I posted this on the famously quiet Skywagons.org and got nothing. It’s famously quiet, after all. . . .

The airplane in question is a 1981 C185, SN 4181. Here’s the post:

When I set my fuel selector on Both, I always burn more from the left. When I set it to Right, I burn from the right but the left still goes down considerably. Looking through the service manual and talking it over with my mechanic, I’m pretty sure the fuel selector has an internal leak, such that the left tank is never completely shut off. There are no fuel leaks to the outside and nothing leaking into the cabin.

The airplane is having its annual right now. Is this something to fix or something to live with?

Assuming I get it fixed, how hard is it to do in the field with an O ring kit, vs doing an exchange or some such with MacFarlane?

Stuart,

I agree on the quietness of skywagons.org. Its a shame.

My plane does exactly what yours is doing. If I put equal amounts of fuel in the hangar and leave the fuel will creep to the right side. The fix was put the fuel selector in L or R when parked. According to the fuel truck guy at the airport, its a common thing amongst Cessnas....
Not happy with that answer, I got my mecanic involved and according to him he adjusted the valve to prevent excessive fuel cross over. I still get cross over, but less of it.
The good thing is that you don’t have a fuel leak nor are dumping fuel overboard. On an hours flight I have about a gallon difference between L R consumption.

Let us know what you find out.

Rgs

Patrick

While I’ve not had a fuel selector problem,I’d suspect your problem with uneven burn on both is due to either the ball not being centered in flight or your fuel vents needing adjustment. If you need the service manual pdf let me know.

Andy

Stuart,

Best advice I can give you having owned multiple Cessna singles over the years: Get use to it.

My 180 does the same thing to some degree. The '75 Skylane I had a few years ago, did it to excess. On that airplane one tank, the right I think, came down at three times the rate of the left. Put the valve on right and it came down at twice the rate. At some point, when the right tank got down to about 1/3, it began to even itself out.

The answer is in the venting system that someone knowledgeable explained to me once. It was a valid explanation with no real cure so I just quit worrying about it.

Jg

My two 182s do the same thing.

I’ve learned to live with it.

That’s not it. When the selector is set to Right, I burn fuel from both. The only connections between the tanks are at the top crossover vent, which isn’t the problem. with half tanks and level flight, and at the fuel selector. For uncoordinated flight to be to blame, I’d have to be in knife edge. If the right vent was plugged, I still wouldn’t get flow from the left tank with the selector set to Right. The crossover vent would also provide air to the side with the blocked vent.

Let me make sure we’re saying the same thing. Does your fuel level go down in both tanks when your fuel selector is set to one side only?

Let me make sure we’re saying the same thing. Does your fuel level go down in both tanks when your fuel selector is set to one side only?

The CPA has tech note that does a pretty good job explaining this. In short, this is caused by fuel in the crossover vent.

The crossover vent can convey a serious amount of fuel from side to side. Each little slosh in the tank puts a slug of fuel in that line, to be carried over by any slight pressure differential betweeen the vents. This occurs even if you are only burning fuel from one tank.

You can mess around with the vents and try to make it better, but you'd be my hero if you made it perfect. (By mess around I mean follow the guidance in the MM to adjust them)

If you still feel you have trouble with the valve, be sure to check out McFarlane, they have rebuild kits that might help.

did you stick the tanks after flying it? the fuel tanks senders and gauges are also highly unreliable.
As the others have noted I also fly mine on both and ignore the difference in the gauges.

Andy

There is a lot of advice here to say it’s not the fuel selector.

But if you find any good reason to think your fuel selector needs an IRAN, just do it. That is an incredibly critical item. Just ask the guy who had the knob come off in his hand while in between tanks on an A36

Let me make sure we’re saying the same thing. Does your fuel level go down in both tanks when your fuel selector is set to one side only?

Morning

1. Are your fuel vents 100% correct ? the service manual calls for them to be + - .03 inch

2. you mentioned when at 1/2 tanks in flight ?
Do you have long range tanks ?
If so the long range tank installation calls for an extension to the cross over line
the extension extends the the line further inside of the tank.( I think almost half way
into the tank. )

3. Also remember that the return fuel from the header tank returns fuel up the
Left side door post , and is tied into the cross over line , this can affect the fuel
levels in flight. ( wings level , and co-ordinated flight for even return fuel. )

4. Are your fuel senders accurate ?

John

Quick way to test. On the ground move selector to right tank only and drain tank thru gascolator. If left tank drains too, you know the fuel selector is not aligning properly. For what's worth I have a slight imbalance both inflight and after sitting on ground with mine.

I don’t understand this. The crossover goes between the very highest points in the tanks. At half fuel, that’s several inches above the fuel level. How would a significant amount of fuel cross over? And why would it always go the same direction?

This is my fault for trying to balance fuel flows. But with it on Both, the left side gets down to 1/2 or less before the right one comes off the peg.

Planning to call McFarlane today but they’re on Central Time so it’ll have to wait a bit.