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Hi, all --

I was assured at some point in ancient history that the CHT sensors on our 2015 912ULS, SN 6784449, were the same as the oil temp sensor, but upon inspection I just can't convince myself of that.  I reviewed the IM 72-00-00 Figs 2 & 3 on pg 3 (2015-01) and confirm that ours point off to the side at 30ish degrees.  They are bolt heads on rings and do not have a tab sticking out.  They also contact coolant.  Am I insane, or are these in fact "new style" and therefore useless to cannibalize for oil temp troubleshooting?

We have a SkyReach BushCat with two Sertrab 10-vane (50-110-7612) coolers.  In general, the BushCat tends to be overcooled; metal tape across the top cooler is standard in cold weather.  [SkyReach has not yet approved a thermostat, much to our dismay.]  She's never given us a problem in the Georgia, USA summers even a bit past 100F.  Water usually runs 190-200F and oil flirts with the 220s, and I have our temp alarm set for 230F to start paying attention.  [We also thought that 250F is redline; I must have misread that since it's 285F and we see discussion of running at 250F happily.]

Last year we (Laura and I are both LSR-Ms for airplane, and we maintain our S-LSA planes) did the 5-year rubber swap, which was the first time to our knowledge the oil system was completely drained after the SkyReach build fill.  Everything was awesome all last typical hot summer, though, as well as through the winter.  Then, suddenly, we hit hot oil temps.

We run [93 octane no-Ethanol] MoGas and suspect that we still had winter blend in hot May temps.  Moving to 50/50 with AvGas took care of the apparent vapor lock and inability to start when hot that was also a new experience, but even straight AvGas didn't keep temps down in the most recent tests.  Between then and now we've flushed both coolers, checked all lines for kinks (all sharp turns are tube rather than hose, which is helpful), confirmed that no routing has been bumped near hot metal, ans tried various tests.  While she is a little cooler after the flushes, which we believe from the pump strain early to smooth running maybe 4-5 seconds later did appear to push out some goop, we are still warmer than in the past.  I can easily push her through the 230s with just 2k-3k feet of climb, and even in level flight at cruise RPM she eventually gets up there -- whereas previously we could climb as hard as we like, and cruise at nearly WOT for 90 minutes straight,  all summer long.  Something has changed, and we don't like not knowing :-(

Back to sensors ...  I was going to swap in a cylinder sensor to see if it's the device, but that doesn't look to be an option.  Short of ordering another, which appears to be anything from "pricy" to "OMG that's a much as gasoline these days" and also takes time, I've also seen reference to measuring resistance and want to go and read up on that (that was harder

  https://www.rotax-owner.com/en/general-tech-discussion/9285-oil-temp-sensor-resistance

than it sounded).  Beyond that, though ... any testing or troubleshooting suggestions?

TIA




  • Re: New or old CHT sensors? + hot oil checking

    by » 2 weeks ago


    Text gone crazy/gremlins.


  • Re: New or old CHT sensors? + hot oil checking

    by » 2 weeks ago


    "....flushes, which we believe from the pump strain early to smooth running maybe 4-5 seconds later ...."

    What coolant are you using? The only time I have seen a radiator flush, have the above effect, is when hard or dirty water has been used in the cooling system over an extended period OR something has come adrift internally, to cause a blockage.

    As far as I understand, the standard Rotax oil temperature sensor & coolant sensors have the same part number/are the same component..

    You can check in the Parts Catalogue;

    Oil Sensor , Chapter 79-20-00, Pages 8 & 10, Part No 965531

    Coolant Sensor Chapter 75-20-00, Pages 5 & 7, Part No 965531

    The gauges on your average light aircraft are notoriously inaccurate & prone to progressive even sudden failure.

    At the first unexpected change in a reading; cross check with allied gauges eg oil temp high, oil pressure normal - suggests a failed sensor OR gauge, low oil pressure / coolant & oil temps okay also suggests a faulty sender/gauge. n is to go with potentially cheapest "fix" - replace sensor(s).


  • Re: New or old CHT sensors? + hot oil checking

    by » 2 weeks ago


    Continued from above; 

    Standard diagnostic advise usually suggests the use of "Master Gauges" however these may be difficult to access/borrow/steal, so go with the cheapest alternatives. Start by "swapping " sensors (if wiring harness permits, just cross wires) to see if there is a change that can narrow down the fault, followed by replacing with new sensor(s). If this does not result in a better "read out" then you may have to consider replacing the gauge.


  • Re: New or old CHT sensors? + hot oil checking

    by » 2 weeks ago


    Sean, et al --

    Thanks for the replies!

    "What coolant are you using? The only time I have seen a radiator flush, have the above effect, is when hard or dirty water has been used in the cooling system over an extended period OR something has come adrift internally, to cause a blockage."

    We're running Dexcool at 50/50, although I don't know that that's relevant since we flushed both oil coolers.  When the oil was showing hottest, stepping on 250F, water did get up to 220F, but in general and even through the hot-but-not-crazy testing it's still been in the 190s.

    As soon as the first oil came out everything was basically black, so we couldn't see what was being pushed, but it sure sounded like some glop was being freed.  That did also drop the [indicated] temps a bit, which supports the theory, but we ain't out of the woods yet.

    Thanks again

     


  • Re: New or old CHT sensors? + hot oil checking

    by » 2 weeks ago


    Howdy again

    "As far as I understand, the standard Rotax oil temperature sensor & coolant sensors have the same part number/are the same component..

    You can check in the Parts Catalogue;

    Oil Sensor , Chapter 79-20-00, Pages 8 & 10, Part No 965531

    Coolant Sensor Chapter 75-20-00, Pages 5 & 7, Part No 965531"

    Well, yeah!  That's the "am I insane??" aspect.  I do see that, and my IPC is dated 2017.  So what about the Installation Manual and reference to the change?

    Attached first here is a pic of our still-connected oil temp sensor.  It's gold and has a little head for the spade connector.  It looks just like a 965531.

    BUT ... attached second and third are pictures of the loosened and then removed CHT sensor connection.  This is, as far as I can see, just a ring on a bolt.  Did I pull the right thing, or have I somehow completely failed to locate the CHT sensor port?

    Perhaps we should have been asking SkyReach what they use for CHT measurement since it sure doesn't look like a 965531 (or I'm lost as above, or I'm just insane).

    Thanks again

     

    32928_2_20220620_070959.jpg (You do not have access to download this file.)
    32928_2_20220620_070657.jpg (You do not have access to download this file.)
    32928_2_20220620_070731.jpg (You do not have access to download this file.)

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