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Too-cool cylinders a concern?

prkaye

Well Known Member
I'm going to be doing more winter flying this year than i have in the past. Winters in Ottawa Canada get pretty cold. My IFR instructor has commented on how cool my Cylinders get on low-power approaches, even in relatively warm outside air surface temps of 0 degrees C (in Feb they'll be down to -20C or colder). The cylinders get down into the low-mid 200 degrees range. She has suggested i look into some kind of baffles or something to keep them warmer.
I've always been very concerned and careful about cylinder temps getting too high, but it never occurred to me that over-cool cylinders could be problematic.
Thoughts?
 
Too Cool

Indeed, there is a sweet spot for temperature in the mid to low mid 300s.

Overhaul guys speak to the problems of running too cool.
 
too cool

Pretty hard to do anything about it while doing low power approaches.

In normal cruise (8500', max MP, 2300 RPM) I would aim for 350 on cylinders.
 
Hi Stu, i just noticed your auto-sig, and checked-out some of your videos... very cool! I flew my RV-9A out to Moose Jaw (from Ottawa) years ago to visit my buddy Rhett Chambers who was the CFI at the Big 2. I went on to Calgary as well. It was an awesome trip.
Back in 2016 my daughter and I spent a day with the Snowbirds in Tillsonburg - they were there prepping/practicing for an airshow the next day and Rhett connected me with Morgan Strachan, who was one of the pilots at that time. My RV is painted in the colours of the Golden Centennaires, so I got some cool pictures of my plane parked with the Tutors :)
If you're ever in Ottawa, let me know. My RV is at CYSH.



 
Not talking shock cooling here. Too cool will more likely lead to wear related issues versus something catastrophic. The cylinder walls are only straight at one temperature; probably 350 degF-ish. Prolonged operation too far/cool side from the design point (very relative and non-precise, sorry) will slowly wear a step in the upper cylinder wall over time —> loss of compression, higher oil consumption. More extreme circumstances can flex-> fatigue -> crack rings.

The related power plants that many here rag on are quite robust. There’s not anything you can do about the ambient. There are complex ways to manage engine cooling flow. I believe managing your PP operation for the conditions, similar the consideration you do at startup, is your best defense. Being cognizant of the effects is the first step. You’ll hear various differing opinions. Listen to everyone and make the best choice for you/your equipment. I’m
 
FWIW, the Lycoming operator’s manual for the O-320 series engines states:
"At Bayonet Location - For maximum service life of the engine, maintain cylinder head temperatures between 150°F (66°C) and 435°F (223.86°C) during continuous operation."​
For the O-360 series engines, it states:

"At Bayonet Location - For maximum service life of the engine maintain cylinder head temperature between 150°F and 400°F during continuous operation."
 
FWIW, the Lycoming operator’s manual for the O-320 series engines states:
"At Bayonet Location - For maximum service life of the engine, maintain cylinder head temperatures between 150°F (66°C) and 435°F (223.86°C) during continuous operation."​
For the O-360 series engines, it states:

"At Bayonet Location - For maximum service life of the engine maintain cylinder head temperature between 150°F and 400°F during continuous operation."

Right. For continuous operation, maintain CHT’s in those ranges. We generally don’t have to worry too much about shock cooling on our Lycoming engines. We don’t continually operate or engines at the cooler temperatures we can see during an idle power landing. Cooling your engine from 350 to 250, or 200 during your approach and landing isn’t a problem. Shock cooling was a definite concern on the larger radials, especially the turbo-compound radials, but not on our 4 or 6 cylinder Lycomings. I’ve done many touch and goes where my idle power CHT’s are around 200* on colder days, and then added full power for my go. My CHT’s would increase to 300 - 320 on the go, but then pulling the power back to stay in the pattern, would level off, then decrease. This is not a problem. I don’t think shock cooling is a concern for most of us.
 
my CHT's run even cooler, especially in winter, so i investigated the issue. the bottom line i came to is... no problem.

the only problem could be the lead scavenging compound that is added to Avgas 100LL to mitigate the negative effects of the lead to the engine. these scavengers need some minimum temps in the cylinder to do a good job. i believe somewhere in the neighborhood of 350 F.

if you you use lead free gas that problem should be mute.
 
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