fuel tank overflow

fuel tank overflow

On my C-150-E, after filling up the tanks, a considerable amount of fuel leaks out the overflow.  When I check the tanks, the right one is low, and the left is pretty full.  Seems like it's going from the right to the left, then out the overflow tube.  The tanks have 2 different type of caps, and I'm wondering if the right one is not venting, thus when the sun heats up the wings and tanks, it is forcing fuel out of the right side into the left, and out the overflow.  Any suggestions?

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Re: fuel tank overflow

Search this site for Fuel Tank Venting.  Lots of discussion and comments about it.

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Re: fuel tank overflow

I'm assuming here cause I don't know the exact configuration of the C150e.  I'm assuming that it is similar to a C172M, i.e. there is no fuel overflow, the fuel tank caps relieves pressure due to vacuum and positive pressure.  Your description sounds like you are talking about the tank vent that has a check valve, which seems, in your case, to not be sealing closed preventing fuel from leaking out.

As the tank pressure increases due to fuel tank heating, the check valve in the fuel vent should close tighter preventing leakage and allowing the pressure to rise to the point that the fuel cap vents relieve pressure in the tank(s).  So I am guessing with all these assumptions that the problem is in the check valve in the tank vent and not the fuel caps...

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Re: fuel tank overflow

Are you parked on a sloped surface?

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Re: fuel tank overflow

Herb:  You suggested to search this site for fuel tank venting.  What site?
Will

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Re: fuel tank overflow

Barry,  I don't know if the 150-E has a check valve, but I do know that there are 2 different types of caps.  One with raised tabs, and the other has ridges around the cap for grip.  Neither one has that little red supple rubber underneath like the 172's i've seen.  That is why I am wondering if the caps are not vented, thus causing the pressure to build up forcing the fuel out of the tank vent or overflow, whichever it is.

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Re: fuel tank overflow

JimJ, 
     No, it is not on a slope, but I wish it was, that would explain everything.

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Re: fuel tank overflow

You mentioned the caps are not identical.  Try to determine which one is vented and which one isn't.  If the non vented cap is on the right side, pressure could build up there in hot weather after filling the tanks, forcing gas to the left, and then out the overflow.  If that is the case, maybe the caps are reversed--check the POH to see if thats the case and switch them if it is.  If that is not the case, then the plane must have a slight "lean"-- either the ground isn't level or one wing sits lower when parked.  Is a tire low on air?   One note--Cessna's are famous for overflowing fuel on hot days after filling the tanks--hence, the overflow vent (valve).

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Re: fuel tank overflow

Thanks, I'll check the caps again, and reverse them to see what happens.  As I mentioned, I didn't see any rubber flap indicating a vented cap on either one.  It is not leaning.  And, finally, I checked the POH, but it doesn't even show the overflow valve in the fuel system schematic, much less a valve for the overflow, or any dialogue about the gas caps.

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Re: fuel tank overflow

Didn't you say you saw the fuel came out of the "overflow" or am I reading too much into your description?  If you are not seeing the fuel coming out of the fuel vent below the bottom of the left wing, then I agree that the right cap is not a vented cap and the fuel is venting out the left fuel cap's pressure relief.  The level in the left tank right tank would be at the approximate level of the crossover pipe between fuel tanks.

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Re: fuel tank overflow

Sorry for the confusion and terminology.  The fuel is coming out of the fuel vent under the left wing.  I thought the correct name for it was the fuel overflow tube.

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Re: fuel tank overflow

Hi Will

This used to happen in my friends 182 every time that he filled it.
It was so bad we were scared of starting up in case we started a fire. He used to fill right up - now he fills to just below the bottom of the collar on each tank and that has solved it. We were told that it was related to ambient temperature, and 100ll increasing in volume as temperature rises.

Some more fuel advice - if this aircraft is new to you, change the fuel caps. Quite apart from maybe helping with this problem there is another reason -  My 172, which burns 8gph suddenly started using 12 - 14 gph. The fuelcap seal was worn and the fuel started siphoning out. If I had been flying a long cross country when the problem started I'd have run out of fuel. New caps are only $40.00 each - cheap insurance and great peace of mind

Tony




> Sorry for the confusion and terminology.  The fuel is coming
> out of the fuel vent under the left wing.

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Re: fuel tank overflow

Thanks for the help.  Are these special caps, or can I use vented caps from an auto parts store?

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Re: fuel tank overflow

Will, I'm afraid we can only wish!

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Re: fuel tank overflow

Tony; Where do you get your caps at?

