Low CHT but High EGT

[JCD]

Wondering what suggestions I can get on this. A little back ground first.

'78 M20J 201

IO-360 ~1500 hours SMHO

fly ROP per POH

cylinder #3 plug fowled out a week ago (see picture) all new plugs and now I am seeing Cylinder 3 EGT highest and CHT lowest (see pictures) in all phases of flight. 

 Oil consumption, maybe a quart every 6-8 hours and all oil analysis come back with excellent results.

I am thinking bad injector and going to Gami. Thoughts and comments much appreciated. 

Edited June 19, 2016 by JCD
Added pictures

[JCD]

Jim

I am an aerospace engineer for 20+years but only a 150 hour pilot. Got my license 11 months ago. So I am pretty conservative when it comes to deviating from the POH on a 1500 hour, 21 year old engine. I would like to get a few more years out of her before I have to overhaul it. 

I have tried leaning it out but it starts running rough at the setting in the picture at 9.4 GPH at 5500 ft MSL. I chicken out and go back to POH settings. 

Even with all that said, it still doesn't explain the EGT/CHT difference on one cylinder 

Edited June 19, 2016 by JCD

[kortopates]

Looking at the picture it looks like you may have excessive oil leakage in your cylinder so you might want to pull that plug after a short interval of time just to see how its doing.

Looking at your engine monitor data recognize your highest EGT on #3 is by no means a high outlier; not at 8-11F above the other 3.

With those caveats above, if you want to check the health of your mixture distribution system (i.e. Gami spread) and ignition system I highly suggest you run our Savvy test profile, download the data and then upload it to SavvyAnalysis.Com and you can follow our write-up for how to interpret the data here: https://www.savvyanalysis.com/articles/in-flight-diagnostics (its all free) I am saying this because looking at a point in time temperatures does absolutely nothing to separate ignition issues from mixture issues. One really needs the independent test to make any conclusive findings.  Before you run the test profile though I suggest you set your EDM monitor sampling interval to ~2 second data sampling rate from the default of 6 if not done already. If by chance you get a mixture spread of worse than 0.5 GPH, don't give up right away but clean the injectors and try again. Its unlikely your Lyc IO-360 will need Gami's to achieve 0.5 GPH or better but they do help. But I would recommend not purchasing them till the testing shows you need them.

If you you find it runs rough as you lean it out, at the very least the test profile is going to show which cylinder, at what degree LOP what is the roughness from. 

However, if you want to run it conservatively at 60% power that is fine. But realize that is a low enough power setting that it doesn't matter where you leave the mixture. You can run it at peak safely at 60% if temps remain low, and if not run it above or below peak just enough to keep the CHTs below 380F which looks like is not going to be an issue for you. Once you go above 60% you'll want to run it sufficiently LOP or ROP in cruise to keep it out of the red box: https://www.jpinstruments.com/wp-content/uploads/2013/05/Mike-Bush-Red-BoxRed-Fin.pdf 

One last caveat though - don't trust your engine monitor though to tell you what is 60% power; especially LOP. Use the simple formula to do so manually (e.g. GPH*appropriate-multiplier/total HP= %power;for you 14.9 should be the multiplier)

That should help you get going.

 

Edited June 19, 2016 by kortopates

[mooneyflyfast]

Your egt and cht's are normal. Your egt difference is is very small. Mine runs around 100 degrees.  Absolute egt temps. are not important anyway.

 I'm guessing  the left plug (the one with oil on it) in the picture is the bottom one.   You may have an oil control ring problem--especially since fine wire plugs are more resistant to oil fouling,  I wouldn't worry about it unless the plugs continue to foul out on that cylinder.  Then you might want to top that one cylinder. I had this same problem on my previous engine with similar time in service. 

[JCD]

51 minutes ago, bluehighwayflyer said:

Mine is at 1850 hours and I pay no attention whatsoever to the POH's recommended settings.  Some of them are fine but others will do anything but insure long engine life.  Formal education notwithstanding, much can be learned about combustion theory and aircraft piston engine operation by reading John Deakin's columns, which I have linked below for reference.  The short version is that 40 dF ROP is where internal cylinder pressures, which we approximate by reading CHTs, are the highest and 80 dF ROP is max power.  So leaning away from 40 dF in either direction will lower your internal cylinder pressures and CHTs and in so doing be kind to your engine.  Most folks, including whoever configured your engine monitor, use 380 dF as a max CHT for long engine life.  Below 60 or 65 percent power internal cylinder pressures are low enough that you can run even at 40 dF ROP if you want to without hurting anything, so how you handle the mixture becomes much less critical.

That having been said, EGT "spread' doesn't mean much of anything whether ROP or LOP, and yours looks fine to me regardless. Your lower CHT on #3 could indeed be caused by a mismatched injector, but that's not the only possible cause.  You could try swapping its injector with the #4 injector to see what affect that has.  

When all four cylinders are LOP you can calculate percentage of power strictly from fuel flow.  No need to consult the POH.  The formula is derived from compression ratio and for our engine you multiply your fuel flow by 15 (14.9 actually, but 15 is close enough and is easier to work with) to dermine how many horsepower you are producing.  So at 8 GPH you are making 120 horsepower, which is 60% of our max rated 200 horsepower. I find the JPI percentage of power algorithms not to be all that accurate LOP and this formula to be more reliable, but perhaps yours will be different.

I hope I didn't offend you, but they just don't teach you this stuff when you are getting your PPL and at least one other prominent member here who is also an aeronautical engineer sings Deakins' and his company, Advanced Pilot Seminars', praises pretty loudly whenever he gets the chance.

Jim

http://www.avweb.com/news/pelican/182544-1.html

http://www.advancedpilot.com/tech.html

Thanks for spreading the knowledge here.  I went to the advanced pilot link and went through the Setting your mixture brief.  Wow!  I just learned a lot!!!  I am going to try this.  This is not what I was taught to do but it make perfect sense.  I live in Phoenix High DA is a way of life.  Setting the mixture this way should help a lot in my take off and climb performance.  Thanks again!!!

[N201MKTurbo]

You can't compare #3 to the other cylinders. #3 is where the factory gauges are so the EGT and CHT sensors are different for that cylinder. Unless you have removed the factory gauges and are using the scanner as primary indications and you are sure all the sensors are installed the same. 

On aanother note if your EGTs are high and your CHTs are low your timing may be retarded.

[Browncbr1]

5 degrees retarded resulted in very low.. Extremely low chts and about 100 degree higher egts for me.   Check to make sure your timing is 25DBTDC on both mags and soak your injectors in hopps.    Start running LOP below 70% power and you'll be happy.   IMHO 

[aaronk25]

Wondering what suggestions I can get on this. A little back ground first.

'78 M20J 201

IO-360 ~1500 hours SMHO

fly ROP per POH

cylinder #3 plug fowled out a week ago (see picture) all new plugs and now I am seeing Cylinder 3 EGT highest and CHT lowest (see pictures) in all phases of flight. 

 Oil consumption, maybe a quart every 6-8 hours and all oil analysis come back with excellent results.

I am thinking bad injector and going to Gami. Thoughts and comments much appreciated. 

Also for what it's worth some mechanics set the timing at 20d BTDC instead of 25, because the 25 is a rarely used now. This was done on my J and speed decreased 7kts and egt when's up 60-75f. Mpg went down.

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