even gas usage between tanks

M

mikedavis

New member
I bought a 73 citabria 7gcbc. The left tank always uses more gas than the right. Tanks are venting. Tanks to do not even out even when sitting in hangar for a week. Has anyone else run into this problem?
 
I have only had my 8KCAB for a little over a week but I have noticed the same thing. I did find one quote in the flight operations manual which may explain the cause:
"Fuel tank caps are not vented and must seal completely to prevent a difference in fuel level between the two tanks."
The tanks are vented so I don't see how a fuel tank cap that is not sealing could affect the fuel level but maybe someone else can explain that.
 
I suspect the difference in fuel level refered to in the flight operations manual is for an an inflight situation where the leaking cap gasket allows a slight vacume to be drawn on one tank.

I assume that you are not just talking fuel gage readings. On the ground (and in the air) my gages never read the same, but it is the gages, not the amount of fuel in the tank. I have confirmed this with actual fueling tests.

Also, I assume you have alternated which tank you fill first. I have noticed that when I fill the tanks, the first one that I fill will always take a slight bit more fuel than the second. This is because fuel is draining from the first to the second until I get around to getting the second tank filled. I never have noted the exact amount of difference (and it would be time dependent), but I have the impression it's about a half gallon with my usual procedure.

Hope this helps.
 
If the cap leaks in flight, you WILL have uneven fuel burn.
The Vent system is ment to stabilize an equal amount of pressure in both tanks.
 
I'm sure it has to do with sealing because one of my caps didnt get put on tight one time and 18 gallons of gas was GONE in 25 minutes!!!!!! :(
 
One other thing, since you said it does not even out after sitting, is the airplane level where you park it? It should have equal fuel quantity in each tank after sitting WITH THE WINGS LEVEL for a few hours, if not I would check the fuel level with a stick, if the stick check is good then your guages are not well callibrated.
Bill Becker
 
My 8KCAB Decathlon always seems to burn faster out of the right tank. I know it's not guage error because I dip the tanks before and after fueling and it confirms what the guage is saying. Another strange phenomenon is after fueling both tanks to an equal amount of 1/2 full, pushing it into my hangar(a flat surface), and then coming out a week later and noting less fuel indicated in the right tank than previously noted.
 
So can the engine run out of gas on a long flight when one tank gets low or empty? Or does the other tank start gravity feed the engine despite a poor seal on that fuel cap? I am presently experiencing that problem. I just ordered a couple non-vented fuel caps but I won't get them until next week and I am planning a long trip in the weekend. I know after I land the fuel start flowing from the full tank to the near empty one so no problem with cross-feed.

Again, should we worry about fuel starvation even though there is one tank still full with a poorly sealed fuel cap?

Thanks

Bruno

Yellowknife
 
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