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185 Uneven fuel usage from tanks

Tom3holer

Tom3holer

MEMBER
Cape Cod
I have a 73 185 with the small tanks, which is new to me, and have noticed that the fuel usage is much greater from the right tank than the left. It is confirmed by sticking the tanks.
The plane flys wing level. The other day I flew and at one point, fuel selector on both, the right tank indicated empty and the left was over half full. Sticked it shortly after landing and indeed that was the case. I had thought I had read about the tank vent tubes had to be positioned properly for equal fuel usage but in reading the service manual they only mention it as to reduce icing.

Learned the hard way if you top off the mains don't park it other than on the level and if you can't do that then select one tank or the other to prevent cross feeding to the downhill tank.

Tom
 
you could be slightly in a skid to favor fuel feeding from the right.

before you go there, the ball could be off; it only takes a tiny bit to use fuel from one side more
 
As Stewart says, start with the position of the vents. It may take a bit of testing to get it solved. This is not uncommon, btw.

MTV
 
I'm with Tango. Any uneven ball makes a difference in feed in my Cessna experience. If you're just cruising, it's easy to burn off the heavy tank to balance. If you need a reminder, put a potato chip bag clip or another visual clue on the yoke to remind you of burning off one side. I think ball matters more than wings level you mentioned... good luck
 
Gravity works even when in flight. If the fuel selector is on both and you fly with one wing high the tanks will cross feed as gravity seeks to level the fuel. One would assume anyone with a 185 probably has an AH gyro and knows what wings level looks like.
 
Is there any evidence of fuel stains on top of the wing behind the filler cap? This would indicate a tired cap "O" ring or loose cap which could be placing a suction on that tank causing the engine to draw more on the other tank.
 
Thanks everyone,

The ball was centered, nice to have rudder trim, and the wings were level as I was making sure so as to try and diagnose the problem.
Visually the vent tubes look the same but will measure them tomorrow.
The clip is a good Idea, thanks. There are no signs of fuel stains on the top of the wing.
In looking at the fuel schematic it appeared that if the fuel selector was on one tank or the other fuel would not crossfeed on the ground if on a slight slant as It does when on both. Guess I was wrong, as it did over the last two days with just the left selected.
I swapped fuel caps today and will be flying tomorrow and see if that makes any difference.
 
Just because the ball in the panel says you are level/coordinated, does not mean the plane is.

If the instrument is off just slightly in the mounting, it will be flying in a skid. To test you need to level the plane and then check the ball attitude.

In reality, this is NOT a big deal. Switch to one tank and fly on long trips, back to both for landing.

Pipers require tanks to be switched often.
 
With LONG hard climbs my 180K will draw significantly more from the right side but as you get lower (say bottom 1/3) it gets pretty even, I can reduce it by keeping the ball perfect but it is still asemetric. Short climb and quick level out and virtually the same useage L/R.
 
I've never seen a Cessna in my life that would feed evenly from both tanks when set on "both" on the fuel selector. Every airplane seems to have some venting issue or something that makes one tank feed more than the other. It's just a fact of live.

On my 180 I would only have the fuel selector on "both" on takeoff. Otherwise I would specifically select one tank or the other for X amount of time to manage my fuel load. That way I would always be sure of what was in each tank.

also, as some others have mentioned, make sure you put the fuel selector on either "left" or "right" during refueling in order to make sure you get the airplane completely full (or to make sure you know exactly how much is in each tank). If you have the fuel selector on either "both" or "off", the tanks can cross-feed during refueling and you will not be able to guarantee that a particular tank has the quantity of fuel in it that you thought it did.
 
Going to fly tomorrow and will fill both tanks. The fuel pad is level so will check the ball for center; checked tire pressure today and it was equal.
 
So how far from equal do they get? At Lake Hood my plane parks slightly right wing low. My right tank will always have 10 gallons more than the left. At the cabin the opposite is true and to a greater degree, like 15 gallon difference favoring the left side. It doesn't concern me at all. My fuel levels out in flight and it doesn't take very long. But I run on minimum fuel so more often than not I alternate wings high to make sure I have gas in there. How bad does your imbalance get? Test fly it to almost empty tanks and you may find you don't have a problem but rather the plane has a personality.
 
Mike,
The nylon vent line you mentioned, I believe, is only on the Long rang tanks. One less thing to worry about I guess.
Stewarb, on the last XC flight we did the right tank was around 8 gal and the left was 25 or slightly more when we landed.
 
Check your vents. You almost certainly have a pressure differential. I'll try to snap a pic of my vents tomorrow. They show tracks from being moved since the last paint job. No big deal.
 
Bought my 185 about a year and a half ago. Always had the same condition you describe, even taking special care to center the ball with trim in cruise. Installed a G500 early this year and the problem went away. I have noticed the "brick" used for slip/skid info seems to be very sensitive, more so than the traditional ball. Since the problem has now disappeared and both tanks generally stay within a half gallon of each other, my conclusion is that the instrument was askew, or perhaps there was parallax in how my eyes interpreted the ball and cage. Either way I am happy to leave the selector set to "both" full time unless I have other reasons to burn one tank first.

I do have a digital fuel quantity gauge that was installed and calibrated at the same time as the G500. I am well aware of the difficulties others have had with similar set ups and sending units, but mine seem to actually work pretty well. Though the quantity can vary from the engine monitor, it's never more than 3-4 gallons in disagreement at mid tanks, being most accurate in level flight at fuller and emptier tanks. (Within a gallon or so.)
 
