others have said- I think you are fighting a losing battle trying to figure it out. As long it is pulling from a tank, even if it runs one dry first, there is really no risk. Just pull from one tank or the other on long flights so the weight doesn't get too out of whack and you should be fine.
 
Oftentimes when I hear about/ observe a customer experiencing uneven flow it is due to not being coordinated in the climb and cruise (which would make sense if your wife said you weren't flying level). If the rudder trim on the 182 (or footwork on the pedals) isn't set keeping that ball in the center, one wing will be higher than the other causing an uneven fuel draw. If that isn't the case then it could be issues mentioned above by the others.
 
Sinistar said:
Okay, one other symptom. One evening doing a long pattern work session we started with 35 gallons in the left tank and 15 in the right tank. So it was already imbalanced from the session the night before. After the flight the the right tank was dry. The selector was on both the entire time. Shouldn't it have drawn at least something from the left tank? Both measurements were taken parked in the hangar in the same parking position. Needless to say I filled it up again as I didn't want the bladder totally empty.

We're probably fighting one other battle. The tanks never even out overnight in the hangar so right wing must be sitting higher up...or its just another venting oddity.
Click to expand...

If your fuel selector is on both the tanks should seek level. It doesn't take very long for it to happen and in fact should happen in flight, too. My parking in town is a little low on the right wing so I usually have 10+ gallons more in the right wing at start up. At my cabin the left wing is low so the same thing happens to the other side. In flight the levels equalize fairly quickly regardless which wing started with more fuel. That's how it's supposed to work.
 
Cessna Pilot's Assn has a tech guide on the problem that references the service manual and has all of the fixes.

You can do every one of them, and an old 182 will still burn unevenly. LOL.
 
denverpilot said:
Cessna Pilot's Assn has a tech guide on the problem that references the service manual and has all of the fixes.

You can do every one of them, and an old 182 will still burn unevenly. LOL.
Click to expand...
That's what I was going to ask. I've owned a 182P now for 2 years, the vent tube is not per the drawing. Just wondering if anyone else corrected theirs and then saw improvement.
 
Just crush that 182 and buy a 1971 Cardinal RG. Besides getting a wider cabin, you get the on/off fuel selector from the C-150.

So when you get uneven fuel flow you can either go nuts with the rudder to try and clear the vent (and then have to clean up passenger puke), or do what the cool kids do and just live with. The fuel will sort itself out sooner or later.
 
I logged about 20 hours late this summer in a 2011 182T G1000 model over 7 cross country flights. This near new (by my standards) airplane did exactly the same thing. In cruise, with the fuel on "both", autopilot engaged, it would sometimes be pretty even, other times draw from one side preferentially creating significant differential - and not always from the same side either.

It's like a software bug Microsoft can't fix...it stops being a bug and becomes a feature. :cool:
 
Sinistar said:
We just did our first family cross country on the old 182P. It was awesome getting to Grandpa's place in 1hr15min instead of 4.5hrs of driving and traffic :)

We did notice the trademark Cessna uneven fuel burn so I quickly attributed it to the fuel vent not be exactly, microscopically perfectly aligned behind the strut. But my wife (PIC, left seat) said we weren't level as I was flying. So am I too quick to blame the fuel vent? If newbie me had just flown level would we have had even fuel burn? Can I use the excuse that its hard to read the AI from the right side :)

This was our first trip where we had baggage, about 110lbs including the spare oil, jumper cables, etc. I am about 60lbs more than my wife and 9yo daughter combined. Plus I had loaded the heaviest stuff on my side (duh!). So it was probably 90lbs more on the right than the left.

So maybe the vent isn't the issue - was the uneven fuel burn just from my wing being low so it burned mostly from their side? Or is the vent supposed to counteract this uneven wing level?

On the way back I placed the baggage differently and the unevenness was less so but we also had a tailwind and took about 15 minutes less.

And we have a wing leveler...should that be used just to address this uneven fuel use?
Click to expand...
She said you weren't level but you didn't seem to notice that. Was the ball centered? Were you having to work a lot to hold a heading? We're the 'wings' in the AI level?
 
Mark Ebben said:
That's what I was going to ask. I've owned a 182P now for 2 years, the vent tube is not per the drawing. Just wondering if anyone else corrected theirs and then saw improvement.
Click to expand...

We messed with ours for a couple of years. Not a lot, but we did move it around. Sometimes it helped, other times you would load up the airplane different and it’d burn unevenly again.

Definitely not worth losing any sleep over though. We don’t have to set timers and switch tanks all the time like the Piper/Grumman/Mooney/whatever folk. :)
 
JimNtexas said:
Just crush that 182 and buy a 1971 Cardinal RG. Besides getting a wider cabin, you get the on/off fuel selector from the C-150.
Click to expand...

Ruh roh, careful, you're gonna get accused of fake news by the 182 koolaid crowd with that kind of baiting.:D Apparently they use nautical inches....:rolleyes:
 
denverpilot said:
We messed with ours for a couple of years. Not a lot, but we did move it around. Sometimes it helped, other times you would load up the airplane different and it’d burn unevenly again.

Definitely not worth losing any sleep over though. We don’t have to set timers and switch tanks all the time like the Piper/Grumman/Mooney/whatever folk. :)
Click to expand...
Thanks, right now I just switch to the right and set the timer, then back to both.
 
luvflyin said:
She said you weren't level but you didn't seem to notice that. Was the ball centered? Were you having to work a lot to hold a heading? We're the 'wings' in the AI level?
Click to expand...
it's been awhile since this flight so details are getting sketchy. She was PIC in the left seat. I was just getting in some flight control time in the right seat. And unlike all these crazy instructors, I find it really hard to see the AI and turn coordinator from the right seat. Plus I hadn't done a lot of cross countries myself to learn about these long periods of flight with a wing low. In other words I wouldn't have noticed if she hadn't said something. Now I'm much more aware of it. But I get to blame her since she was PIC :) Hell, maybe she needs a little spanking for that tomorrow night!
 
Assuming 48" between the inboard sides of the tanks in a 182, a 2 degree bank due to sloppy flying will create a 1.67" difference in height between the two outlets. 2.5" for a three-degree slip. The tank is only about six inches deep, so any difference in height makes a difference in head pressure, and the high tank will flow a lot faster, sometimes faster than the engine is using the fuel. Just try parking the airplane on a slight sideways slope, with the selector on Both, and see what the fuel does.

The fuel in the vertical lines is all part of the head pressure. If one tank runs dry due to really sloppy flying, it can go only so low in that tank's line before the head pressure of the other stops it. Unless, of course, there's some restriction in the line somewhere, upsetting the flows.

Attitude indicators and turn coordinators are mounted in the panel with slotted holes to permit the mechanic to level the instruments with respect to the airframe. Sometimes that care isn't taken and the pilot wonders why the airplane flies funny.
 
You must log in or register to reply here.
Back
Top