Cessna 182p tank siphoning

[MikeLima]

What are the possible causes for the left tank to drain into the right tank when fuel selector is set on both... to the point where right tank fills to overflowing? Happens when flying, not sitting.

Thought the first time must have left the right cap loose but apparently that wasn't it. Fuel will feed from both tanks if selected individually. Could the fuel bladder being partially disconnected from filler tube cause this?

ML

 

[Clip4]

What are the possible causes for the left tank to drain into the right tank when fuel selector is set on both... to the point where right tank fills to overflowing? Happens when flying, not sitting.

Thought the first time must have left the right cap loose but apparently that wasn't it. Fuel will feed from both tanks if selected individually. Could the fuel bladder being partially disconnected from filler tube cause this?

ML

There is a vent interconnect between the tanks. It is normal until the fuel levels are about 60% in both tanks.

 

[Pilawt]

If the seal in the right tank cap is bad, suction from the top of the wing (and good morning to you, Dr. Bernoulli) can pull fuel through the interconnected system.

 

[Zeldman]

I used to fly a 182 that did the same thing. Turns out when parked on a slightly sloped ramp the fuel would go from the uphill tank to the bottom hill tank. I just turned the fuel valve off and put a BIG note on the flight can and the yoke.

 

[swingwing]

I just turned the fuel valve off and put a BIG note on the flight can and the yoke.

Not sure about all 182s but the late model legacy aircrafts (P,Q &R) cross feed in the off position. You need to put the fuel selector to either the right or left position to prevent cross feeding.

 

[Hunter]

If it is blowing out of the cap and off the back of the wing, you need new rubber gaskets in your caps. It is a cheap fix, I had the same issue in my J model. Also, your vent tube might need adjusting. Mine still cross feeds every flight.

 

[Shawn]

Very common an know issue...I fly switching 50% on R and 50% on BOTH....don't think I have ever flown on L tank to keep draw balanced.

Problem is in how the venting system is deigned, but other problems like poorly sealed caps can amplify the problem.

 

[denverpilot]

Cessna Pilot's Assn has an excellent paper on why this happens, and fixes.

And you can chase them for the rest of your life and they'll still do it.

Things to check:
- Cap seals
- Vent line check valve
- Vent tube EXACTLY located in reference to the strut as per the Cessna SB on the topic

And a few other things.

Thing is, and someone mentioned it above -- there's a cross over vent about 2/3 of the way up the tanks, and it doesn't matter what you do with the selector valve... if the airplane is at all off of level or the pressure from the only air vent (left side) is higher by a tiny bit than it should be, or the moon is waxing gibbous... fuel will push from left to right until the cross over vent line is below the fuel.

 

[q5kacom]

As others mentioned, its normal and you get used to putting more fuel in left tank.

 

[denverpilot]

I learned this week that MacFarlane makes a vent line with an upward and then downward bend in it. Doesn't help the tank to tank transfer but does help the common siphoning overboard problem. And like a lot of their gadgets, fixes things Cessna did wrong.

 

[Dan Thomas]

I learned this week that MacFarlane makes a vent line with an upward and then downward bend in it. Doesn't help the tank to tank transfer but does help the common siphoning overboard problem. And like a lot of their gadgets, fixes things Cessna did wrong.

The oldest 180s (and 170s) had the tank vent on the top of the cabin roof near the left side (170's in the center). It stuck straight up and curved forward, and fed the air into that vent crossover line. Siphoning from one side to the other was impossible, though a small flow across was still possible if parked on a lateral slant and the tanks were full enough. No big deal if the cap seals were OK. No underwing vent for fuel to run out of, either. It had the old problem of being subject to icing or bug-clogging, but worked better than the later venting systems. Adding vented caps as per AD 79-10-14R1 fixes that.

You can see the vent sticking up on this one: