Tecnam P92 low oil (in yellow arc) while flying

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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c162pilot
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Joined: Fri Aug 05, 2011 2:40 pm
Location: New York - HPN

Tecnam P92 low oil (in yellow arc) while flying

Post by c162pilot »

First flight in a Tecnam P92 Eaglet yesterday as a passenger. Steam gauges vs Glass. Previously I have flown a Remos GX and understand that oil has to be a certain temperature before run up. While taxiing and run up, oil temperature gauge was in the middle of the yellow arc and went into the green arc after takeoff. However 30 minutes into the flight at 5,500 feet and with RPM's at 4,500 the oil temperature started to drop slowly into the yellow arc. Oil pressure and cylinder head temperatures remained in the green. I suggested that we return to our departure airport 18 miles away, there was an airport 2 miles away also. The temperature remained in the lower middle of the yellow arc until we switched the engine off. Any thoughts? What is the downside of running and engine with oil cooler rather than hotter?
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garbageman
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Location: Maryland (eastern shore)

Post by garbageman »

Tecnam P 92's always run on the cool side (oil temp). The green range is 90 to 110. Rotax says to keep the oil temp below 120 for most of the flight, and the oil temp must rise to at least 100 each day of flying.

At 5500ft and 4500rpm, the engine will be very cool. Thats about Va. One should cruise a Rotax at 5000rpm or so to keep the lead from messing things up. That will keep the oil temp in the proper range 85 to 100.

In winter most of us cover a part of the oil cooler or else we would not get to the 100 degree mark as Rotax requires.
roger lee
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Rotax 912ULS oil temps

Post by roger lee »

Hi Guys,

Your oil temp should be at least 120F (48.5C) before running the engine hard on the ground or taking flight. The oil temp recommended by Rotax should see 212F (100C) to burn off any water contaminants during flight. That doesn't always happen during the winter. You should be fairly close this time of year. I see 215F - 220F right now. Even 200F is okay. You should not be cruising at 4500 rpm with a Rotax 912ULS and the low rpms will also correlate to lower oil temps. You engine was not designed for that low rpm cruise. It should be 5000+ rpm and is better for cruise at 5100-5300 rpm. Technically the engine was designed to run its whole life at 5500 rpm , but most of us reduce that a little (5100-5300 in cruise) Your engine runs hotter at mid range, but also has more vibration. Your peak torque is at 5000 and as you increase the throttle the torque starts to diminish after 5000 rpm, but HP goes up. You should also be seeing at least 5500+rpm at WOT. 5550-5575 is a good place to be for the ground adjustable prop. If you are running 100LL then you should be using a lead scavenger with the fuel like Decalin and running more rpms at cruise to keep the lead blown out (i.e. 5300) Flying at low rpms, less than 5000, with 100LL will absolutely cause excessive leading over time. It will be early and unnecessary maint. If you engine rpm is higher than 5600 rpm then adding a little pitch back into the prop will help performance on the top end and raise temps a tad.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
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c162pilot
Posts: 183
Joined: Fri Aug 05, 2011 2:40 pm
Location: New York - HPN

Post by c162pilot »

The temperature gauge in the aircraft was calibrated in degrees centigrade and was over 50 at run-up and take off and did move into the green which is above 100C. So the lesson learnt here is to run the engine over 5,000 RPMs. Thank you both for your informative replies.
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