Engine Operating Tips/Rich or Lean of Peak

[Bob Cook]

Richard

Perhaps the following might help. My oil stays clean for 20-25 hrs and then I change at 25-30 hrs. Plugs go for 100 hrs. Leaning is critical to maintaining clean engines.

1) lean, lean, and lean..... on the ground. MAX EGT or until the engines are about to quit.

2) Lean on descent. Keep engine temps up.

3) Do NOT lean on climb!

4) lean ROP or LOP to >60 ROP if necessary... depending on power.

5) Never start the engines unless you are going to fly.

6) never fly for less than 1 hr.

7) do NOT run at low power settings (<50%) for any length of time unless you lean to peak EGT! PEAK EGT!

8) Do not idle the engines for any length of time. I get my clearances and ATIS with a handheld.

9) Keep up your temps by keeping cowl flaps closed except on climb. Try and keep them up to 190 deg (oil temp).

10) Insulate rear oil tube to keep condensation down on rear engine.

If you adhere to the above rules you will NOT have any problems. I have followed these rules for many years flying Cessna products and it does make a difference..

Fresh oil is cheaper than new engines. Leaning saves fuel and eliminates carbon.

Bob

[Ernie Martin]

Been in my little Bahamas island with essentially no Internet for 3 weeks. Saw Bob's posting about LEAN, LEAN, LEAN and had two thoughts:

A. Sorry that GMAS no longer contributes, but glad he didn't see Bob's posting or we wouldn't hear the end of it.

B. Although I agree completely with most of what he says, I do NOT recommend departing from your POH. My two Skymasters (a 337D and a 337G) warned against operating lean of peak, at peak EGT or within 50 degrees rich of peak. I follow that advice and operate about 75 degrees ROP at cruise; my plugs are clean as a whistle.

So I would change Bob's point 4 to read "Lean to 60-75 degrees ROP as soon as you get to cruise" and point 6 to "Do NOT run at low power settings (<50%) for any length of time", and I would then follow all these points religiously.

Ernie

[Bob Cook]

Ernie

I didn't say lean ROP, I said "lean ROP or LOP to >60 ROP if necessary... depending on power".

Your POH shows max cruise settings and they are at PEAK EGT if you compare the fuel flows with the published TCM figures in the 360 manual.

"Depending on power" is the key phrase.

I do not advocate running LOP....... that is up to the skill, and knowlege of the pilot. Some pilots run LOP above the shoulders......

bob

[OSCARDEUCE]

My POH says lean to max then enrichen 2-3 units on the EGT.
1968 O2-A. The combat vets who flew O2-A's in combat swore by this. Good enough for them over the bad guys, good enough for me.
Tom

[Ernie Martin]

Bob:

Sorry if I misunderstood. I don't know what it means when you say "lean ROP or LOP to >60 ROP if necessary... depending on power". Perhaps you can clarify. But my 2 POHs were clear: at cruise run only 2+ divisions (or over 50 degrees) rich of peak EGT. No ifs ands or buts. Just like Tom (OSCARDEUCE) says. Your point 4 (although unclear) suggests something different. And your point 7 is different.

BTW, I'm not saying that it is technically unwise to operate as your points 4 and 7 indicate. I think that there is enough data out there showing that at low power settings it's hard to damage the engine by operating close to peak EGT or even lean of peak EGT. It's just that you're likely to have any warranty claim nullified by departing from the POH and that the POH recommendations (2+ divisions rich of peak EGT) leads to good combustion results (i.e., clean plugs).

Finally, kudos to Kevin for removing this topic from the old thread and starting a new one.

Ernie

[Bob Cook]

Ernie

ROP = rich of peak
LOP = lean of peak.
< = less
>= more


Compare the TCM power / fuel specs and then compare the POH and note where the POH compares with fuel flows...........

The manufacurers are either trying to sell fuel economy or speed which are at opposite ends of the power spectrum.

re 4
I am not advocating or suggesting either way.

Re 7

You cannot hurt the engines at low power settings as pre-ignition
only occurs at higher power settings, however, condensation increases, oil temp decreases, cht decreases, and carbon deposits increase.

I know how I like to run my engines and I am not about to tell anyone how to run theirs.


Bob

[skymaster]

hey bob: what is your TIT number at lean. mine is 1440. J

[Bob Cook]

I really do not pay much or any attention to the TIT unless it hits 1500 + and that is only when I go thru the leaning process.

The TIT goes up with unburned fuel being burned in the exhaust and tends to go down with leaning and equalize close to the rear cyl EGT temp.

