The International Cessna^® 170 Association

I have looked at the threads on this topic but still need help. Here’s the tale:

When I first got my 170B about 6 months ago I had very uneven fuel flow, with left tank emptying much more quickly than right. Was told that
this was “normal” or at least, common. On the ground the engine ran ok when selector on either right or left tank. I was suspicious about the
ground test, and sure enough with higher throttle settings in the air the engine would quit when the selector on Right.Next emptied tank and looked at fuel screen associated with quick drain near wing root on bottom of right wing. Nearly occluded by mud and the bodies of several
Mud daubers!

After cleaning the strainer screen it runs ok on Right tank, but still burns much more from the Left tank. I have taken to having the selector on Both
While in the pattern (which is the majority of my flying as I am still working on my landings) and when out of the pattern switching the Selector to the Right tank. Despite this technique, today at fill up the Right tank took about 1.5 gallons and the Left took over 11 gallons!

This can’ t be right.

I plan to repeat the exam of the fuel strainer of the slower draining right tank to see if there are more bug bodies,
but am looking for other possible causes of this excessive discrepancy.

Any suggestions from other owners?

Bill Drury

I would be very concerned about that fuel discrepancy between wings . I would be checking my vent system very closely also and checking for flow at different points of the fuel lines . There may be a restriction at a pipe join or bend. Those bugs can make a big difference in the fuel lines . I do not know how old your vent lines are but we had a case when the vent [rubber] line looked good on the outside and air could be blown through but when the tank was full the lining of the rubber hose would collapse internally and semi block the vent . Please note . This aircraft had both tank caps fitted with vent valves also . But would only suck fuel from one tank until the other tank was nearly empty .
A “. Theory” was put forward that the lower pressure on the upper wing has a tendency to hold those little red rubber valves in the tank caps closed .

Don’t look at the gas gauges! Lean properly and fly 4 hours then fill the tanks. Repeat.

No, seriously, mine does exactly the same thing, except the engine quitting part. I run in “Both” position.

Of course, make sure all hoses and screens are in good shape too.

Your experience with clogged fuel line/strainers should be cleared up first. Check them all, and blow them all clear.

When finished determining your system is healthy... EXpect one tank to empty faster than the other. It’s a matter of the overhead vent line siphoning fuel over to RE-FILL the other tank ...until sufficient vacuum is formed to break that siphon.
I operate on BOTH always. I usually find my right tank empties faster than my left. Both of my tanks have vented caps.
At least ONE tank...the right one...is REQUIRED to have a vented cap by AD note.

A search of this forum will provide a more detailed explanation but the bottom line is the same.

Mine does the same thing, it’s common from my research.

Progress report: Removed the slower-draining tank and found some material (possibly more mud dauber nest) in the inlet to the tank itself
nearly completely blocking air flow. Rest of vent clear.
Will put the plane back together and see what happens. Will report results.

Bill

Good find. 1.5 gallons vs. 11 gallons isn't right!

Bill Drury wrote:Progress report: Removed the slower-draining tank and found some material (possibly more mud dauber nest) in the inlet to the tank itself
nearly completely blocking air flow. Rest of vent clear.
Will put the plane back together and see what happens. Will report results.

Bill

Even a completely-blocked vent inlet to the tank should not prevent a vented cap from doing it’s job.

Final progress report: After a 2.3 hour flight I refueled; about 17 gallons total; about 10 from left tank and 7 from right tank. No visible fuel leaks.
I consider this an acceptable discrepancy and will move on to other issues. Thanks for all the member inputs!

Bill