The International Cessna 170 Association

Wondering if my temps are "average". OAT 68-70 @ 2500 msl; 2500-2550 rpm; level flt; leaned mixture. Exhaust temp - 1300. Cyl temp - 290-300. Cyl temp on # 2 cyl and on top plug.
Prior to, hopefully, fixing an exhaust leak on # 2, I was getting exhaust grey stuff on the sparkplug and some damage to exterior of the plug. Cyl temp was on the bottom plug in # 2. I suspect the exhaust leak was contributing to a climb cyl temp of 400 & a cruise temp of 375. Not sure what the recommended location (top or bottom) plug for the cyl temp.
Frank

This is something that I have never really thought about on the location of the cylinder temp prob. I have always fitted to the bottom plug and on the hottest cylinder regardless if it was a 4 or 6 cylinder engine . The first figures given sound a little cool for cylinder temps but any thing under 400 degs is ok. I aim for max 350deg for CHT . If you can talk to Frank Mc Bride from Lycoming [he is retired] but has a blogg on a avaition mag web site . People say that 500degs is the max for CHT. I wouldn’t go there due to advice from a couple of engine manufacturers.

For CHTs I see 350 or so on cyls 1-4 and about 100 cooler on 5 and 6. EGTs are all over the place, hottest usually #2, sometimes #3 at 1450-1475, with the others ranging down to nearly 1300. I usually cruise 2600 rpm, lean by the book (lean slowly till rough, then richen slightly). My cylinders are ECI with the bayonet fittings for the CHT probes. All EGT probes are 2 inches below the exhaust flange.

I used to get all bent and twisted over my EGT,s But was advised that EGT,s are not all that critical. The early EGT gauges didn’t have calibration marks on them only lines in 25 deg spacing. The main concern is the CHT temperatures and where on the cylinder head is the temperature is measured. The temp probe that part of the spark plug gasket has a different temperature than the probe that is part of a insert into the cylinder head . So when 500 deg is mentioned as the highest temperature one has to ask where is this temperature measured. Cylinder heads have all uneven temperatures all over casting . Some areas can be over 650 degs when the probe is saying 500degs . These hot spots have a tendency to crack as often as the area near this hot spot is often a very cool area [fins] . My aim is to have a cylinder head heat soaked totally around 350 deg . Aim , I said. Originally [many years ago ]when I was flying and having my cylinder heads at 400 degs plus , I would drop the nose and richen up quickly to drop the CHT,s . I was flying with a tech rep from Lycoming when I did this and he advised me strongly do not do this but do changes s l o w l y. He explained what I was doing was shock cooling and sets up big stresses between the head and cylinder barrel and often cracks will appear or cylinder separation .

This information was for entertainment reasons only and one should consult your flight /maintenance manual and all relevant FAA documents .

I found using a laser temp tool and the engine under full power with out cowls was very informative on different temperatures around the engine . I,was checking my CHT probes on each cylinder for accuracy and found a world of discovery .

I have a 60 hr. SMOH 0-300, cruising at 3000, OAT +20 with lean condition at 2500 RPM, I always have solid 300 CHT.
I have never had Oil under 200 degrees running Aeroshell 80W, no extra additives. Told buyold timer he uses AvLube Product and says lowers temp and give trouble free operation. Who knows? Regards, JD Smith

Checked on my exhaust leak repair and moved the cyl head temp ring to the lower plug (#2 cyl). Climb temp returned to between 375 & 390. Cruise dropped back to 375. Exhaust temp at 1300. Guess that is where its going to be on my engine.

I have read articles and told by AP/IA's on updraft engines the CHT Probe should be on a top spark plug, mine is on No #6 Top. Appreciate any tips on Oil Additive, Cam Lube for LYC, how about AV Lube for Cont? Marvel Mystery in Fuel? Thanks JD Smith

The only oil additive that I would use is already premixed into Phillips oil. That Marvel mystery oil is one big con.
A friend of mine who was chemist for Mobil oil for many years analyzed it and came to the conclusion it was kerosene,coloring , and some auto transmission oil . There was a number of batches analyzed and they found it wasnt consistent with each batch . He strongly advised me that he wouldn’t put it in his worn out lawn mower let alone a aircraft.
As I have writing this a colleague informed me there have been other people [professional chemists] have analyzed this product and came to the same conclusion .

ghostflyer wrote:.....
A friend of mine who was chemist for Mobil oil ...... strongly advised me that he wouldn’t put it in his worn out lawn mower let alone a aircraft.

And yet millions and millions of gallons of the stuff have past through engines of all sort since 1923 including at least one or two aircraft engines.

And there is no secret what it is today. I carry this in a note on my phone for just this occasion. The chemical break down is from the MSDS sheet. I don not remember who the author of the comments about each ingredient.

MMO

70% Light Aromatic Oil (Pale Oil)
- It is a Naphthenic Oil, so while it oxidizes faster than a Paraffinic oil, it does clean and dissolve sludge and carbon well and cleans up after itself from any oxidation. serves as base oil as well. [Naphthenic oils have more solvency and are more polar (they are attracted to metal more), but oxidize faster.

29% Mineral Spirits
- Cleans Varnish very well. General cleaner. Also acts as an antioxidant.

