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Extreme CHT's (relatively speaking)

Atimoore

Member
Yesterday after an uneventful Superior IO-360 startup and runup, while waiting to depart all of my CHT's jumped to around 430F while idling at 1000RPM.

As I barely see 400F on even the hardest of takeoffs this got my attention and I promptly shut the engine down.

Mixture was full rich and everything else was normal apart from an infrequent (2-3 times) "thud" from the engine and fluctuation RPM's before noticing the high CHT's.

While the plane remains stuck on the ground I am at a loss trying to figure out what could of caused all CHT's to jump up.

Let me know your thoughts
 
How sudden was the jump? if it was instantaneous (like all of them moved a lot in a second), then I’d say you have an instrumentation problem.

If they all moved together but took ten or more seconds to move, perhaps your timing shifted..... what kind fo ignition?
 
The thud followed by erratic RPM is quite concerning and likely the cause or the effect. 430* at idle is WAY out of the normal range, so clearly something is wrong somewhere, assuming it is not an instrumentation issue. I would initially guess timing WAY advanced with detonation, though not sure you can get significant detonation at 1000 RPM, with no meaningfull load; It is typically seen under high load conditions. If that were the case, the thud could be pre-ignition caused by severe detonation. Detonation/ore-ignition could certainly cause fluctuating RPM at 1000 RPM. A good clue to moderate to severe detonation is a very rapid rise in CHT, relative to what you normally see. Did that happen here?

Do you have P mags? I have read several posts here about the systems auto-magically resetting the TDC point with wild timing shifts resulting.

Larry
 
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Cowl plugs?

Did you forget to remove your cowl plugs? (I've never done that! :eek:)
 
May I suggest verifying your instrumentation, as well? The following are three simple tests to verifying temperatures:

1. Do the CHTs match ambient temperature before the engine is started and out of any direct sunlight? Do they match other temperatures such as EGT or oil temp?

2. Remove the probe(s) and submerge in an ice bath (70% ice/30% water). The reading on the instrument should indicate 32°F, +/- a degree or two.

3. Similar to the ice bath test, submerge the probe(s) in boiling water and look for a temperature of 212°F, +/- a few degrees depending on elevation.
 
It would be nice, and helpful, if the OP would respond to the members trying to help.
 
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