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RV-12 CHT and EGT split question

Bob Kuykendall

Bob Kuykendall

Well Known Member
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I just took delivery of a used RV-12 and I'm still figuring it out.

While I was flying it to its new home, I noticed that there was a noticeable split between the EGTs and CHTs for the right and left side. Both were in limits, but right side was a bunch cooler than the left.

Is this what happens when the carbs are out of sync? Or is it likely caused by something else?

Advice and guidance welcome.
 
The Coolant Temps (aka CHTs) should be very close together since they are in the same water bath that is being circulated by the water pump. I wonder if they are calibrated to read the same. Consider doing a hot water bath test and see if they give about the same reading when immersed together in boiling water.

The EGT's are much less coupled, and it's not unusual for them to be as much as 100 F away from each other (IIRC, I don't have any logs in my laptop at the moment.). I added EGT's for my forward cylinders and now have 4 values that don't agree with each other. :)

If there's a significant and consistent difference, then perhaps a Carb Guru can give advice for trying to determine if one side is too rich/lean compared to the other and how to address such, but that is magic that is beyond my spell book.

BTW, the best resource for engine management and diagnostics is Mike Busch's site -- Savvy Aviation. They let you upload your engine data and do your own analysis for free. They don't do analysis for you on Rotax engines, but you can teach yourself a lot by reviewing your flights. If you have Dynon avionics, the only file you should upload is the one that ends with ___USER_LOG_DATA.csv.
 
Thanks, everybody!

I flew again today for about an hour, and the CHT temps and EGT temps were very close.

The only change was that I re-mounted the oil cooler in its proper location. Earlier, the bottom edge was aft of the locating spools, and not engaged with them as it ought to have been, and that left a bit of a gap for air to leak through. I guess the last person to put the bottom cowl on was in a bit of a hurry. Anyway, I'm hard pressed to see how that would affect the balance of either CHT or EGT, so its still a bit of a mystery.
 
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