38 parts per million (ppm) Boron
- AW/EP agent, friction reducer, antioxidant

900 ppm Phosporous
- AW/EP agent

1/2% 1, 2 ortho-Dichlorobenzene
- EP agent as it interacts with Iron to form an Iron chloride barrier under any ZDDP or other AW additives. Also very good cleaner/solvent, and friction reducer

1/4% 1, 4 para-Dichlorobenzene
- EP agent as it interacts with Iron to form an Iron chloride barrier under any ZDDP or other AW additives. Also very good cleaner/solvent, and friction reducer

Oil of wintergreen - for the scent
- Not just for the cent, is also a cleaner. may aid lubricity.

Red Dye - for the color
- well this one just colors the stuff

I will pass this info on the Tim Slater who is now at BP and see what his comments are . I am also interested what effect it has on your seals ? On another note if it was the holy Gail why doesn’t oil companies recommend it or the aircraft /engine manufacturers recommend it . Unfortunately there are a number of urban myths around and due to the human psych we are looking for something that gives us a edge . Many of the big brand manufactures do this also so one has to be wary.

Do they have a green formulation?

ghostflyer wrote:I will pass this info on the Tim Slater who is now at BP and see what his comments are . I am also interested what effect it has on your seals ? On another note if it was the holy Gail why doesn’t oil companies recommend it or the aircraft /engine manufacturers recommend it . Unfortunately there are a number of urban myths around and due to the human psych we are looking for something that gives us a edge . Many of the big brand manufactures do this also so one has to be wary.

MMO has been used in thousands of engine and millions of hours. I personally never had one issue using it.

Is it the Holy Grail? No cause it's not approved which explains why aircraft manufacturers won't recommend it.

Why doesn't MMO get approval. I guess since they've been making and selling the stuff since 1923 and don't seem to have any trouble selling it, they don't care to go through the trouble.

I used it for a period in my Cub and 170 to eliminate stuck valves. Never had a stuck valve using it.

I'm back from the 3-month vacation and ..what do I first see..?? MMO ..AGAIN!!! LOL!

White labs (Dallas) decoded MMO and said the same things others have reported.... It's a light kerosene/oil with dye, perfume, and trace additives of phosphorus. They also said the formula was inconsistently mixed from batch to batch. I've always thought that the phosphate was the magic ingredient as it's similar to TCP and EP/Extreme-Pressure additives in lube-oils. (EGTs of 1100 or more is necessary to gain any benefit from phosphate anti-fouling.)

I've not used it in my airplane but I've never detected any problem OR benefit in my ag engines. Of course, I'm also not consistent with application either and I believe it's most beneficial effects are psychological.... sorta like dark chocolate.

Frank, the Continental manuals all recommend the spark-plug-gasket type CHT probe be mounted on the Bottom plug, No. 2 Cylinder. It is (according to TCM) the hottest cylinder in this installation. (I'm guessing they know what they're saying and that they realize several different cooling baffle arrangements are possible in these airplanes.)

My own O-300 is so equipped and my (never calibrated/presumed accurate) CHT hovers at 180-220 degrees Centigrade (Texas) depending on flight conditions. That is equivalent to 350-425 approx in Fahrenheit. Continental states the CHT limit for this engine is 275C/525F. (They also recommend a cooling-off 300F prior to shut down, and is why I also recommend a few minutes below 1,000 RPM before shut down in order to avoid stuck valves. That is without regard to use of MMO or other snake oils.)

9976AJds wrote:I have read articles and told by AP/IA's on updraft engines the CHT Probe should be on a top spark plug, mine is on No #6 Top. Appreciate any tips on Oil Additive, Cam Lube for LYC, how about AV Lube for Cont? Marvel Mystery in Fuel? Thanks JD Smith

I realize this is an old thread, but found in a search as I'm exploring putting in an engine monitor. At any rate, our birds (170) are downdraft cooling. The Globe Swifts - another bird commonly found with the O-300 - uses updraft cooling and there your approach would be correct. For the 170, it should be the lower plug, #2 cylinder.

Also, the spark plug gasket CHT probes can read 25-50 degrees hotter due to their location next to the plug than if you had a "normal" CHT probe in the cylinder. Therefore, if you see a reading of 375 degrees, it is likely the "actual" CHT is closer to 325-350 (that is, the temp you'd see if you had a normal CHT probe).

bgiesbrecht wrote:

9976AJds wrote:I have read articles and told by AP/IA's on updraft engines the CHT Probe should be on a top spark plug, mine is on No #6 Top. Appreciate any tips on Oil Additive, Cam Lube for LYC, how about AV Lube for Cont? Marvel Mystery in Fuel? Thanks JD Smith

I realize this is an old thread, but found in a search as I'm exploring putting in an engine monitor. At any rate, our birds (170) are downdraft cooling. The Globe Swifts - another bird commonly found with the O-300 - uses updraft cooling and there your approach would be correct. For the 170, it should be the lower plug, #2 cylinder.

Also, the spark plug gasket CHT probes can read 25-50 degrees hotter due to their location next to the plug than if you had a "normal" CHT probe in the cylinder. Therefore, if you see a reading of 375 degrees, it is likely the "actual" CHT is closer to 325-350 (that is, the temp you'd see if you had a normal CHT probe).

We are discussing Cylinder HEAD Temperatures.
Continental specifies the use of a spark plug gasket type CHT probe. (the only other cylinder temp specified is a cyl base temp…not ordinarily instrumented except in test-cells.) From the X30013 Overhaul Manual: