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Thread: High CHT's and EGT's... a mystery!

  1. #1

    Join Date
    Apr 2019
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    2

    High CHT's and EGT's... a mystery!

    Hi all. Please help. 1993 Glasair II S-FT with a Lycoming IO-360B1A, now with about 850SMOH. Bendix mag on the left, Lightspeed electronic ignition on the right. Always run at about 40-50 degrees rich of peak for smoothness, decent fuel flow. Not flown regularly, esp during winter. About 2 years ago, started noticing EGT's and CHT's climbing slowly. They were always similar for many years... 1380's and 380's all across. Nowadays, CHT's are all in the low 400's (with #4 between 415 and 425), and EGT's are about 1400. Recently, had my JPI ED monitor go bonkers, as one cylinder went above 500, followed by another one. After checking all connections, sent the unit back to JPI, and they found that the MUX board needed replacement.. cant complain after 15 years of uninterrupted use!). Reinstalled, and temps all still all in the low 1400's and 400's. This is a change after so many years, which I'm not comfortable with. They say it's unlikely to be the probes.

    So, here we go... replaced the fuel servo with a new Precision unit (last check was 2002!!). O/H'd the divider. Cleaned all GAMIjectors. Magneto and Lightspeed are at spec with timing. All new plugs top and bottom. Then on to reaming the exhaust valve guides... #4 had some gunk, but the rest were in remarkably good shape. Removed exhaust stacks and replaced two flange gaskets... two had mild leaks). Removed all 4 intakes, and replaced with new gaskets and hoses. Went up for a ride today, and ughhh..... temps still the same.. low 1400's and low 400-420 CHT's. Yes, I can dial in more fuel flow (it was always happy at 10.2-10.3gph), but now it needs 10.7 to just start bringing down temps.

    Is checking the cam lobes/lifters next? Could this be spalling? And would it affect every cylinder?

    My mechanics are baffled. Is this maybe a rusty camshaft that is tired of midwest winters and humid summers? And would that be a cause of slowly rising temps?

    Any thoughts/comments/suggestions/ideas would be welcomed and appreciated. Thanks!

  2. #2
    FlyingRon's Avatar
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    Aug 2011
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    NC26 (Catawba, NC)
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    For CHT issues, I'd always check the baffling before anything else. Doesn't take much of a gap in that to really raise the temps.

  3. #3

    Join Date
    Apr 2019
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    Quote Originally Posted by FlyingRon View Post
    For CHT issues, I'd always check the baffling before anything else. Doesn't take much of a gap in that to really raise the temps.
    Baffling in good shape... no obstructions.

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