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Baffled??? 12 gal per hour or a leak?

I made my first long / not so long trip last weekend, Gettysburg Pa to Toronto Ont Canada and back 650miles return. After calculating my time in flight my fuel consumption seems to be just under 12 gal per hour. I am running an 0-320 w/carb. I landed and got fuel (top to about ? inch below the filler neck) about a half hour before landing back at Gettysburg and putting the plane away. When I went out to the airport yesterday I checked the full levels and was baffled. I used the left tank coming back from fuelling the other night and it was down about 5 gal +/- but the right tank was also down about 2 gals. I must have a leak? I looked every ware and could not find any indication of a leak. The only thing I could think of was that I was losing the fuel through the filler caps in flight. Is it possible to lose that much fuel if the caps are not tight. I can open them easily with my finger , in fact I can rotate one after it is closed. If so why is there no indication as in blue stains est.
 
Fuel Flow

The tiniest seep on my wing or caps tanks are quite evident. You can burn close to 12 if you run full rich and hard.
 
Depending on where you fueled and the tempurature of said fuel it could have shrunk in the tank. Fuel expands and contracts a lot with temp. I don't know how much, but I have seen a filled to the neck tank down 1" after sitting overnight in a cold hangar after a hot refueling.

If your running 100LL then a leak would be very noticable with the blue stains. Not much fuel will come out of a loose cap but you would also see the stains around the cap if it did. Your caps seem a little loose if you can rotate them when there closed. I would adjust the caps a little tighter so water won't get in when it rains.

Gary
 
A 1/2 inch down from the filler neck is about a gallon and a half in my 9A. I fill them all the way up to the neck, taking the time to let it equalize, and making sure they're completely full.

And you can burn 12 in an 0320 full rich and hard, as earlier stated. I'd make sure your mixture is set correctly.
 
high fuel usage or loss

Another place you can lose fuel is from a slowly seeping/leaking quick drain valve. Sometimes a little grit will get in the valve causing a very slow leak. Easily fixed by pushing on the valve to get a good flow then letting it pop shut.
 
I have an O-320 carb 160hp with fixed pitch wood climb prop.

Fuel consumption really does depend on where the throttle is at, how high you are flying and how you are leaning.

At full throttle and full rich at anywhere from sea level to a couple of thousand feet, my RV-4 burns about 12 to 13 gallons per hour. But if I climb up to say 9,500 feet, and throttle back to say 2,300 rpm and lean it up good, I can go from IPT to EWB in under 2 hours and only burn 12.4 gallons for the entire trip.

Sounds like you "may" have a leak, but it is odd that you have seen no blue stains if your using 100 LL.

Maybe someone is siphoning a little fuel from you ? :eek:
 
12 GPH ain't right

Did someone say a 320 burns 12 GPH at full throttle? If so, I've sure as heck never seen anything close to that. 10 maybe, doing speed runs at full throttle. Normal is 6.5 to 8.5, depending on power setting.

If you lost two gallons out of a tank you didn't use on your last flight and you can't find any blue streaks, I'd suspect the vents. Dumb question, but you did say this was a new plane -- the slash on the vent is pointing forward, right?

If your O-320 is actually burning 12GPH, the first thing I'd check is mag timing. One time I tried setting the timing cold and it cost me about 2 GPH until I fixed it. When I checked it again later hot, it was probably 10 degrees retarded from normal (which is 25 degrees BTDC).
 
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jonbakerok said:
... the first thing I'd check is mag timing. One time I tried setting the timing cold and it cost me about 2 GPH until I fixed it. When I checked it again later hot, it was probably 10 degrees retarded from normal (which is 25 degrees BTDC).
Click to expand...

Could you elaborate on this? A degree or two (1 tooth) I understand but 10 degrees is about 4 teeth. Seems like a lot to me...

Chuck
 
My partner often rents from a place that always tops off fuel, apparently to the brim. One of the rules there is to catch any fuel when draining ths tanks and put it into a holding tank--something about environemntal concerns. We went there one morning as things were just getting warm and here was this line of Cessnas, all pouring fuel out of the overflows. Fuel expands more than you would think. If there was a large change in temp, consider that.

Bob Kelly
 
It was a lot!

chuck said:
Could you elaborate on this? A degree or two (1 tooth) I understand but 10 degrees is about 4 teeth. Seems like a lot to me...

Chuck
Click to expand...

I didn't count the teeth but it was almost halfway between the 25 degree mark and TDC mark on the flywheel. It surprised me too.
 
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