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Oil temperature control and thermostat temperature selection for Rotax 912, what a daunting task! There seems to be more confusion and opinions here than should be the case. Rotax is remiss for not giving us more guidance for such an important topic.

Following is from official Rotax information.

The following is from the Rotax 912 Operators Manual:
• The oil temperature sensor for reading of the oil inlet temperature is located on the oil pump housing.
• Oil Temperature:
  • o max 285° F
  • o min 120° F
  • o normal operating temperature 190-230° F
Warming up period …. Until oil temperature reaches 120° F
• Avoid operation below normal operation oil temperature (190-230° F) as possible formation of condensation water in the lubrication system badly influences the oil quality.
• To avoid possible accumulated condensation water, at least once a day 212° F must be reached.

And the following is from Rotax SL-912-012 Use of an Oil Thermostat for Rotax Engine Type 912 and 914 (Series):
• If the aircraft manufacturer of owner thinks that the oil temperature is too low during engine operation, an external oil thermostat can be installed.
• Opening temperature must be between 82° C and 90° C (180-194° F)

Discussion: My maximum and cruise oil temps (measured at the low temp point where Rotax put the thermocouple) with a Perma-cool thermostat and the stock 180° F wax stat is under 180° F in autumn air temps. How seriously should we take the requirement to “at least once a day 212° F must be reached”? How seriously should we take the “avoid operation below normal operation oil temperature (190-230° F)? Right now (cool fall air) I do not meet either criteria, best I can tell. Given that Rotax draws our attention to the fact that we are measuring the temperature at the coolest point in the oil’s journey, does this mean we need to add a thermocouple to the engine outlet or tank inlet to see if we are reaching 212° F. Has anyone done this? Ideally it seems we want the oil at some point to reach 212° F. Plus we need to know if at the engine oil pump inlet it is within operating limits. Do we add additional complexity to the oil’s travel to raise the temperature to 212° F if that is not happening? Or is this simply a requirement that we take with a grain of salt and keep flying.

Here is what I am thinking. I am planning to raise the Perma-cool temperature by replacing the 180° F wax stat with a 195° F, as well as measure the temperature coming into the oil tank with temporary instrumentation. I think my inlet temperatures are way too low this time of year. I am speculating that even with the 195° F, I will not come anywhere near 200° F, let alone the recommended 212° F in cool weather.

Obviously there are some high time 912s out there doing fine. What are you guys seeing in the way of oil temps?
Any ideas? Help?

Dennis
  • Re: Acceptable Oil Temperatures/how to achieve them

    by » 10 years ago


    The normal temp range of 190F to 230F is a good target range. The 212F mark is so hopefully you will burn off any impurities like moisture in the oil. It is harder this time of year as weather cools to keep temps up, but that's fairly simple to do. You can use that 195F thermostat if you would like. You need to make sure both oil and coolant are up in temp. What many do is take a piece of 2" wide aluminum tape (no duct tape because the glue makes a mess) and place it over the top 2" of the coolant radiator and oil cooler. I live in Arizona and a 2" wide tape makes my temps in the winter about 200F-215F for the oil and CHT's.
    The colder the weather, like living in Montana or some other really cold place, may need to add another strip of tape. I leave my 2" wide tape on all winter.

    You can block off the coolers in 1" or 2" swaths.

    If you have a flight down around 180F no problem, but try to keep them up if possible above 200F.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Acceptable Oil Temperatures/how to achieve them

    by » 10 years ago


    Thanks for the help Roger. My Cessna Lycoming engine had similar winterization techniques. I just thought that with Rotax being a modern design, and liquids flowing, we could do all this automatically. I will tape over the cooler after I try a different thermostat or two. And thanks, I will use metal tape, not duct tape if I do this.

    This weekend I plan to replace the 180 Permacool wax stat with either a 195 or a 205 (I know 205 is not what the Rotax SI recommends) – or I may end up trying both. The thought here is that if the oil temp were over the max thermostat temp, it would make no differences which of those were installed. In other words, if I have 210 oil temps, there could be either a 195 or 205 and either would be fully forcing all oil through the cooler. This merely controls the minimum, not the maximum temps. Now I need to decide which is better, 195 or 205 going into the engine. The thought here is that, at least in winter, I will never see oil temps higher than the wax stat, so do I want 195 or 205 going into the engine. I will also try a slow speed max power climb to see how hot the oil gets after it stabilizes. In summer I do see higher oil temps than 205. But again, a lower thermostat should not change those high readings.

    I already installed a 195 Thermo-Bob coolant thermostat, which works very well in these cool temperatures. Even if I go to idle and perform a long descent, the temps remain 195. Before installing it, I flew the same day, and coolant temps never got above 180, identical to oil temps at that time. I only have an hour on the Thermo-Bob, but I have not seen temps above or below the thermostat setting after warmup. And warmup does occur much faster. Note that warmup on oil temps did NOT seem faster with the Perma-Cool. Although I am satisfied with the Thermo-Bob results, I will need to see how this works in hot temperatures. The full-time 3/8” bypass might raise temperatures beyond acceptable in summer. I am thinking this will not be the case because even now my temps are well within limits. But we’ll see. I will post my results.

    BTW, I am flying a Rans S-7 Courier with an 80hp 912 out of Shippensburg Airport (N42) in PA.

    Dennis

  • Re: Acceptable Oil Temperatures/how to achieve them

    by » 10 years ago


    Today air temps were quite warm, 50 degrees. Flying today before doing anything, the oil temps stabilized around 180 degrees in cruise, 190 in climb. When I looking inside the “180 degree” Permacool I found it had a 170 degree wax stat. So I installed a 195 degree wax stat of equal dimensions. Flying again in the same 50 degree air, cruise oil temps were 200 degrees, and in climb they were about 210. I am not sure how this will work out in much cooler or much warmer air temperatures, but I will find out. Also, I wonder what the actual highest temperatures might be before the cooler (which would be when the oil enters the thermostat). I don’t want to break down the oil with overly high temps given that we are measuring with a sensor mounted at the lowest temperature point in the system.

    I never did install the 205 wax stat for a couple reasons. The main reason is because I am not smart enough to know when I can deviate from a manufactures instruction; and Rotax says 180 – 194 degrees. The other reason is because a 195 is already 25 degrees hotter than the 170 that came with the stock Permacool.

    Roger is probably right, I should have taped metal tape over the heat exchanger and been done with it. Fortunately this was very easy to do.

    Dennis

  • Re: Acceptable Oil Temperatures/how to achieve them

    by » 10 years ago


    Denis where did you get the 195 and 205 wax sats from??

    Mike G

  • Re: Acceptable Oil Temperatures/how to achieve them

    by » 10 years ago


    Any auto parts store, but you will need to take the Permacool pellet with you. It is just an automotive pellet. The Permacool wax stat pellet is easily removable by simply removing the c-clip. However, the c-clip is easily lost as it springs out of you hand and across the hangar. It took me an hour to locate mine, so be careful. In the auto store, ask to look at coolant thermostats (behind the counter) and match up the pellet that comes out of the Permacool for dimensions. I used a Stant 14789, 195 degree. It was not an exact match, but I determined it would work, and it seems that it did. I would like to know the exact replacement, and if I find out, I will post it. Just use metal cutters to take the pellet out of the metal housing.

    I would be interested in knowing what you end up doing.

    Dennis

    Thank you said by: Keith Moon

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