I bought a 260B that has been hangared with full tanks for the last 10 years. The fuel is basically 10 years old. It looks (blue, no water) and smells good. The engine has been overhauled, seatbelts are being installed, and annual should be completed within a week. I'd hate to discard $450 worth of fuel. On the other hand, I don't want to damage my engine or worse, make an emergency power off landing. I've read that fuel that's 1-2 years old should be OK, but what about 10 year old fuel? Does anyone have any experience or scientific data to tell me if the fuel should be safe to fly with?
Thank you

Joachim - only have experiential data and logic. There are two metal tanks on my Twin that are rarely used but I try to keep a gallon in them to keep seals happy. I notice that as the fuel evaporates over time in the vent lines, a gooey substance forms - not in the tanks but out the vents. From a logic view, the chemical composition will have likely changed somewhat due to evaporation. On the other hand - have personally used older fuel than that from SEALED containers when overseas without difficulty. However, another pilot had a different experience with old fuel overseas - it caused the engine to fail and a forced landing. She handled it well and all parties were uninjured. The aircraft was repaired and is flying again.

If it were me, I'd dump the fuel, change the bladders (they likely leak at the top) and all fuel and fluid carrying hoses so that the newly overhauled engine is not immediately contaminated with old hose debris. That is just an opinion ... and perhaps you've done all that already.

As a general rule avgas is much more stable than car gas and thus does not deteriorate nearly as quickly. I have seen 6 year old fuel fly just fine in a 250 Comanche. It's a tricky question because I feel as you do about wasting the fuel and where to dispose of it. I do not believe it would damage the engine, but it's a risky question.

Joachim,

In my unscientific opinion, $450 worth of new gas is cheap compared to the possible alternative outcomes. I would not replace the bladders unless the usual symptoms appeared. I would replace all the hoses as they are probably stiff and maybe even original.

Pat D.

You're buying an airplane and worried about the cost of the fuel in it? Sell it to a drag racer and fill your Comanche with new fresh fuel.

Clarence

After more thought if it were mine, I'd drain one main tank into clean gas cans. Fill that main with fresh fuel and use that tank for takeoff and landing. Use old fuel at altitude only. If runs well on old fuel I'd use the gas can fuel to fill all tanks but the one main tank used for takeoff and landing. And yes I think $450 worth of fuel is significant.

A reasonable suggest LeWayne.

I like the idea of one main tank with new fuel and testing the old fuel at altitude.
Thanks a lot for everyone's input and discussion.

Just read an old Lycoming article that said a senior Shell engineer indicated 100 octane kept in sealed drums was good for 5 years. The same fuel stored underground with occasional use was good for two years. Beyond that time, a gum substance develops that sticks to the carburetor and fuel injectors -- which means rough running and some loss of power.

Pat D

I wanted to report back:
The fuel performed well. No rough running, etc.

Great! Hope you are enjoying your New to You Comanche