Strange EGT and CHT

Hi Jeff,

THANK YOU so much for that explanation - That explains it beautifully and I now have a good understanding of what is happening. 

I normally do leave it it course, but as town leads me into midfield X-Wind, I went full fine, but I will do some experimentation.

I did also read on another forum that others have widened their EGT warning values for this very reason.

I also think my CHT sensors sometimes play up. I can get a high warming when on decent into the AD when backed off and trying to slow down.

John,

Back in 2014, or there about, Rotax changed the temperature probe in the heads to read the coolant temperature at the heads, not the cylinder heads themselves. The new probes go through the head into the water jacket. It's a subtle difference but requires different min-max settings on your gauges.  I have a Bristell also, and so does a friend of mine.  We think they may have been a bit behind on realizing this change. On his plane, a 2019 model with a 914, they had the limits set up for CHT, not coolant, and he overheated the engine without ever going into the red (CHT limits are higher than Coolant temp limits). Not sure what year your aircraft is, but you might review your CHT limits as these may actually be reading coolant temp at the heads, not CHT.  The old sensors measuring actual CHT are on the bottom of the cylinders and the newer Coolant sensors are on top.

Regarding your high CHT readings, remember CHT has a delay whereas EGT is almost instant.  So the CHT may have spiked as a result of a previous action.  

Hi Jeff,

Mine are on the top.  One on each side of the engine.  Mine is a 2018 912ULS.

Do you know what the values should be?  Otherwise I should be easily able to find them.

Rotax calls out the maximum coolant temperature as 248 deg F (120 C) for conventional coolant. However that is the “coolant exit temperature” (as Rotax calls it) which is a bit too late! You could ask Bristell where they set the yellow and red zones, but I would want red to start about 8-10 deg F before 248, and the yellow at least 10 deg F before that.  So maybe yellow starts at 230 F and red at 240 F.    

Ok.  I will have a look.  I am pretty sure my CTs red starts at 120, and yes, I think the readings I get are not real, as they react within seconds, which I dare say is not possible.