Temperature issues

[hubcap]

Recently got Myrtle back after annual, upgrading the panel. I immediately noticed that my #2 cylinder EGT was running cooler than the other cylinders. I have GAMI injectors and run LOP most of the time in cruise. The CHT seemed to be consistent with the other cylinders but I was very interested in discovering why the EGT was low. The injectors had been pulled during the annual due to some other work that was performed. I was concerned that the injector had gotten some obstruction. I sent GAMI the engine info from my last flight but they recommended doing a full GAMI Lean test and then send them the data.

I decided to have my mechanic replace the lead (just in case) this week and flew this morning. I was so happy to see #2 running at the same temps as the other EGT’s. I did 2 complete lean tests at different MP’s. It was just the lead. The one that was bad did not look burned, but it was reading ~200 degrees cooler than the new probe. 
 

[0TreeLemur]

Drat, you figured it out already.   That was going to be my guess.   CHT is the indicator of power production, and a single lower than normal EGT in a cylinder that is making normal power just doesn't make sense in a fuel injected engine.  Glad you figured it out.

[skykrawler]

Yet another engine problem that turned out to be incorrect indications.

 

[kortopates]

Drat, you figured it out already.   That was going to be my guess.   CHT is the indicator of power production, and a single lower than normal EGT in a cylinder that is making normal power just doesn't make sense in a fuel injected engine.  Glad you figured it out.

Actually, CHT is a very poor proxy for power production. EGT is a much better one but is better at telling us about mixture than power.


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[0TreeLemur]

1 hour ago, kortopates said:

Actually, CHT is a very poor proxy for power production. EGT is a much better one but is better at telling us about mixture than power.


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I agree Paul.  My statement lacked specificity because both mixture and cowl flap setting and cooling air distribution are confounding effects. 

However, I was thinking more of detecting changes from experience.  Consider the particular case of cruising flight in an engine with good baffles and a reasonably well balanced cooling air flow distribution.  In this case an unusual deviation of CHT would indicate a power deviation in a cylinder, wouldn't it? 

In our J, all engine monitor data since 2020 indicate that #2 CHT consistently runs about 20F cooler than the others in cruise after leaning.  CHTs 1, 3, and 4 are typically within about 5F of each other.   According to the JPI EDM900, cyl #2 is not the leanest or richest when I lean it out LOP.   It seems to me that  that this difference results from cooling effects.   If I ever see a deviation from that, I'll be suspicious of some change in power production. 

Does this make sense?

 

[kortopates]

I agree Paul.  My statement lacked specificity because both mixture and cowl flap setting and cooling air distribution are confounding effects. 
However, I was thinking more of detecting changes from experience.  Consider the particular case of cruising flight in an engine with good baffles and a reasonably well balanced cooling air flow distribution.  In this case an unusual deviation of CHT would indicate a power deviation in a cylinder, wouldn't it? 
In our J, all engine monitor data since 2020 indicate that #2 CHT consistently runs about 20F cooler than the others in cruise after leaning.  CHTs 1, 3, and 4 are typically within about 5F of each other.   According to the JPI EDM900, cyl #2 is not the leanest or richest when I lean it out LOP.   It seems to me that  that this difference results from cooling effects.   If I ever see a deviation from that, I'll be suspicious of some change in power production. 
Does this make sense?
 

Absolutely, knowing your historical data makes a world of difference.

For in flight cruise monitoring your best defense to be alerted to change is to use Normalize mode. That will at least normalize all the EGTs and with newer EDM firmware CHTs also. This will highlight any deviation from “normal” while flying. Of course with any power change you’ll have to re-normalize it.


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