cessna fuel tanks

[triple7]

My buddy and I were discussing a few things last night, and the topic of cessna fuel tanks came up. We were reminiscing about a flight in a 172(2 hour flight) and how we worried about running out of gas, even though we knew we had plenty. the fuel gauges in the left tank kept reading close to empty. the right tank was over half full. Ive seen this often in cessnas. Is there any reason for why cessnas like to feed more out of one tank or the other, and would it make sense to switch to single tank feed verses both? what would happen on a long trip if i ran the left tank dry and had fuel in the right. would it still be kosher? there wasnt a blockage, siphoning, and both tanks were topped off prior to departure.

[JEP]

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and would it make sense to switch to single tank feed verses both?

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Absolutely. I have had that problem as well on xc's and you just switch to the fuller tank until they even out. Under no contition, would I ever purposely run one tank dry.

[BoilerPilot2007]

I've seen the same thing. Perhaps its a sensor problem? I can't see why one tank would guzzle gas incredibly faster than the other when the fuel feed is coming - supposedly equally - from both tanks.

[Ophir]

Typically this is due to two things. One is that when you the plane was on the ramp the fuel selector was not put on to only one tank. When this is the case the fuel will crossfeed to the tank that is lower. This is only a problem is your ramp is not level, like ours. I have arrived at the aircraft with 26gals in one side and 12 in the other. The severity of it depends of how uneven the ramp is. Secondly, if you fly uncoordinated the tanks will again crossfeed in flight. This is typically not the culprit becuase it is so uncomfortable to fly uncoordinated. But for a new student often times they don't know the difference.

My experience, after hundreds of hours in Cessnas on x-countries is that leaving the tank selector on both the whole time will even the tank levels faster than drawing fuel off of one. The crossfeeding will take care of the problem, just make sure the ball is centered. This is particularily true in 172's that are only burning 9-10gals/hr. If it was a TU206 then you should select one tank or the other due to a much greater fuel comsumption.

[DE727UPS]

Cessna fuel gages are junk. Never trust what they are telling you. From personal experience with my own airplane, they are accurate from 1/4 to E, that's it. You are much better off knowing your burn rate and exactly how much fuel is on board before you takeoff. I love those glass fuel dipper thingys.

As long as you are in "both", it wouldn't matter if you ran a tank dry.

[USMCmech]

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Under no contition, would I ever purposely run one tank dry.

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As long as you are in "both", it wouldn't matter if you ran a tank dry.

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If you were in "both" you probably wouldn't know if you did run one tank empty.

Running a fuel tank completely dry is completly harmless if it is done at altitude. Once the engine starts to sputter, you switch tanks, and about 15 seconds later it will smooth right up.


All the myths you have heard about contamination, and fuel pumps lubed by the fuel are false.

[gtpilot]

Fuel vent may be the culprit - if it gets bent out into regular airflow (even slightly), the ram air can cause a pressure differential that can cause the tanks to drain at a different rate. Just learned that recently.

[Dazzler]

I've had that happen to me on a XC before. The left gauge was reading much lower than the right. I switched to the right tank and ran on that for a while until the gauges were equal, then switched back to "both". Not a problem.

I have found that the needles in the Cessna fuel gauges do tend to swing about a lot more freely than those in the Pipers.

[bike21]

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Fuel vent may be the culprit - if it gets bent out into regular airflow (even slightly), the ram air can cause a pressure differential that can cause the tanks to drain at a different rate. Just learned that recently.

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Right on. I have an article (on paper only, sorry no link) that addresses this issue. It is due to the pressure differential from the fuel vent underneath the left wing.

I agree not to purposefully run a tank dry, there was a fatal crash last year that occurred b/c the pilot couldn't get the fuel selector back to the other side in time (Bonanza but same principle) Granted there should be plenty of time in cruise flight, but you never know!

I often burn off of a single tank in Cessnas during cruise as necessary - just don't forget to bring'em back to both before landing.

C182Ts and C206s are notorious for being out of trim during level flight and descents - make sure you teach to use rudder trim as a part of the cruise & descent checklist.

[EatSleepFly]

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Fuel vent may be the culprit - if it gets bent out into regular airflow (even slightly), the ram air can cause a pressure differential that can cause the tanks to drain at a different rate. Just learned that recently.

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A newer 182S that I used to instruct in had this problem bad. When the fuel selector was on both, it took an easy 5 gallons out of one tank, for every 1 out of the other. First the owner didn't believe me, then when he realized it, it took the mechanics forever to figure out why.

[NJA_Capt]

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I agree not to purposefully run a tank dry, there was a fatal crash last year that occurred b/c the pilot couldn't get the fuel selector back to the other side in time (Bonanza but same principle) Granted there should be plenty of time in cruise flight, but you never know!

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Bonanzas and Barons don't have a "Both" position. It is either "left, right OR off." There is also a mechanical "lock" to keep you from going to "off" accidentally. Pipers and Beech both have placards that read....take off and land on the fullest tank. This is to prevent the low altitude "tank dry" problem. There have been a ton of C210 accidents where they ran out of gas.....but had plenty of gas in the OTHER tank.
Knowing your fuel system is the best policy, not bypassing SOP because of uncertainty.

It was very standard in the small piston singles (old school) to run ONE tank dry to get max range/endurance. Ever get 5 hours out of a 40 gal Cessna SE?(Yes with VFR reserves). If you weren't trying to get MAXIMUM range, there was no reason to run a tank anywhere close to dry. Of course, it's a moot point when most flights are less than 2 hours and your avg endurance is 4.0.

Imagine.....all those years of flying with no GPS, fuel totalizers/flow meters, or moving maps. And if it didn't have two engines, it didn't need an autopilot.

[Seggy]

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Cessna fuel gages are junk. Never trust what they are telling you. From personal experience with my own airplane, they are accurate from 1/4 to E, that's it. You are much better off knowing your burn rate and exactly how much fuel is on board before you takeoff. I love those glass fuel dipper thingys.

As long as you are in "both", it wouldn't matter if you ran a tank dry.

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[bike21]

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I agree not to purposefully run a tank dry, there was a fatal crash last year that occurred b/c the pilot couldn't get the fuel selector back to the other side in time (Bonanza but same principle) Granted there should be plenty of time in cruise flight, but you never know!

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Bonanzas and Barons don't have a "Both" position. It is either "left, right OR off."

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Never said they did have "Both"; just meant that the tank ran dry and the guy could not get the selector back to the other tank in time before the engine shut down, then they apparently stalled and crashed - yes the pilot should have controlled the airplane, but the NTSB listed the following as a contributing factor "the pilot's inadequate in-flight planning/decision by his failure to switch fuel tank selector position which resulted in fuel starvation." Thats what I was meaning.