Does your 912ULS really use only 1/2 litre (500 ml), or 1/2 US quart of oil per
50 flying hours? Mine has done a total of 780 hours ( 560 since a rebuild at
220 hours, following a crash involving a previous owner ) and the oil
consumption
has steadily increased.
Every 50 hours I replace the oil filter with the Rotax supplied type and the oil
is the recommended Aeroshell SPORT Plus 4. The instantaneous compression test
done recently gives about 3% difference, highest 177psi to lowest 172psi, and
aircraft climb performance remains strong at each annual permit renewal flight
test. I won't do the scary leak-down compression test again, having once nearly
broken my hand when the propeller kicked.
Researching on line tells me that the maximum acceptable consumption is 60 ml
per
flying hour, or 3 litres (3 US quarts) for 50 flying hours, while mine currently
averages 40 ml / hour, or 2 litres / 50 hours. It grieves me when others
tell that they hardly ever top up their oil tanks.
Oil pressure in flight is just over 4 bar or 60 psi. Oil temperature in the
cruise
varies seasonally between 80 and 100 deg C ( 176 and 212 deg F ). Living this
far north means that most of the year it's at the cooler end.
The inside of the exhaust outlet tube is no more sooty than other people's
engines
with lower oil consumption. There's no "wet" oiliness evident in the exhaust,
but a slight brown exhaust stain extends rearwards under the port wing and
along the fuselage.
Last year the four inlet valve stem seals were replaced, but that didn't help
either.
Also when I borrowed a "cheap" not very clear boroscope, I couldn't see
signs of scratching on the cylinder walls.
I'm starting to suspect that a few Rotax 912ULS owners may be deceiving
themselves,
although those I know locally definitely aren't.
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