6 cylinder horizontally opposed aircraft engine.

I'm with you LB - a might strange. Not what I find - CHT definitely responds to mixture.

Cranked up the 210 the other day for YMEN. Cracked open the cowl flaps a couple of notches in the cruise to bring the CHT’s back a bit. After 5 minutes the CHT had come back about half a needle width on the gauge.

If I tweak the red knob and run the 520 at 70° LOP (using the old single probe Alcor EGT gauge, no fancy, fandangled engine monitor here), the needle moves back a full quarter scale deflection. A bit more dramatic than the half a needle width I get when fiddling with the cowl flaps.

It may just be a product of the specific engine and cowling arrangements on SWTT’s aircraft. SWTT seems know what s/he’s doing. The numbers out of the monitor are the numbers out of the monitor.

UPDATE ON CHT - disturbing!

So I flew to NSW over the weekend and closely watched by CHT on climbing out. It is the single CHT digital reader type (plus EGT). On departing Essendon last Wednesday (surface temp around early 30's), I climbed out to 3,000' initially. My CHT got to 417f. Even keeping airspeed at around 95 knots I could not keep it under this. Similar conditions continued until I leveled off at 7,500' ultimately.

On return home yesterday, in very hot conditions, I tried to climb out again at varying speeds but predominantly at 85 - 90 knots. This time I could not keep the CHT from getting up to 430f. On my second leg, climbing out it got to 417f at about 3,000' so I tried leveling off for a minute or so and the CHT dropped to 405f. When I resumed climbing it stayed pretty close to that, only going to 407f. I also climbed with slightly less than full power this time and my climb rate seemed unchanged.

Full rich for most of the climb. Leaned a little as I got above 5,000' (closer to 7+ density).

Fixed pitch 0-360 engine for clarification.

So now I'm totally bewildered. Should I level off for a minute or two when climbing to cool then engine and then resume my climb? Should I use less than full power except for initial climb out? Any advice on how to manage this so I don't stuff my engine or myself is much appreciated.

If I were you I’d first confirm the accuracy (or otherwise) of the reading.

Do you use the best ROC speed for the entire climb? I usually nose over to 120kts IAS once I’m a couple of thousand AGL.

If you're below the maximum factory / engine manufacturer recommendations, then it's really a decision for you as the owner in discussions with your trusted LAME on how best to handle your engine for longevity.

Similarly I was up on Saturday when it was 34 degrees. My hottest CHT hit 160c at 3,500ft which is my ideal maximum and my alarm is set at. I wanted to lower it so I leveled off without reducing power and nothing happened. I then backed off to cruise RPM and waited around 1 minute for it to lower and it dropped by 12deg c. I then continued climbing at full power and it didn't go up more than a few degrees. I find the CHT is all about airflow / airspeed. If you're worried about it being too high, level off, increase airspeed, reduce power and wait. If the engine isn't working as hard, the CHT's will *generally* be lower. I wonder if many pilots notice that a more coarse prop will lower CHT's for the same reason?

Maybe those smarter than I can comment on "cruise climbing" and if it's a good or a bad thing...

With respect, SWTT, the deleterious effects of heat on metal are determined by the laws of physics, not manufacturers or trusted LAMEs. If TPA’s CHTs are, in fact, regularly above around 380F, the cylinders are going to suffer correspondingly. The metal out of which cylinders are made is the metal out which cylinders are made, and the effects of heat cycles on that metal are what the effects are. Hence I would try to confirm the accuracy of the measurement, first.

I’m not sure about your point about “more coarse”. Do you mean setting a lower RPM for a CSU-equipped propellor? Lower RPM doesn’t necessarily reduce CHTs.

Cruise climb? Better cooling due to higher airspeed, better visibility over the nose and you get to the destination quicker. Unless I’m over tiger country or water, I don’t see the point of climbing at best ROC continuously to e.g. 9,500’.

Two identical engines at full power. One more coarse than the other. The CHT should be lower on the somewhat more coarse one. Within reason though, I'm not talking full fine versus full coarse. Difference in airflow, speed, rpm, fuel burn and load. It was just a minor observation.

The problem with flying in this weather is that you're so close to the manufacturers maximum OAT, plain and simple, so it's always going to show high temps, you can't help that. The best you can do is try and keep them low, knowing that high temps will of course in time do damage, but balance that with the other 10 months of the year. Hence the reason when touring why many choose to fly in the early mornings where possible, particularly up north.

Same RPM? If yes, how do you coarsen the propellor and achieve the same RPM?

A reduction in RPM can actually have the effect of increasing CHT, because it reduces thetaPPP (brings the PPP closer to TDC).

I said full power, not same RPM.

I generally use the best ROC for entire climb LB but might look to do more cruise climbing when terrain permits.

I found this in the Lycoming owners manual online. They do mention elsewhere about avoiding CHT's above 400f for prolonged periods, despite this extract saying keep it below 435f for maximum power cruise flight.

Section 3 (7)
https://www.lycoming.com/sites/defau...2060297-12.pdf

On page 3-12 it refers to maximum CHT of 500f and says
* - At Bayonet Location For maximum service life of the engine maintain cylinder head temperature
between 150°F and 400°F during continuous operation.

So do we agree that the laws of physics, Lycoming (and John Deakin at the earlier linked article) all agree that prolonged operations above 400F are ‘not good’ for cylinders?