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Uneven CHTs - real?

This is an IO-470K in a Beech Debonair.

Can this CHT variation be real? Seems very high. Also, one wouldn‘t expect number 4 to be the coolest one anyway, since it is „in the middle“.

Or is the probe possibly not wirking well? On the other hand, probes tend to either work or not, but not indicate numbers which are a bit off. Probe placement inadequate?

Frankfurt (EDFE, EDFZ), Germany

Mine on a typical flight:

The 315 is normal because it is a front cylinder.

To see a much lower temp on #4 would seem to be unusual, and yours shows a 80F max delta which does seem high. I would check probe is the same type as the others, and is properly secured. And what do the temps do as the engine cools down to ambient?

Administrator
Shoreham EGKA, United Kingdom

I didn‘t check that…

Frankfurt (EDFE, EDFZ), Germany

Over my last seven engines (four on an Aztec, three on a Navajo) I have seen much bigger variation than that.

However, the middle pair (3 & 4) have always been hottest.

If you go to an Advanced Pilot Seminar they tell you (and show you videos to prove) that much of the airflow in the engine is from rear to front, even with the cowl flaps open, which is why 1 & 2 are cool (direct incoming air flow), 5 & 6 are cool (most of the baffled air flow) but 3 & 4 are hot (airflow masked from both front and rear.)

EGKB Biggin Hill

Airflow under a cowling

Indeed, the middle ones tend to be the hottest. In some installations the back one is the hottest. And one can see big differences in the CHTs. What is really weird in this case is that the middle one is the coolest.

Administrator
Shoreham EGKA, United Kingdom

I get far bigger variations than that, although my engine is carbureted with a notoriously dodgy induction system (O-470-50). For some reason, one side of my engine runs much cooler than the other. We’ve gone through the baffling with a fine tooth comb and blocked up every possible leak we can see; it’s only 5 years old anyway.

Last Edited by Katamarino at 07 Feb 13:25
KPJC and Kent, UK

It is common on TBs to see the RH cylinders (1,3,5) hotter and I assume this is because they have the oil cooler hole behind them (behind #5) and that air escaping through the hole reduces the air pressure above these cylinders.

And this is what Bosco’s post shows.

Katamarino’s is the opposite, so I wonder what engine it is (same cylinder numbering as Lyco??) and what the baffle layout is. 284 to 357 is a massive difference.

Administrator
Shoreham EGKA, United Kingdom

I Can’t post a picture now, but will.
I’m very interested to see other ‘during flight’ displays, to understand what’s normal, accepted, acceptable and tollerated. Any combination of the above.
I don’t have the time, money or best knowledge to chase and rectify everything to give textbook values.
I have a similar display at cruise to Katamarino.
Obviously I understand that we have dozens of differing factors but it’s helpful to know what’s common, if not ‘normal’

Private strip, Essex (not mine), United Kingdom

Bosco
it could be a probe thing.. I have the same on my Arrow 200.
CHT #4 is about 20-40F lower than all others despite being the one in the back. It is because the CHT probe is piggy backed on the factory cht probe. This causes it to read slightly lower. The easiest way to identify this is to check if your CHT4 is constantly the coldest cylinder or not in all phases of a flight. If it is always showing cooler than it is most likely a probe connection related. You can also see that your EGT 4 is just fine so I bet it is the probe, especially if thats where your factory CHT probe was originally attached.

Last Edited by By9468840 at 10 Feb 12:25
EDTG, Germany, Switzerland
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