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Topic Options
#73922 - 03/31/12 04:09 PM uneven fuel flow
mattcyyz Offline
New Member

Registered: 03/23/11
Posts: 1
Loc: ontario canada
This is my first post on the cessna 172 club forum but i have read many threads and have gained alot of useful infromation wich has helped with my purchase and restoration of a 1969 172 K so thanks to everyone on the site!! My 172 sat in a hanger for ten years so naturally there were some bugs to work out I have basically fixed or replaced anything that could be affected by age or decay including complemply overhauling the engine, prop replacing the lord mounts, starter, alternater, mags, and wiring harness. I have also redone the panel. But I'am now finding that i have an uneven fuel flow from my left and right tanks. my left tank drains at a three to one ratio compared to my right tank. Is this normal or maybe user induced? i have yet to take the tanks below half. any advice or info any one would have will be greatly apprcieted

thanks

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#73923 - 03/31/12 04:15 PM Re: uneven fuel flow [Re: mattcyyz]
California Flyer Online   content
Diamond Pilot

Registered: 10/21/09
Posts: 5556
Loc: Groveland, California
Hi Matt! Glad you have found this club to be a useful place for knowledge.

My 2000 SP model also draws fuel unevenly during the first third of the flight. It will draw from the left tank until about 10 gallons are gone, then it will start drawing from the right tank. Things even out from there, though sometimes I will fly with the selector switched to just the right tank for a bit to balance things out. So far it hasn't been a problem for me, it's just one of those quirks I have gotten used to. When I was renting, the other Cessnas in the rental fleet all did that too, to varying degrees.
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#73924 - 03/31/12 04:27 PM Re: uneven fuel flow [Re: California Flyer]
Bigdoggh Offline
Gold Pilot

Registered: 05/26/11
Posts: 1710
Loc: Georgia
Mine does the same.
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#74005 - 04/01/12 06:56 AM Re: uneven fuel flow [Re: Bigdoggh]
wrecksum Offline
SVP Public Relations
Platinum Pilot

Registered: 09/26/10
Posts: 2704
Loc: Dominican Republic
Same here.
Left tank drains faster.
On long legs I equalise the tanks but it's just one of those quirks it seems.
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#74008 - 04/01/12 08:05 AM Re: uneven fuel flow [Re: wrecksum]
Bigdoggh Offline
Gold Pilot

Registered: 05/26/11
Posts: 1710
Loc: Georgia
Actually, mine drains the left tank faster on full tanks. Like Susie, the burn evens out as more fuel is consumed. Since most of my CC are over 5k, I switch tanks as well.
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#74010 - 04/01/12 08:13 AM Re: uneven fuel flow [Re: Bigdoggh]
Dr Nick Offline
Bronze Pilot

Registered: 04/27/11
Posts: 721
Loc: Nebraska
My 69 does this as well. Evens out as you draw more.

The left draws faster because the left is where the fat guy controlling the plane is seated so that your more evened out on landing. My theory anyways.
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#74017 - 04/01/12 10:01 AM Re: uneven fuel flow [Re: Dr Nick]
Don Tedrow Offline
Platinum Pilot

Registered: 07/16/10
Posts: 3169
Loc: Bastrop, TX
Originally Posted By: Dr Nick

The left draws faster because the left is where the fat guy controlling the plane is seated so that your more evened out on landing. My theory anyways.


+1! Works for me. grin

My understanding of the issue is that both tanks are feeding properly, the issue is that the main fuel vent is below the left wing, and both wings have dihedral. What that means is the slightly higher head pressure in the left tank is forcing fuel through the crossover line to the right tank. When the fuel level in the left tank gets to about half full, then air, not fuel is flowing to the right tank, and fuel levels even out. That's from the CPA tech notes, and is exactly how my Skyhawk acts. They do recommend that you double check the exact positioning of the fuel vent behind the left strut. There are some precise measurements for that vent to act properly and to avoid blockage in icing conditions. +/- .03" in my service manual.
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#74026 - 04/01/12 12:04 PM Re: uneven fuel flow [Re: Don Tedrow]
Dr Nick Offline
Bronze Pilot

Registered: 04/27/11
Posts: 721
Loc: Nebraska
Originally Posted By: Don Tedrow


+1! Works for me. grin

My understanding of the issue is that both tanks are feeding properly, the issue is that the main fuel vent is below the left wing, and both wings have dihedral. What that means is the slightly higher head pressure in the left tank is forcing fuel through the crossover line to the right tank. When the fuel level in the left tank gets to about half full, then air, not fuel is flowing to the right tank, and fuel levels even out. That's from the CPA tech notes, and is exactly how my Skyhawk acts. They do recommend that you double check the exact positioning of the fuel vent behind the left strut. There are some precise measurements for that vent to act properly and to avoid blockage in icing conditions. +/- .03" in my service manual.


Yep, that to.
_________________________
Life is tough, I got your back!

1969 C~172K N79105

http://www.linnchiro.com


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#74036 - 04/01/12 03:58 PM Re: uneven fuel flow [Re: mattcyyz]
Jim_1 Offline
Gold Pilot

Registered: 04/06/11
Posts: 1879
Loc: ON, Canada
Hey Matt

Welcome to the forum.
I like yourself drove myself crazy worrying about this trying to determine why my left tank emptied so much quicker than the right. Many experienced folks here and they also aided my in realizing its absolutely normal.

Good luck and welcome to the forum.


Jim - also from ontario
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#74043 - 04/01/12 04:46 PM Re: uneven fuel flow [Re: Jim_1]
joelaff Offline
Bronze Pilot

Registered: 04/08/11
Posts: 626
Loc: Missouri, USA
Cessna Pilot's Association has a Tech Note on this issue... And it is, as othes have said, normal.


Edited by joelaff (04/01/12 04:55 PM)
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#74047 - 04/01/12 05:12 PM Re: uneven fuel flow [Re: joelaff]
tedh Offline
Safety Pilot

Registered: 03/13/11
Posts: 50
Loc: Dripping Springs TX
The 152 does the same. I think it is caused by uneven air flow across the filler caps, which is caused by the rotating air of the props.

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#74095 - 04/01/12 10:45 PM Re: uneven fuel flow [Re: tedh]
Adger Smith Offline
Second in Command

Registered: 02/27/12
Posts: 188
Loc: East Texas
Ditto: my 1961 172B does it too....
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#74272 - 04/03/12 02:14 AM Re: uneven fuel flow [Re: Adger Smith]
RixxoN Offline
New Member

Registered: 05/13/11
Posts: 1
Loc: Germany
My 1976 172M draws left faster too

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#74367 - 04/03/12 09:36 PM Re: uneven fuel flow [Re: RixxoN]
RodneyHooverCFI Offline
The Cessna Sensei
Gold Pilot

Registered: 02/16/10
Posts: 1645
Loc: Pasadena, MD
Don Tedrow's post on the reason for uneven fuel flow is spot on. If they had an identical vent in the same location behind the right strut, it would help, but not necessarily fix the issue 100% as there are other contributing factors.
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