The International Cessna^® 170 Association

Yesterday I filled my tanks on my 170B and I noticed that out of the 28 gallons one tank took about eight gallons more than the other. I have always had some difference but not that much. Here are my questions.

Could the venting on one my fuel caps be restriched? I looked and it does not seem to be.

Will the engine run drawing fuel from only one tank if the other runs out? It should, but is there a way to test this safely?

Thanks,

Larry

Larry I run my 170B on one side or the other all the time. No problems and no restriction from doing so.

Fuel flow on the 170 systems seems to be a black art sometimes. Fuel flows between on tank and the other which ever is lower then you go and fill and the plane looks level but it's not.

I wouldn't spend to much time thinking about this. Now if one tank completely drained will the other did not then I'd start poking around.

I read Larrys question as: If I'm running with the fuel selector valve set on "BOTH" and a tank runs dry, will fuel continue to feed adequately from the other tank?

In my experience, YES. I have purposely set the fuel selector on single tank and run a tank empty until the engine quit and then turned the selector to "BOTH"and the engine recovered in a matter of a couple of seconds.

It has always been my policy to switch to the other single tank when either gauge gets down to 1/4 full. I then run that tank dry knowing that I now have 1/4 tank remaining. I do, however, make it a point to try to refuel before I get that point unless I'm in very familiar territory. I prefer to land with at least a hours fuel unless I'm "real local".

N9149A wrote:Larry I run my 170B on one side or the other all the time. No problems and no restriction from doing so....

I'll bet that's a slight mis-communication. (Takeoff and Landing should always be performed on BOTH, per placard PN:0505006-1.)

gahorn wrote:

N9149A wrote:Larry I run my 170B on one side or the other all the time. No problems and no restriction from doing so....

I'll bet that's a slight mis-communication. (Takeoff and Landing should always be performed on BOTH, per placard PN:0505006-1.)

I wasn't thinking about landing and taking off. Funny thing you have to have the selector on both for those maneuvers but you don't have to have any fuel in either one of the tanks meaning one could be empty. You would of course have to have some fuel in at least one tank to depart.

How does your airplane fly? Does it keep the ball perfectly centered. Have you ever jacked the airplane up and perfectly leveled it on the lateral axis and then checked the installation of your ball bank indicator? If the airplane is flown perfectly level, fuel flow should be equal between tanks. Chances are that aint going to happen.

I do leave it in "Both" all the time. I was never taught to do anything different. I had a Champ for years and flew it the same way. Both tanks on the Champ usally drew down fairly close. I will do some expermenting in the next flights. I just have never been exposed to this before in all my years of flying and wanted to make sure that there was nothing wrong mechanically. Thanks

Larry

Uneven fuel useage has been discussed previously at:

http://www.cessna170.org/forums/viewtop ... uel#p24083

and at:

http://www.cessna170.org/forums/viewtop ... fuel#p9094

Basically, one of your tanks is crossfeeding the other via the vent-line. In other words.... BOTH tanks are feeding your engine,...but one tank is replenishing the other and keeping it fuller until gravity and head-pressure breaks the siphon-action and they return to both feeding individually. Bottom line: Don't worry about it. If the selector is in BOTH....any tank with fuel will feed the engine.