EGT difference.

[Lood]

I did a two hour flight back home this morning and with about 40 minutes remaining, a rise in the EGT difference got my attention. I was cruising at 9500', WOT, 50 deg ROP, 2400rpm - EGT difference is normally around 100 deg. I noticed it increasing to 120 deg and I kept my eye on it. After a while it increased some more to 130 deg. I started playing around with the mixture a little with no relevant result on the span itself so I performed a complete lean find procedure on the JPI setting the mixture at 75 deg ROP. There was no real change and after a while, the difference increased some more to 140 deg. I played around with the mixture some more and eventually set it to 100 deg ROP - again using the JPI lean find. Once again, there was no change and it rather increased to 150 deg.

During all this, the CHT's stayed put at around 310-342 deg and fuel flows were just over 9 gal at 50 deg ROP and 10 at 100 ROP. When I started my descend, the difference was 170 deg and it stayed there until I reduced power approaching the circuit. The highest EGT (cyl no 1) was between 1370-1400 deg depending on the mixture setting and the lowest EGT (cyl no 2) was at around 1260 deg. With every change in mixture setting, both no 3 and 4 cylinders' EGT were very quick and responsive, but no's 1 and 2 were rather slow and more stationary.

For the first time in the 18 odd hours flown after the last annual, the oil temp also ran about 20 deg higher than usual, but as I'm still using the stock analogue oil temp gauge, I don't worry too much about that.

Do I have reason to worry or not? I would appreciate any advice.

[KSMooniac]

First of all, running 50 ROP is not a good power setting as we've beaten to death many times here. 

Now, the EGT difference function on the JPI really serves no useful purpose.  The raw EGT values from one cylinder to another don't really tell you anything important.  It sounds like you might have an issue, but you need a better handle on the data.  Best practice with a JPI or similar is to establish your cruise setting (not at 50 ROP) and put the monitor into "normalize" mode, which will snap the EGT bars to the mid-point and more importantly, give you a better resolution on the display so you can catch small changes. 

If you see an EGT bar start to creep up or down relative to the others while in normalized mode, then you can start troubleshooting.  You might be able to see something if you do a data-dump and plot it in a spreadsheet too, even if you didn't use the normalize mode.

[Cruiser]

you don't say which one was changing (to cause the difference) ? My peak is around 1470°F so I am guessing your No. 2 was dropping in temp?  Or it was the other way (No. 1 was increasing) ? If your EGT is high, that usually means an increase of air or reduction of fuel (leaner) mixture. It might be a bad plug or intake air leak.

 If your EGT is low, that usually means less air and more fuel (richer) mixture. Intake valve or compression issues are common.

[scottfromiowa]

I have had NO issues with running 50 degrees ROP on my '66 M20E.  I agree with Bob Kromer's power settings for climb, cruise and decent as written in MAPA.  I lean aggressively on the ground and run full throttle in climb and cruise unless down low and I will keep it at 25 squared.  As long as my cylinders are running cool I don't get concerned about EGT fluctuations.  I don't understand all this 24 squared stuff and have NOT heard a good reason why people are reducing power in climb and cruise...and what is the big prejudice against 3 blade props?  I get excellent speed, climb performance and no vibration issues with my McCaulley.

[Lood]

Quote: Cruiser

you don't say which one was changing (to cause the difference) ? My peak is around 1470°F so I am guessing your No. 2 was dropping in temp?  Or it was the other way (No. 1 was increasing) ? If your EGT is high, that usually means an increase of air or reduction of fuel (leaner) mixture. It might be a bad plug or intake air leak.

 If your EGT is low, that usually means less air and more fuel (richer) mixture. Intake valve or compression issues are common.

[Earl]

Quote: scottfromiowa

I have had NO issues with running 50 degrees ROP on my '66 M20E.  I agree with Bob Kromer's power settings for climb, cruise and decent as written in MAPA.  I lean aggressively on the ground and run full throttle in climb and cruise unless down low and I will keep it at 25 squared.  As long as my cylinders are running cool I don't get concerned about EGT fluctuations.  I don't understand all this 24 squared stuff and have NOT heard a good reason why people are reducing power in climb and cruise...and what is the big prejudice against 3 blade props?  I get excellent speed, climb performance and no vibration issues with my McCaulley.

[scottfromiowa]

I have not seen these charts regarding internal cylinder pressure being highest at 50 ROP.  I'll try to check it out.  If in a turbo and not my IO360 apples to oranges on chart data.  I don't run lean of peak, but used 50 ROP as a fuel saving compromise between performance 100 ROP and fuel economy peak/LOP operation at altitude in cruise. (per Bob's article).  My fuel flow and cylinder head temps have been fine at this setting...I always fly full throttle in cruise and climb unless down low (cruise).  What I have read was temp as engine killer NOT pressure regarding TBO on engine...HMMmmmm?  Of course I back off down low because of manifold pressure extremes to 25 squared max.

[Cruiser]

look here http://www.mooneyspace.com/index.cfm?mainaction=posts&forumid=1&threadid=892#post8790

I know very little about the ICP but it just makes sense that the higher the pressure the more wear on moving parts etc. and the more severe the effect. How that relates to TBO I really am not sure. If I can get very near the same performance with less pressure and less heat it just seems to me to be a better way. Just as you are concerned about backing off the throttle down low because of maifold pressure (vacuum actually) extremes.