Exhaust gas temp vs. ambiant temp

tawood

tawood

En-Route
Joined
Sep 22, 2015
Messages
2,558
Location
SE Michigan
Display Name
Display name:
Tim
Hi all,
The aircraft I bought this spring is the first aircraft I've ever had with an exhaust gas temp gauge (one cylinder only, but better than nothing I guess): Cherokee with O-320.
I thought I had a pretty good handle on using it for leaning, but lately, now that I'm flying with hot outside air temps, I'm not so sure...
I expected that the exhaust gas temp shouldn't change much regardless of the OAT, but now I think I'm wrong, or else maybe my gauge is wrong...I am seeing peak lean temps waaaaay (75F +) hotter with the OAT at 90F, than with the outside air temp at 50F. Is this normal?
 
Absolutely. The air-fuel mixture is different, so it burns differently, so energy output is different. Plus, the energy change changes the temperature of the output air... 50F air +200F is different than 75F+200, but the +200 may be +250 due to a leaner mixture out of the gate. So long as your EGT isn't enough to melt steel, you should be okay ;-)

Of course my numbers above are arbitrary and round.
 
Not so much a change because of the OAT....but density which affects the air fuel ratio. The higher density altitudes should cause your engine to run richer and possibly a few degrees cooler in the EGT.
 
Last edited:
Higher air density makes the engine run leaner.

EGT isn't an important absolute value. It's just a trend indicator. You don't lean to a number, you lean to a value relative to peak.
 
Stewartb said:
Higher air density makes the engine run leaner.

EGT isn't an important absolute value. It's just a trend indicator. You don't lean to a number, you lean to a value relative to peak.
Click to expand...
So....you don't need to lean when you climb? :D
 
Checkout_my_Six said:
Not so much a change because of the OAT....but density which affects the air fuel ratio. The higher density altitudes should cause your engine to run richer and possibly a few degrees cooler in the EGT.
Click to expand...
Then why am I seeing the opposite? Higher DA is showing HIGHER EGT...and isn't peak just peak? I would assume peak would be the same ratio and thus the same temp...
 
Air is warmer coming in the engine, and doing less cooling around the engine.
Are you running the same manifold pressure?
Yes, lower density air will run richer if you don't move the red knob. But, you moved the red knob.
 
Stewartb said:
Yes, that proves the point.
Click to expand...
Your earlier comment :
"Higher air density makes the engine run leaner,"
is incorrect. As the density altitude goes up, the mixture becomes richer, hence the need to lean at altitude.
 
As density altitude increases air density decreases. Simple stuff.
 
If you lean it, and EGT gets cooler, that means that cylinder is lean of peak.
 
Witmo said:
Your earlier comment :
"Higher air density makes the engine run leaner,"
is incorrect. As the density altitude goes up, the mixture becomes richer, hence the need to lean at altitude.
Click to expand...

Ummmm, no.
 
I think I misunderstood the terms being used. I'm used to using the term "density altitude" not "air density." As density altitude goes up air density goes down. My mistake. I need to be more careful.
 
Ya but .....what about once you leveled off? :D

Btw...I had lunch with Tim and his lovely bride last Saturday....I bet his pony tail rivals yours. :)
 
Last edited:
Checkout_my_Six said:
Ya but .....what about once you leveled off? :D

Btw...I had lunch with Tim and his lovely bride last Saturday....I bet his pony tail rivals yours. :)
Click to expand...

Once I level off I can (and do) lean out, sure.

I didn't realize Tim joined the long-haired cult. Since he didn't have one last time I saw him (and it's been a long while since you last witnessed my ponytail first hand), I still bet that I win the award for "Longest haired hippie." :)
 
You must log in or register to reply here.
Back
Top