Left tank fuel burn faster than the right

Left tank fuel burn faster than the right

I have a fuel injected 172SP with an engine driven fuel pump (not sure that's relevant but thought I would mention it anyway).

Here's the deal.  On long, straight and level cross country flights the fuel burn from the left tank is significantly more than the fuel burn from the right.  The left tank can be 1/2 empty when the right tank hasn't even come off the peg. If you get to this stage and put the fuel selector valve to burn from the right tank only it draws fuel just fine and continues to purr along so there is no starvation as far as I can tell.  I talked to one guy who said it might be the fuel vent that's causing the problem although he did not give any specifics as to what to do to fix it.  If I'm just out in the practice area or shooting approaches the fuel burn is mostly even.     

Mike Banner
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Re: Left tank fuel burn faster than the right

Mike,
Sound like it could be flight rigging. Your autopilot will "overcome" minor flight rigging issues, masking them. So, next time you go for a long cross country fly the plane yourself. Is the ball center? Wing heavy? In other words, will the aircraft maintain a heading, hand and feet off, ball centered?
I've seen rigging cause this before, but you should look through these forums; this has been recently discussed, so you might get other ideas.
Del

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Re: Left tank fuel burn faster than the right

I have a 2002 182, and also experience a faster draw rate from one tank (I think the left).
Anyway, was talking with my A&P this wknd, and he had read an article about the subject. Seems that if you view the plane from the front, it is apparent that the vents are not positioned equally relative to the wing struts. One of the vents is more behind the wing strut than the other. This results in different wind/air pressure at the vent, thus a different draw rate.
I can see the difference on my plane. Maybe that's the cause, maybe not. In any event, I have decided to leave as is for now.
Steve

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Re: Left tank fuel burn faster than the right

This is normal as the left tank has an underwing vent and the right side does not although both have fuel cap vents. You can test it with cups and a straw and get the same results.

RPSumner
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Re: Left tank fuel burn faster than the right

I believe this behavior is common to many Cessnas, especially those with long range tanks.  I've noticed that my 182 is often a gallon or two lower in the left tank than the right.  The way the vent system is designed, fuel can siphon from the left tank to the right through the vent crossover when both tanks are full and will continue to do so for some time because there is so little dihedral in wings.  Since only the left tank is vented to the atmosphere, there is more pressure there than in the right.  You might check the positioning of the vent tube relative to the strut also.  I think Cessna issued a SB about this some time ago and the positioning is critical - just a tenth of an inch lower or higher makes a difference.

Randall Boan
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