The Rotax oil temperature sensor is located at the oil pump, which sees
oil that has just returned from the oil cooler. We measured the
temperature of the hot oil as it entered the reservoir during a flight
yesterday, and found it to be consistently 48 degrees F hotter than the
standard sensor in cruise (5.3 gallons per hour, 912S). This dropped to
40 degrees at lower power. Both temperatures were measured with the
same instrument, using type K thermocouples, so I believe the difference
is accurate.
During a Rotax forum at Arlington, Phil Lockwood stated that the oil
temperature should not exceed 220 degrees, which is much lower than the
limit published by Rotax. Perhaps the difference we measured between
hot and cool oil explains his conservative limit, but I assume that
Rotax bases its recommendation on the location of the sensor they
provide. Does anyone know more about this?
We have a baffle in the cooling duct to direct most of the incoming air
through the coolant radiator, which has only about 1cm of overlap with
the oil cooler in our installation. The part of the duct feeding the
oil cooler is only about 2cm high, though oil temperatures were also
satisfactory with only a 1cm opening. (We saw two other Europas,
including a demonstrator from Lakeland, with similar baffles at fly-ins
this summer, so this modification seems to be popular.) Our summertime
oil temperatures peak out around 220 in the climb, and stay well below
200 in cruise, so we were a bit worried that the oil won't get hot
enough to clear out the water when the OAT is 50 to 60 degrees cooler in
the winter. Now it looks as if indicated temperarures of 140 to 150 in
the cruise may be adequate.
Dave DeFord
N135TD
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