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Thread: Oil Cooler Thermostat

  1. #1
    Birdseyeview's Avatar
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    Default Oil Cooler Thermostat

    I have an oil cooler and I've installed an oil cooler thermostat on my 912 ULS. The thermostat opens at 180-190 F. The normal oil temp operating range in the Rotax operating manual is 190-230 F. I've only got 85 hours on the engine to date and I've noted that the engine oil temp usually operates at close to 180 after warm up, with up to 200 during operation at hot ambient temp. I've read that to eliminate moisture from the engine oil, to prevent internal engine corrosion over time, that the engine oil should be operated at temps above 200 F. Should I be looking for a replacement thermostat with a higher temp setting? Is there a concensis on the best thermostat to buy and what its operating temp set point should be? I appreciate any informed opinions based on your experience and judgement. The following is a picture of the cheap thermostat I bought from Kitfox a few years back and I'm assuming that its temp set point is fixed and can't be altered. There are no oil thermostats in the current Kitfox parts catalog.

    Image.jpeg
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  2. #2
    Senior Member
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    Default Re: Oil Cooler Thermostat

    What does under your oil cap look like after flying? My experience is engines that don't get warm nough have moisture under the oil cap.
    Dustin Dickerson

    Building 7ss STI x 2
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  3. #3
    Senior Member jrevens's Avatar
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    Default Re: Oil Cooler Thermostat

    Quite a few of us run that same t-stat. The thermostatic element is easily replaceable, but I contacted the supplier and they informed me that a higher temperature version isn’t available. I haven’t pursued it any further at this time. I think the unit is still useful in that it helps to get the oil temp up to the minimum necessary for run-up and full power running conditions quicker.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
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  4. #4
    Senior Member Dusty's Avatar
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    Default Re: Oil Cooler Thermostat

    Quote Originally Posted by Shadowrider View Post
    What does under your oil cap look like after flying? My experience is engines that don't get warm nough have moisture under the oil cap.
    Moisture won't stay in the systym even at the slightly lower than recommended oil temps.
    I haven't seen evidence of corrosion in an engine that is flown, only in an engine that was regularly ground run (way too cool)
    Moisture under the cap is the best indicater of a problem looking for a solution.
    If it's dry after a normal flight don't stress over it

  5. #5
    Birdseyeview's Avatar
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    Default Re: Oil Cooler Thermostat

    I've never noted any moisture under my oil tank cap, which is a good sign. Also, I just recently discovered that the oil temp sensor on the 912 series is very near the oil pump which is located at the coolest temp of the entire oil circuit so that temp is what's showing up on my panel. The hottest oil is in the oil tank and I read that it can be significantly higher than what is being read on my panel, even with an oil cooler in place and doing its job well. As a result, I'm thinking that the hot oil in the tank is typically high enough to boil off any moisture during a normal flight and that moisture will escape through the oil tank vent. With all that being understood, along with my dry oil cap, I was probably in good shape all along and just didn't understand the oil circuit well enough. So, thanks guys for all the good tips because they spurred me on to investigate this oil circuit enough the discover what's really going on in there.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  6. #6
    Senior Member jiott's Avatar
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    Default Re: Oil Cooler Thermostat

    Right on Larry, in fact the oil running thru the engine is even hotter than what's in the tank.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  7. #7
    patrick.hvac's Avatar
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    Default Re: Oil Cooler Thermostat

    I used this one instead. Same one Mike Patey uses. It can be purchased with higher set temperatures.
    https://www.improvedracing.com/high-...ductsearchusen
    🇨🇦CANADA
    Flying | SS7 | G3X | Edge 912

  8. #8
    Senior Member jrevens's Avatar
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    Default Re: Oil Cooler Thermostat

    Quote Originally Posted by patrick.hvac View Post
    I used this one instead. Same one Mike Patey uses. It can be purchased with higher set temperatures.
    https://www.improvedracing.com/high-...ductsearchusen
    That looks real nice, Patrick... I'm considering changing over to one of those.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  9. #9
    Super Moderator Av8r3400's Avatar
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    Default Re: Oil Cooler Thermostat

    In my perspective, I have never liked putting this many connections on the suction side of the oil pump. Too many places to leak air into the system.

    I have a cover over my oil cooler that I install in cold weather to keep the temp up and remove it in warmer weather. I understand this would be more difficult with the oil cooler mounted piggy-back to the radiator on the newer planes.
    Av8r3400
    Kitfox Model IV
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  10. #10
    Senior Member
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    Default Re: Oil Cooler Thermostat

    Do yourself a favor and throw the T-stat in the garbage can.

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