1440 - 1450 thereabouts seems to be about right. I am very concerned about front engine oil temps.. Can't get the temp up past 170 no matter what I do. Other than tape any ideas? I have looked at the thermovain but seems to be okay.

Bob

[Ernie Martin]

Bob:

I considered not replying, so it doesn't look like we're arguing, but I thought that the topic is too important to leave unclear. And also, maybe we'll add a little spice to the Board.

1. I'm still NOT clear of what you mean when you say "lean ROP or LOP to >60 ROP if necessary... depending on power". You know that I'm an engineer, so I know what ROP, LOP, > and < mean. I had hoped you would expand a little, since to me leaning to "LOP to >60 ROP" suggests operation anywhere between LOP to over 60 degrees ROP, and much of that range is specifically prohibited by the POH.

2. I don't doubt that the Cessna values for max cruise performance published in the POH may be based on peak EGT operation (probably to make the airplane look good on paper), but that same POH specifically prohibits cruise operation at peak EGT or any leaner than 50 degrees ROP.

3. Finally, I wanted to clear these things because your initial answer seemed to be suggestions for Richard on how to operate his bird, not a listing on how you operate your plane (notice the use of the word "you" instead of "I" in points 5, 7 and 9). And you end by saying "if you adhere to the above rules you will not have any problems".

Bottom line is that I think all of your guidelines are very important, and should be followed closely by all Skymaster operators, except for one: at cruise, don't operate LOP, or between peak EGT and 50 degrees ROP -- instead, operate where the POH says, namely between 50 degrees ROP and 75 degrees ROP.

Where do you stand on this point? You are probably the most savvy operator of Skymasters on this Board. I'm sure that other operators -- including average users -- would like to know.

Ernie Martin

[Bob Cook]

Ernie

Wonder why no one else has jumped in ?

There are a number of factors as to how you manage or treat your engines;

1) experience
2) type of 337
3) mission or profile
4) wx
5) instrumentation........ etc. that affect or that should influence the way you manage the engines.

Simple....run full rich.
Easiest....... >ROP. Safest either/or.

Consider the POH...
Written by the manufacturer for "dummies". It would be yellow and black if written today "Engine management for dummies". Cessna did not design the engines... they are OEM and operating or performance specs should be published by TCM and NOT Cessna. It is based on the instrumentation and influenced by the profile of the 337 owner.

All that said the engines and INTSTRUMENTATION is 40 - 90 yrs old depending on the initial design. The original designers of the IO-360 aren't even around. If you have a JPI, Shaden etc. there is no reason you cannot go beyond the bounds set out in the POH as long as you understand the rules and play by the game. Somewhat more complex when dealing with turbo charged engines due to cyl temps, pressures and intake temps.

Preignition or detonation can destroy an engine in seconds if you are not carefull. Closer to Peak at higher power levels increase your chances of damaging your engine if you are not monitor the engine performance and react quickly. A lack of maintenance increases the risk as well including the unskilled or newbie pilot.

Sooooooooo.
Each case is different. Having proper knowlege and being able to monitor the engines (flying the ac has a higher priority) you can "tweak" the engines to obtain the desired affect.. ie. lower fuel consumption, less carbon, or higher oil temps.... even longer life.

As I said each case is different.
I do run LOP at cruise if I need to stretch a run and I do lean to keep the unburned fuel to a minimum. If I am in the middle of a IFR flight I may just run rich and not worry about the engines.

I DO NOT run between Peak and 60 ROP !!!!
I do run at peak using lower power settings and LOP during cruise at 65% power when I consider it worthwhile. I never run less than 65% power at any time even on most of my long descents. It is important to keep up the oil temps and keep condensation to a minimum.

I won't say how long I have been flying cessna products....
but I can say that I would never go beyond the POH unless I did have some form of advanced instrumentation that I can TRUST. The guages in the 337 is like measuring wind with a wet finger. The "economizer" guage in the 337 is RELATIVE TIT or last cyl EGT and does not represent what other cylinders are doing.. A FALSE POSITIVE indication things are doing fine while the engine can be destroying itself.

now you have my opinion which has not changed since day one. None of this applies to those running around the berry patch on a sunday afternoon. In this case you just need to make sure you have lots of fuel to keep the fires lit.

Wouldn't it be nice to have a Honda VTEC engine with turbos and then you would be totally bored and this thread would not exist.


Bob

[Ernie Martin]

Thanks, Bob. Your answer covers all bases, so it's of help to the broad range of readers of the Board: those whithout advanced instrumentation (and the expertise to use it) should "never go beyond the POH", and the more knowledgeable ones with the advanced instrumentation can go beyond the POH in the ways you suggest.

