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Old 06-03-2022, 09:43 AM
rvator10 rvator10 is offline
Join Date: Apr 2006
Location: Fountain Hills, arizona
Posts: 160
Default Excessive CHT - Help

Hello and sorry if this topic has already been discussed,
I have a new build -7A with a new Lycoming XIO-360 engine and snorkel inlet.
My first flight (5 minutes) the CHT's hit 550F and I quicky landed.
It was a cool 70F morning and test altitude was 1400-3500 ft.
All the baffling (new)appears perfect with little to no leaking.
I'm just staring my investigation and my first question is (did you install the lower cowling louvers?)
I did not, and that's my starting point for correction.
All suggestions are welcome
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Old 06-03-2022, 09:51 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,828

What ignition, set at what timing?

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Old 06-03-2022, 10:03 AM
jcarne's Avatar
jcarne jcarne is offline
Join Date: Jul 2016
Location: Worland, Wyoming
Posts: 2,327

Do you have a larger picture, am I gathering that all of your CHT's went above 500?

I currently have my cowling louvers taped off and honestly I don't know that they really do much for cooling as my temps are still very normal. Hasn't been super hot out yet though.
Jereme Carne
RV-7A Flying as of 03/2021
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Old 06-03-2022, 10:32 AM
keitht keitht is offline
Join Date: Jun 2016
Location: coupeville wa
Posts: 239
Default CHT overtemp

The chart you posted is really hard to see the individual data but it does appear to be a very serious CHT overtemp if the sensors are reporting correctly. You might want to give Mike Busch at Savvy Aviation a call for his expert advice. At a minimum would recommend boroscoping all cylinders looking for piston, valve and bore condition. I would drain oil and send it out for analysis and go from there depending on results. You may get away without a complete teardown.
I would not consider even running the engine until you have those tasks done.
There are a number of factors that could cause high CHTs, ignition timing, lean mixture, high power at low airspeed, leaking baffling etc. An RV-7(A) with one occupant light fuel load and a (I)O360 can climb out quite respectably on 24inches of MP and 2400 RPM at 120 knots with a new engine to keep the CHTs below 420 so keeping the speed up and the power down is all goodness with a new engine. The fuel flow should be 16+ gph at full rich under those conditions.
Its good that you have data recorded to aid in the analysis and determination of best course of action going forward.

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Old 06-03-2022, 10:44 AM
KeithO KeithO is online now
Join Date: Jul 2010
Location: Jackson,MI
Posts: 56

Could you post the raw data in a text file ?

First of all, have you validated the signal levels by placing one of the thermocouples in boiling water and in a glass with ice cubes ? These 2 points should tell you if the system is properly calibrated.

What is the blue signal curve that starts out much lower ?
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Old 06-03-2022, 10:53 AM
BH1166 BH1166 is offline
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 754
Default Do Not

Cut your cowl and add louvers Ö.. removing air isnít your issue, they really donít do much in my experience/opinion.

If new engine, has it been broken in using factory protocols?
RV6A Purchased N72TX
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Old 06-03-2022, 11:01 AM
rvator10 rvator10 is offline
Join Date: Apr 2006
Location: Fountain Hills, arizona
Posts: 160
Default lots of Q&A

I don't suspect instrumentation error, there are 10 thermocouples that read within 5F in a nominal condition, during operation the egt, oat and oil temp all read normal values, but can perform the ice/hot water testing. all other temps seem to be in line, oil 200, egt 1200, oat 70.
the lower line on the chart is % power, see y axis RHS.
the file attach feature looks like it will only handle pictures not Excell files, so help...
the new engine test run log had 1 hr 20 min and at 2700 rpm 425ish CHT.
I haven't verified the timing yet (both are magnetos) and should be 25 BTDC.
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Old 06-03-2022, 11:12 AM
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Ironflight Ironflight is offline
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 13,156

Getting to 550 that quickly….I have to echo the thoughts to check timing - in all my years of running these engines, that is what seems to quickly create very high temps most quickly. And it is so easy to think you have it right when in fact, it is way off.
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
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Old 06-03-2022, 11:32 AM
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Jpm757 Jpm757 is offline
Join Date: May 2013
Location: Sherman, CT
Posts: 1,071

I agree with Paul that timing is likley the issue. My new IO-360 M1B was shipped with the mag timing 3 to 4 degrees advanced. I would recommend checking mag timing on all new factory engines before first startup.
RV6 #20477 completed 1991 sold.
RV7 #72018 N767T first flight 11/21/2017
(KOXC)Oxford, CT, (0NY0)North Creek, NY.
1941 J3 Cub skis, floats.
Current Project Javron Super Cub
Thank You Doug!
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Old 06-03-2022, 11:34 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,472

I would be looking at instrumentation anomolies. 550 in a couple minutes is insanely high. I don't see how too much advance could drive temps that high. You can only advance so much and then power and temps fall off. Can't read your chart, so that limits my thoughts. If no instrument errors, next guess would be detonation. That WILL drive up temps very fast. Detonation can occur at full power with too much advance. Detonation causes a VERY rapid rise in CHTs. Again, can't read chart to assess.

You sure you select the correct thermocouple type in the EIS? Some systems, such as G3X, allow both types for CHT and if set wrong, can read in the ballpark at low temps and way off at high temps.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 06-03-2022 at 11:45 AM.
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