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  #1  
Old 11-24-2021, 08:00 AM
design4p design4p is offline
 
Join Date: Jul 2018
Location: CORWEN
Posts: 64
Default Erratic CHT on Cylinder 2 Lycoming 390

Hello,

Now 43 hours from new - last flight the CHT on Cylinder 2 of my Lycoming 390 performed erratically whilst the other 3 CHT were as normal at around 340 Fahrenheit (170 degrees C). Number 2 cylinder moved very quickly between 340 and 410 Fahrenheit (170 and 210 degrees C) and then returning back to normal.

I tried various settings flying LOP and full rich but the erratic CHT on cylinder 2 continued.

Any suggestions of the cause would be most welcome.

John
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  #2  
Old 11-24-2021, 11:06 AM
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DanH DanH is offline
 
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Location: 08A
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Quote:
Originally Posted by design4p View Post
Number 2 cylinder moved very quickly between 340 and 410 Fahrenheit (170 and 210 degrees C) and then returning back to normal.
The cylinder has thermal mass, so "very quickly" suggests an instrumentation issue. How quick was it?
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  #3  
Old 11-24-2021, 11:16 AM
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airguy airguy is offline
 
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Location: Garden City, Tx
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Quickly is relative - if it was a matter of seconds, that's instrumentation. If it was a matter of minutes, then it has a possibility of being real.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 900 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #4  
Old 11-24-2021, 11:18 AM
RV10Pilot RV10Pilot is offline
 
Join Date: Jan 2005
Location: Medford, NJ USA
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If the engine feels the same as before the erratic readings, I agree with Dan and it is most likely an instrument problem. I would trouble shoot in the following sequence. Check the egt probe connections. Replace the crimps. Check the probe. Replace the probe. Somewhere in the sequence I would check where the wire connects to the engine monitor. With only 40 hours, my best guess would be an electrical connection issue.
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  #5  
Old 11-25-2021, 03:13 AM
design4p design4p is offline
 
Join Date: Jul 2018
Location: CORWEN
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Hi,

Thanks for the replies - All good information - I will check as suggested.

Great support this Vansairforce forum.

John
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  #6  
Old 11-25-2021, 03:35 AM
Avanza Avanza is offline
 
Join Date: Jul 2020
Location: Vastervik Sweden
Posts: 88
Smile EGT

If EGT was stable on all cylinders during the event, chances are that it is a
poor crimp or a bad probe.
CHT is slower to react than the EGT if something happens.

Good luck
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