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I have a Rotax 912 engine, with adjustable prop. The engine is about 4 years since new, about 1500hrs.

I was climbing out(prop full rpm, engine dropped back a little from full power) with my CFI on a check ride and about 1500ft agl(1600ft msl) with outside temp around 80f the CHT began to rise near 260f, the oil temp was following it by about 20f or so. I have a 253F coolant temp sensor and it did not go off. We level out and temps were not dropping. We did a 180 back to the airport cutting throttle back increasing airspeed to 110kts or so did not cool it appreciably. Cutting to idle, gliding back upon landing the temps had lowered. Went back to the hangar to check coolant level, etc. Everything looked good. Did a couple of laps in the pattern(up to 800agl) and similar symptoms persisted. At this point it had Evans waterless coolant, the coolant was flush and 50/50 replaced it as per mechanics recommendation.

Another day, temperature inversion 75f or so on the ground 90f at 1500agl. Climbing out at around 1800ft agl CHT to about 255, Coolant light goes on and oil temps around 240f or so. Leveled off and turned around again, cooled down on power-off approach. Did a couple of laps around the pattern, at around 700agl, it would heat up. I have been climbing out 75kts when I would like to be around 65kts. Straight and level flight at 90kts did not lower the temps

One person got out of the plane to lower weight, and tests repeated with similar issues. Performance is fine and can climb pretty much at book before beginning to overheat. I am sure temps would continue to rise if power wasn't cut and would rise much faster if climbed at Vx.

Fresh gas, Sport plus oil, sensors checked out, new plugs 30hrs ago, Radiators looks clean/fins straight, all cylinder heads approx same temperature when cowling removed. Engine runs and idles as other 912 I have flown.

Mechanic is not a Rotax expert and is out of ideas and there are no Rotax specialists at the field.

Thanks
  • Re: 912 overheat suggestions

    by » 4 years ago


    Was any maint. done on the engine prior to this? Evans carries a 20-30F heat penalty so that was good that it was replaced.

    With that many hours and the increase in coolant temp and with some of the other checks done I would pull the radiator and have it flushed.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: 912 overheat suggestions

    by » 4 years ago


    Roger thanks for your reply,

    Looking over the logs, no major maintenance done, beside all the required. 200hr/annual for airframe done 30hrs ago 78/80 all around. It had it's annual done this winter and is the first time flying in warm weather since.

    Plugs looked a little on the lean side to me but mechanic said no problem.

    I'll have him change/flush the fluid and the radiator again.

    It had it's annual done this winter and is the first time flying in warm weather since.

    Thanks again.

  • Re: 912 overheat suggestions

    by » 4 years ago


    I mean professionally flushed and cleaned and not just drained. Reducing prop pitch and angle of attack can help to.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: 912 overheat suggestions

    by » 3 years ago


    Roger,

    I have been using Evans coolant since 2012 and have come close to overheating a few times. The extra 20-30 degrees will probably help me with this marginal situation.

    Three years ago in post # 7231 you has indicated the steps you use to flush water in preparation for Evans. I was wondering if those same procedures could be used to flush Evans (minus the adding of Evans Prep).

    Could I use that procedure to switch to water coolant, and is there anything extra I would need to do to remove all of the Evans ?

    Thanks, Jim

  • Re: 912 overheat suggestions

    by » 3 years ago


    Hi James,
    My bet is switching back to a 50/50 coolant and dropping those extra 20F - 30F degrees in extra heat retention with Evans will work well for you.
    A couple ways to dump your old coolant. You can use the screw on the back side of the water pump if you like. Most times I can't get to that. What I do find fast and efficient will sound goofy, but it works like a charm. I slide back the lower hose on the coolant radiator with a pan under it and let it drain for a couple seconds. Then I keep the pan there and pop the top off the black expansion tank on top of the engine and allow more coolant out.
    Here comes the fun part. :) LOL
    I toss a rag over the radiator tube and hose while they are still disconnected. Then I just cup my hand around the expansion tank and blow hard down through the expansion tank's mouth. I blow hard 4-5 times. This removes all the coolant in the system. If you have a thermostat you may have to remove another hose to drain that short section. If there is no thermostat your cooling system will be practically free off all coolant. When I do a 5 year hose change I have to remove the coolant or it would make a major mess all over the floor. This method clears the entire system. If you fail to place a rag over the coolant radiator tube and hose you will blow coolant all over when you blow down through the system. It is an open system throughout. It vacates coolant in all hoses and areas.
    I know this may sound like an odd way to drain the coolant, but it is fast and effective.
    Then just add your 50/50 back to the engine.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

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