Ernie

[JMH]

Sorry to resurrect an old thread, but I’m trying to find the best techniques for an O-2A… have a edm-760 twin installed, that lists individual temps for the cylinders.

Question#1- how should I use the individual CHT knowledge? Since it is not in the manual (using the 1985 1L-2A-1 as the POH), one instructor told me 400deg is the limit, but I cant really verify that anywhere. Should that take precedent over the typical Cylinder temp gauge which only goes up to 238, where 190 is the optimum temp? Not only for a “limit” but also for leaning and cowl flap ops… leaning on the ground will increase those CHTs, so it concerns me getting close to 400 (because of that IPs comments)

Note for #9 below, that should be 190 cylinder temp, not oil…?

Question #2- for a “normal” climb the book says to pull both RPM and HG pressure “in to the green arc” and fly 105-120 KIAS with 14gph to 5000’ decreasing to 12gph at 8000’ and 10gph at 12000’… how should I be attaining those gph? I would have assumed by leaning, but #3 below seems to counter that. Leave it at 2600 rpm, full rich and modulate throttle? There is a caution about leaning “below placard values” (@2800RPM) so it almost implies that we should lean TO those values.

I have a similar question for cruise, but I see if there is already thread for it that covers it… thanks!


1) lean, lean, and lean..... on the ground. MAX EGT or until the engines are about to quit.

2) Lean on descent. Keep engine temps up.

3) Do NOT lean on climb!

4) lean ROP or LOP to >60 ROP if necessary... depending on power.

5) Never start the engines unless you are going to fly.

6) never fly for less than 1 hr.

7) do NOT run at low power settings (<50%) for any length of time unless you lean to peak EGT! PEAK EGT!

8) Do not idle the engines for any length of time. I get my clearances and ATIS with a handheld.

9) Keep up your temps by keeping cowl flaps closed except on climb. Try and keep them up to 190 deg (oil temp).

10) Insulate rear oil tube to keep condensation down on rear engine.

If you adhere to the above rules you will NOT have any problems. I have followed these rules for many years flying Cessna products and it does make a difference..

Fresh oil is cheaper than new engines. Leaning saves fuel and eliminates carbon.

[JAG]

JMH,

question #1: I noticed that you may have two different temperature scales for your cylinder temps. 190 Celsius is 374 Fahrenheit - which is a perfect temp for your cylinder heads. Continental recommends an optimal temperature of 380 degrees F for your cylinder heads.

On your note about item 9 - yes, I think this should be cylinder head temp and not oil.

Question #2: I am not a "by the numbers guy" as that. Read John Deacon's information online (pelican's Perch on Avweb, #63 through #66) to understand more about the combustion process. This is essential reading for anyone with an injected NA engine, especially our Skymasters.

Here is a table (Attached) that I developed from researching the requirements from Cessna and Continental for my 1966 Cessna 337A.

Jeff

[mshac]

I've seen a thing or two on the internet, but I do believe this takes the cake for oldest thread ever brought back to life The OP likely had a dial-up modem connection through AOL...

[JAG]

JMH,

I just want to add a bit more of a response to your question #1.

I have my engine monitor set to give me a "yellow warning" at 400 degrees F on the cylinder head temps, and "red" at 420 degrees F. The reason I did this, is that for my aircraft (NA engine), those temperatures will ensure I have the correct mixture and that I am not doing damage to my cylinders. See also this article from John Deacon https://www.avweb.com/features_old/p...mixture-magic/ ).

Sometimes, in the heat of the summer here in Texas, I may hit 400 degrees CHT on a cylinder or two on the ground, after run-up. to get cool them off, (if this happens), I ensure I am into wind (if possible) and idle the rear engine and run the front engine up for a bit to get airflow to the rear - and this brings it down should this happen. As long as I do my run-up into wind and do the rear engine first, I have almost eliminated this event.

On Take-off, my cylinder head temps do not normally exceed 340 degrees F - I have spent a lot of time ensuring my fuel pumps are set up correctly, and I run at the top end of the fuel flow when I set them up. I rarely see cylinders going above 360 degrees in the climb for the warmest one, coolest one is around 330 degrees. In cruise, I am always closing the cowl flaps. Warmest cylinder I have experienced in cruise, leaned out, is 384 degrees.

I hope this helps give some perspective. There are a lot of opinions out there, different techniques to run your engines, and even engines having their own personality. Read the articles I indicate will really give you some understanding and help you determine how you want to run your engines.

Have fun with the new engine monitor!
Jeff