   Dave

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Re: fuel tank overflow

Hi David
I replied yesterday but my post didn't show up - trying again:

AOG Air Support
6095 Airport Way
Kelowna BC
Canada
V1V 1S1

Tony

David Kalwishky wrote:

> Tony; Where do you get your caps at?
>
>    Dave

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Re: fuel tank overflow

The condition you are having is most likely NOT from fuel caps.The caps can cause problems,but I doubt if replacing them will correct the problem.
The vent valve is located on a "dogleg" tube on the upper front portion of your pilots side tank.This valve can sometimes inadvertently get twisted,and subsequently put the valve in the fuel itself.proper alignment is to have someone observe the valve with a flashlight,and extension mirror to see if it is indeed in the"air" portion of the tank(basically touching the top of the tank) this is designed to keep the valve in the"open air" area of the tank.If it is not in the upper area,an adjustment of the outlet fitting is required.Pressure inside the tank is supposed to be relieved by this valve,but if it is below the upper fuel level it will vent fuel instead of vapor.This valve is about 100.00,and a real bugger to replace.A much cheaper soultion is to refrain from completely filling the pilots side tank.Cross feed will effect the fuel level,but it rarely wil make both tanks exactly even.Were talking maybe 3 gallons less than you normally would,and your "leakage" should subside.

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Re: fuel tank overflow

Wednesday evening, I switched the caps (one is a vented cap, and the other doesn't seem to be), filled and measured the level in the tanks.  I'm going by the airport today, and I'll check the level in each.  In the past, the right one was usually lowest, so I'm interested to see what the result if any will be from switching the caps.  I will also look into the valve placement as last suggested.

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Re: fuel tank overflow

Will,
I suggest that you don't fly the airplane with the caps switched  unless you can determine that the switched positions are the correct positions as recommended by Cessna.  You don't want a tank to implode as you descend due to the lack of air to equalize pressure (or have fuel exhaustion due to a vacuum in a tank)! Don't depend on cross-feeds between tanks to keep you out of trouble.   I know that for C172's, Cessna no longer makes a non-vented cap; if you order a replacement cap, there is only one---vented.  You might want to check into having 2 vented caps instead of one.

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Re: fuel tank overflow

Will,
If memory serves,the fuel vent valve is located in the fuel tank portion of your parts book.I noticed that someone had given you a source to purchase fuel caps in canada,this is fine,but any Aircraft parts dealer either will have,or can order them in your locality.
Im located in memphis tenn,and have a really good Cessna parts source here.I bought both new caps and the vent valve from her.If you want her number Ill be happy to provide it...drop me an email direct to: This e-mail address is being protected from spambots. You need JavaScript enabled to view it and put fuel caps in the subject line,and ill forward the info...Must warn you,replacing this valve pretty much requires removing the Pilots side tank and ALOT of patience... most A&Ps will loathe the idea of replacing this,as for most,one time is too many......tailwinds

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Re: fuel tank overflow

Well, here's the latest scoop.
When I went back to the airport on Friday, I didn't see any fresh fuel on the ground after switching the caps.  And, the levels were even, unlike normally when the vented cap was on the right, which was always lower in level than the left.  When I went back on Sunday to fly, there was very little difference.  I flew to the Mid-Atlantic fly in at Lumberton, NC from Lexington, NC, and back, totaling 2.3 hrs. of flight.  Thank goodness that the tanks didn't implode.  If I would have gotten the message from Bob prior to going, I would not have left the caps switched.  But, everything seems to be fine.
I know it doesn't make sense, but the level didn't drastically change since switching the caps, and I'll keep watching it to determine my next course of action.

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Re: fuel tank overflow

Hi Will,
I'm glad your tanks didn't implode too!  That could happen if pressure gets out on the way UP but can't get back inside on the way down.  Why don't you just put a vented cap on each tank like I did?  It solved my problem of uneven draining in my C-172.  How was the Lumberton fly-in?  I was thinking about going (I'm in CLT). Was it geared to exp. aircraft, homebuilts, or what--just curious.
Bob

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Re: fuel tank overflow

Will,

Here is the website for Yingling Aviation in Wichita,KS.  I bought my Cessna vented fuel caps from them for around $21.00 each, and got them within a day or so.

http://www.yinglingaviation.com/parts/index.html

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Re: fuel tank overflow

Thanks for the information about yingling.
I'll get in touch with them about another cap.

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Re: fuel tank overflow

Bob,
    Thanks for the info.  The Lumberton fly in was really good on Sunday when we went.  What the pilots and planes did was beyond my belief.  There was a lot of airobatics, military planes, and the master of disaster truck racing and beating a high speed bi plane.  The food and concessions were varied, good, and fairly priced.
There were not many vendors there, to my dissatisfaction.  I plan on going back next year if they have it again, which I think they will.
Will

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