Here's another thing that you can try. Blow into the vent tubes under the wing. If one doesn't blow freely, it is the vent check valve sticking. Or if it resists and then blows freely that's the culprit. They are spring loaded flapper valves with a rubber seal. Since the plane was sitting for a while and is high time it's possible. These valves are supposed to keep the fuel from running out of the vent on the wing which is parked low.

Joe Norris my 185 feeds evenly, so there is at least one which behaves.
 
Little Wing, Thank you that certainly made a point of having a accurate slip/skid indicator. Plane is on a grass strip but am going to refuel todat on the very flat cement fuel pad and will check the ball again.

Pete, Some time ago I fueled it and parked it with the right wing a bit lower and by the time I tied it down there was fuel running out the right vent. The maintenance manual talks about blowing into the tubes then putting the hose extension you blew into in water to be sure there bubbles cumming out of it.
Am heading to the airfield and will check that.

You gotta love the in depth technical trouble shooting procedures for complex problems Cessna offers.

Problem: No fuel quantity indication

Probable Cause: Fuel cells empty

Remedy: Service with proper grade and amount of fuel.
 
Tom3holer said:
Little Wing, Thank you that certainly made a point of having a accurate slip/skid indicator. Plane is on a grass strip but am going to refuel todat on the very flat cement fuel pad and will check the ball again.

Pete, Some time ago I fueled it and parked it with the right wing a bit lower and by the time I tied it down there was fuel running out the right vent. The maintenance manual talks about blowing into the tubes then putting the hose extension you blew into in water to be sure there bubbles cumming out of it.
Am heading to the airfield and will check that.

You gotta love the in depth technical trouble shooting procedures for complex problems Cessna offers.

Problem: No fuel quantity indication

Probable Cause: Fuel cells empty

Remedy: Service with proper grade and amount of fuel.
Click to expand...

Tom,

Dont knock it....those kinds of "trouble shooting" calls have no doubt been received by Cessna more than once. Many years ago, I worked on some high tech military electronics equipment. Every trouble shooting manual started with one page which said, in bold type "Before proceeding, move the ON/OFF switch to the ON position. If problem continues, proceed to page two of this manual."

It it was surprising how often we never got past page one.

MTV
 
Tom3holer said:
Going to fly tomorrow and will fill both tanks. The fuel pad is level so will check the ball for center; checked tire pressure today and it was equal.
Click to expand...


And if one tire is slightly bigger, or has a flat spot...

If you want accuracy, MCS has it correct: put the plane in level flight position as per the manual. Use levels to check.

But again, reality-- just trim the ball ever so slight to favor the fuller tank for a bit.
 
Went out yesterday and discovered a few things.

The vent tubes are not positioned exactly the same. The right tube is the correct 1.12" ish inches away from the strut. The left one, which burns slower, is 1 7/8". Doesn't seem to be a big difference but I don't know.
I got some vinyl tubing that fit over the vent tubes and blew into each one. The left tank had more restriction than the right but both were fairly easy to blow into.

On the fuel ramp I measured the wing tip to ramp distance on both wings and they were the same so I am guessing its level. The ball however was off to the left a bit.

I also noticed that on the ground during turnarounds that I would see fuel coming out of the opposite wing vent, right turn, left vent, is that normal with full fuel?

Will talk to my mechanic today and tell him what I found.

Yes, it is not a real big issue, but if it can be helped by a few adjustments that would be nice. We are installing a JPI FF gauge this week to compliment the JPI eng monitor.

Due to a bunch of issues I have only got a few hours in it so far but am really beginning to bond and enjoying flying it. It definitely flys different than my old 58 180 I had years ago. It seems to be more susceptible to x-wind gusts on T/O and landing than my 58 180 but I assume it is due to the larger dorsal fin.

T
 
Tom3holer said:
On the fuel ramp I measured the wing tip to ramp distance on both wings and they were the same so I am guessing its level. The ball however was off to the left a bit.

I also noticed that on the ground during turnarounds that I would see fuel coming out of the opposite wing vent, right turn, left vent, is that normal with full fuel?
Click to expand...
Place a level across the seat rails to ensure that the gas ramp did level the plane. Then adjust the ball in the T&B by loosening the screws and rotating the instrument. The screw holes should be slotted for this purpose.

The vent check valve in the left vent is not closing tight. With the tank full, it may also drip.
 
Most fuel ramps are sloped to promote drainage. Wingtip-ground distance means nothing.

The vent specification allows a tolerance of +/- 1/32". Your deviation is 3/4"?
 
Last edited:
Just a quick update
I have found that even when the Left tank is selected the fuel drains almost exclusively from the RIGHT tank.
Strongly suspect the fuel valve.
Started a new thread about fuel valve issues.

Tom
 
Problem solved.

It was the ck valve for the vent tube that had been pushed out of the nipple and fell to the bottom of the tank along with the crossover tube when a new vent tube was installed a few years ago.
Repaired it and hopefully it will work fine now.

Thank you all again for all the help.

Tom
 
Tom,

Congratulations on discovering the source of the problem, your troubleshooting, and thanks for posting the result of your investigation. It could help someone else down the road.

In past, I've done a talk called "Simple Airplane's Still Have Systems", and your plane is a classic case. Doesn't say Boeing on the side, but there's more to it than many think.

MTV
 
Tom3holer said:
Just a quick update
I have found that even when the Left tank is selected the fuel drains almost exclusively from the RIGHT tank.
Strongly suspect the fuel valve.
Started a new thread about fuel valve issues.

Tom
Click to expand...

this is still a problem
 
Dave,
Not sure if that was a question or statement.
Actually I have not flown it that much as the prop was off getting a reseal which tool WAY too long.
Was able to put a few hours on it and it seems to be much better but time will tell.

Tom
 
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