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Rotax 914 Sensors


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My 2007 Sting S3 912 ULS had the then typical single CHT and single EGT probes.  The engine was rock solid and, to be honest, I never analyzed the data from my Dynon EMS.   Not the case with my Cirrus for the last 6 years.  All cylinders have CHT and EGT which, admittedly, makes sense for fuel injected engine.  I analyzed my data for trends, performance tweaks and troubleshooting.  I discovered a broken plug and clogged FIs before they were problems.  I also used the data to tune performance. Now coming back to the fold, planes I see generally are single CHT and EGT.

Is there any advantage to having 2-4 CHT sensors (depending on engine vintage) and 4 EGT?  Or does it not really add anything for a carbureted Rotax 914?

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For me the advantage is for diagnostics. As an A&P it makes it a little easier. As a pilot it tells me if any changes in normal operation occur in flight before they become a larger issue. I came out of HPN one night in a C- 340 and noticed high EGT on one cylinder with no other indications. When I landed inspection showed I had a valve problem and had to replace the cylinder.

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14 hours ago, Warmi said:

I did install 4 EGT sensors on my S4 but only 2 CHTS - my understanding is that for water cooled cylinders there is no advantage monitoring all 4 CHTs..

I think this is what I’ll do.

I read this on Rotax-owner so i guess if I have an ‘older’ engine multiple CHT’s might make sense it’s actually measure the heads.  If ‘newer’ (this was written 2 years ago, so approximately 2017 or later) then CHT is essentially measuring fluid temp so not much sense is measuring all four. 


It depends on the age of your engine, or at least the age of your heads.
The early heads had the temperature sensor mounted on the BOTTOM of the heads and measured the temperature of the head's metal.
About 5 years ago, the newer, Rev.1 heads changed to measuring the coolant within the head and the sensor mounting location was moved to the TOP of the head.

If your temp sensors are on the TOP of the cylinders, you are measuring Coolant Temps. Bottom = CHT, Top = COOLANT

While it makes sense to measure all 4 EGTs,  The coolant circulation is common to all 4 heads and the temps will be nearly the same in each.
If One cylinder went 'Cold', the hot coolant from the other 3 heads would heat up the Dead Head to match.
One(1) COOLANT Temp Sensor is Enough.  #4 usually runs 'Slightly' hotter than the other 3.

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