O-360-A4M - egt/cht question

moonshine

moonshine

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Hi all

Last couple of long(ish) xc flights at 75% peak egt (or as close as carb'd engine gets to it) at 7-8k feet I've noticed that the number 4 cyl is somewhat hotter than the rest of the bunch and the EGT on it is somewhat cooler than the bunch.

Fairly representative picture -

EGT 1 - 1562
EGT 2 - 1527
EGT 3 - 1533
EGT 4 - 1501

CHT 1 - 369
CHT 2 - 366
CHT 3 - 365
CHT 4 - 390

Thoughts?
 
moonshine said:
Hi all

Last couple of long(ish) xc flights at 75% peak egt (or as close as carb'd engine gets to it) at 7-8k feet I've noticed that the number 4 cyl is somewhat hotter than the rest of the bunch and the EGT on it is somewhat cooler than the bunch.

Fairly representative picture -

EGT 1 - 1562
EGT 2 - 1527
EGT 3 - 1533
EGT 4 - 1501

CHT 1 - 369
CHT 2 - 366
CHT 3 - 365
CHT 4 - 390

Thoughts?
Click to expand...


EGT 1 - 1562
EGT 2 - 1527
EGT 3 - 1533
EGT 4 - 1501

Holy crap...:hairraise::yikes::eek:
 
moonshine said:
Hi all

Last couple of long(ish) xc flights at 75% peak egt (or as close as carb'd engine gets to it) at 7-8k feet I've noticed that the number 4 cyl is somewhat hotter than the rest of the bunch and the EGT on it is somewhat cooler than the bunch.

Fairly representative picture -

EGT 1 - 1562
EGT 2 - 1527
EGT 3 - 1533
EGT 4 - 1501

CHT 1 - 369
CHT 2 - 366
CHT 3 - 365
CHT 4 - 390

Thoughts?
Click to expand...
Absolute EGTs mean practically nothing. You need to determine how far each cylinder's EGT is from the peak for that cylinder. You might also try enrichening the mixture a half gph and see if the #4 CHT drops.
 
gismo said:
Absolute EGTs mean practically nothing. You need to determine how far each cylinder's EGT is from the peak for that cylinder. You might also try enrichening the mixture a half gph and see if the #4 CHT drops.
Click to expand...

Wanna bet.:yesnod::yesnod:..

Here is what 1775f for 3 minutes does to a piston that ran at 1700f for 300 hours perfectly safe.... ' disclaimer.... this is a water cooled motor'.. Don't try this with an air cooled motor:no::nonod:..

Look at the Lyc limits.... I thing MAX EGT's are in the high 1400 range for a naturally aspirited stuff..
 

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gismo said:
Absolute EGTs mean practically nothing. You need to determine how far each cylinder's EGT is from the peak for that cylinder. You might also try enrichening the mixture a half gph and see if the #4 CHT drops.
Click to expand...

1 is at peak, 2 and 3 30ROP, 4 60ROP
again, that's about as close as it gets to the lean side of things on the engine - and I'm content with all of it but the CHT 4

Another common occurance - bank imbalance at "just shy of WOT" at those altitudes. I'd love to just stick it to WOT and sit happy at 8000+ (that's what, about 75% at ISA+15), but with the PowerFlow I'll just bust through the RPM redline :dunno:

Example of bank imbalance

EGT 1 1591
EGT 2 1518
EGT 3 1584
EGT 4 1489

CHT 1 364
CHT 2 370
CHT 3 362
CHT 4 383
 
N801BH said:
Wanna bet.:yesnod::yesnod:..

...
Look at the Lyc limits.... I thing MAX EGT's are in the high 1400 range for a naturally aspirited stuff..
Click to expand...

How do you suggest finding the peak egt on the naturally aspirated stuff then if it's somewhere from low 1500s to low 1600s depending on the day, mood, alt, temp, humidity etc on a O-360? ;)
 
moonshine said:
How do you suggest finding the peak egt on the naturally aspirated stuff then if it's somewhere from low 1500s to low 1600s depending on the day, mood, alt, temp, humidity etc on a O-360? ;)
Click to expand...


I will buy high 1500's to low 1600's on a TIT reading.. An EGT number that high ....:hairraise::yikes::eek:...

I am assuming this is an experimental?:dunno:
 
Last edited:
N801BH said:
.
Hmmmm........
What does the Diamond POH say for EGT numbers???
Click to expand...

Not a word*. CHT arcs are 150-475F 476-500F 500+F
you get the idea

*On running lean it mentiones doing that at or below 75% power and says to pull the mix until the engine starts running rough, then ease it back a bit to smooth, at the same time the EGTs should reach the max reading. Tada.
 
moonshine said:
1 is at peak, 2 and 3 30ROP, 4 60ROP


CHT 1 364
CHT 2 370
CHT 3 362
CHT 4 383
Click to expand...


All those numbers are completely normal. CHT#4 will be highest because it is running closer to max power EGT than the rest.

All the numbers are WELL within Lycoming limits. I don't see what you think is a problem???
 
moonshine said:
Hi all

Last couple of long(ish) xc flights at 75% peak egt (or as close as carb'd engine gets to it) at 7-8k feet I've noticed that the number 4 cyl is somewhat hotter than the rest of the bunch and the EGT on it is somewhat cooler than the bunch.

Fairly representative picture -

EGT 1 - 1562
EGT 2 - 1527
EGT 3 - 1533
EGT 4 - 1501

CHT 1 - 369
CHT 2 - 366
CHT 3 - 365
CHT 4 - 390

Thoughts?
Click to expand...

Everything looks great except that the CHT on #4 is a wee bit higher than the other 3, but still well within the published acceptable limits. EGTs are fine, ignore the Chevy pilot.

Check the aluminum straps that wrap around the #4 cylinder to see that the gap at 6 o'clock is the same as the strap gap on the other cylinders. 1 to 1.5 inches is normal, though I've not seen this dimension published anywhere. Make sure that the device which holds the baffle straps to the cylinder is in place (some aircraft use springs, some use safety wire, some use threaded rod.)

Also check to see if there excess casting flash around the cooling fins, especially in the area between the intake and exhaust valves. It's not uncommon to find on Lycoming cylinders and can restrict cooling airflow.
 
moonshine said:
Hi all

Last couple of long(ish) xc flights at 75% peak egt (or as close as carb'd engine gets to it) at 7-8k feet I've noticed that the number 4 cyl is somewhat hotter than the rest of the bunch and the EGT on it is somewhat cooler than the bunch.

Fairly representative picture -

EGT 1 - 1562
EGT 2 - 1527
EGT 3 - 1533
EGT 4 - 1501

CHT 1 - 369
CHT 2 - 366
CHT 3 - 365
CHT 4 - 390

Thoughts?
Click to expand...

You've got a 61 degree spread on your EGT's, which is excellent for a carburetor engine. EGTs are fine.

CHTs also look great, but I don't really like running higher than 380 at cruise. You'll certainly want to check the baffles around the #4, but I think as kgruber suggests, if all other things are equal (probe types and locations on the exhaust pipes) you're more rich of peak on the #4, making more power, resulting in a higher CHT.
 
kgruber said:
All those numbers are completely normal. CHT#4 will be highest because it is running closer to max power EGT than the rest.

All the numbers are WELL within Lycoming limits. I don't see what you think is a problem???
Click to expand...
Ditto. And ditto also on the comment about the insignificance of absolute EGT values. For more on this, see the Lycoming Key Reprints articles on engine operation.
 
Last edited:
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