CHT settings - EVERYONE PAY ATTENTION

[DBRV10]

Folks, having just responded to a thread on oil temps, I realised this is a genuine serious thing, but nothing at all as important as CHT.

Now if you have a Rotax....or liquid cooled heads you need to think carefully about different parameters. Jabiru heads, the numbers should be a lot lower also.

But the bulk are Lycoming and TCM I would imagine.

CHT should be set green up to 380F, yellow from 380 to 400, and 400 and above in RED with alarm set for 400 or more.

And if anyone wants to debate this WITHOUT thinking with their brain first, they will get a fair dose of "keyboard lashing" from me.

Just think about for a while ....I know someone is going to be tempted to say 450 or 500F

If you cant climb and cruise under 380 F there is a baffling problem, or you have a good dose of detonation going on, and if you do not, you are not far from creating some if you are not careful.

This thread should be posted as a STICKY for all to read.

 

[mmarien]

Interesting comments. From a Lycoming Key Operations Flyer:

http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key Operations.pdf

Minimum in-flight CHT should be 150[ch730] F (65[ch730] C), and maximum in most direct-drive normally aspirated Lycoming engines is 500[ch730] F (260[ch730] C). Some of our higher-powered more complex engines have a maximum limit of 475[ch730] F (245[ch730] C). Although these are minimum and maximum limits, the pilot should operate his or her engine at more reasonable temperatures in order to achieve the expected overhaul life of the power plant. In our many years of building engines, the engines have benefited during continuous operation by keeping CHT below 400[ch730] F in order to achieve best life and wear of the power plant. In general, it would be normal during all-year operations, in climb and cruise to see head temperatures in the range of 350[ch730] F to 435[ch730] F.

Personally my top yellow is 210C - 225C which is within Lycoming recommendations. You'll find articles showing that at high tempuratures the strength of aluminum deteriorates. Good reason to keep your CHT within reason. Your experience?

 

[DBRV10]

Many of the Lycoming publications contradict each other, or over time they do depending on the political forces at play at the time.

The one you quote here does make a very good point about keeping your CHT below 400F.

Folk who really know engines, probably better than TCM and Lycoming do these days, prefer 380 as a YELLOW limit, and 400 or so the redline as it were, and as you point out the material strength changes as temp gets over 380-400.

So, I did ask for lots of thinking first. Setting a CHT alarm at say 435 or 450 might be well and good during a cruise. But what you do not want, is an alarm set too high when you have a normal of sub 380, and lets say you have a pre-ignition event, the CHT climbs rapidly and you have very little time to deal with it. So setting your alarm limit right up the top end does not give you long from the alarm going off to Ohh No!!!

You are going to have sub 380 in the climb and sub 250 in the cruise if you have a good setup, so 380-400 is ideal for a Yellow warning, and redline ALARM at 400.

A preignition event can destroy a cylinder in as little as 60 seconds, give yourself a fighting chance. Ohh and do not drop spark plugs and keep them!