Shock cooling

[Tom-D]

Why? Stage cooling is unnecessary unless you're exceeding CHT limits and abusing your engine to begin with.

Ed Zakery.

 

[poadeleted20]

If you run your engine hot enough to harm the aluminum cylinder, you will certainly have valve guide, ring and piston problems too, so how can we blame shock cooling for the problems?

I didn't, and I don't.

One more time...

You can't cool your engine fast enough to cause cracking (the usual consequence blamed on "shock cooling"). You can cool your engine fast enough to cause accelerated piston righ/cylindar wall wear and reduce engine life. And Lycoming says the same. Fly accordingly if you want to maximize engine life and reliability.

 

[Tom-D]

"Properties" covers a lot of ground. As far as mechanical properties go, generally

yer splitting hairs, and going theory on me, trying to wake a dead boogy man.

shock cooling is a theory left over from the operators of the large radial engines that had a large amount of hidden cylinders in the rear rows that did not cool all that well. the closest you can come to that in a flat engine is when the baffling is bad and cowling is of a poor design.



I'm not saying shock cooling is a problem, just so we're clear.

When you can show the alloy of the aluminum cylinder heads, we can talk annealing temps. or changing the molecular structure of the alloy.

until then, I'll stand by with my statement

 

[Tom-D]

I didn't, and I don't.

One more time...

You can't cool your engine fast enough to cause cracking (the usual consequence blamed on "shock cooling"). You can cool your engine fast enough to cause accelerated piston ring/cylinder wall wear and reduce engine life. And Lycoming says the same. Fly accordingly if you want to maximize engine life and reliability.

I wasn't disagreeing with you, simply expounding on your comment.

OBTW, Lycoming has blamed a lot of things for their engine rapid piston pin wear. and cylinder failures in the past, why do you think they are doing any different now?

 

[skidoo]

Great points of view! So, if one doesn't get the CHT too hot, one should get good TBO life. Sounds like going from say 380F CHT to 280F CHT in a few minutes should be fine.

I am wondering what am I risking if I run cruise at low power and the CHT just stays from 280 to 310F? Can one run it too cold?

 

[Tom-D]

Great points of view! So, if one doesn't get the CHT too hot, one should get good TBO life. Sounds like going from say 380F CHT to 280F CHT in a few minutes should be fine.

that should be no problem.350-380 is great 280 is maybe too cool except maybe on approach.

I am wondering what am I risking if I run cruise at low power and the CHT just stays from 280 to 310F? Can one run it too cold?

Yes you can run too cool, but for a very different issue.

your oil temp should be hot enough to boil out the water that collects in your engine. 200F oil temp should be hot enough for that purpose, when you run long enough to get the job done.

 

[Inverted]

Why? Stage cooling is unnecessary unless you're exceeding CHT limits and abusing your engine to begin with.

Ummm no. I have seen cracked cylinders from shock cooling. Many conditions have to be met to cause damage to an engine but it is 100% possible. I will remember not to fly a turbo aircraft with you.

 

[Inverted]

Great points of view! So, if one doesn't get the CHT too hot, one should get good TBO life. Sounds like going from say 380F CHT to 280F CHT in a few minutes should be fine.

I am wondering what am I risking if I run cruise at low power and the CHT just stays from 280 to 310F? Can one run it too cold?

It is not about allowing the CHT's to get too hot. Shock cooling is the problem of CHT's getting too cool. Aircraft design, speed, cowling design and engine design all play into monitoring CHT's, and EGT's

People don't seem to realize that shock cooling can happen if you descend to rapidly, just as easily as not stage cooling the engine. If you descend at 500fpm without stage cooling you are more than likely to be 100% ok. If you create a situate where the engine is heat soaked with a steady state temp, CHT's warm and stabilized, then put the engine into a situation where it is allowed to cool too quickly, that is where the problems come from. It may not happen the first time you do it, it may never happen. But it common sense, if you allow different metals that cool and contract too rapidly, you will get abnormal, excessive wear.

 

[Trapper John]

When you can show the alloy of the aluminum cylinder heads, we can talk annealing temps. or changing the molecular structure of the alloy.

until then, I'll stand by with my statement

I'm not entirely sure what your statement is. If your statement is that an aluminum alloy casting can be heated to 830 F without changing its properties, that's not correct. No boogeyman, just basic materials science.

 

[Ted]

To answer the original question:

The best thing to do is to plan ahead as best you can. You'd also be surprised how well you can still keep roughly 1"/minute power reductions in effect and still do slam dunks. Your speed may get up high, but the nice thing about 172s and such is that they slow down pretty well, too. As you get up to Mooneys and other slippery aircraft, it simply requires more planning.

As to the shock cooling fairy: I don't care if it exists or not. It's unprofessional to do rapid power changes with high rates of descent in an unpressurized piston twin. Sure, there are times when it has to be done. However, those times are exceedingly rare if you plan properly and fly with this in mind. If you fly with the intent of doing your 1"/minute power reductions as you come in, it will help make you a better, smoother pilot. Then that extra workload capacity you have will help you when you get into a tight situation.

 

[Tom-D]

I'm not entirely sure what your statement is. If your statement is that an aluminum alloy casting can be heated to 830 F without changing its properties, that's not correct. No boogeyman, just basic materials science.

I'm saying that the temps required to alter the alloy is way higher than any engine will see in normal usage. If it were not we would see a lot more failures in low time cylinders.

 

[Tom-D]

It is not about allowing the CHT's to get too hot. Shock cooling is the problem of CHT's getting too cool..

If that were true, Why didn't Bob Hover and other acro pilots have more engine failures?

 

[Tom-D]

Ummm no. I have seen cracked cylinders from shock cooling. Many conditions have to be met to cause damage to an engine but it is 100% possible. I will remember not to fly a turbo aircraft with you.

I do not believe the cylinders you saw were cracked by shock cooling, Glider tow pilots and jump aircraft, slam dunk there engines time after time and they do not suffer cracking, they do see piston scuffing more than other operators but no more cracking than normal operators.

 

[Ted]

If that were true, Why didn't Bob Hover and other acro pilots have more engine failures?

Because there's a big difference between something that causes accelerated wear and something that causes immediate failure. You even admit this by increased piston scuffing that glider pilots show.

Take the example of letting geared engines windmill, which ends up causing the gears to slap back and forth, vs. having a load on them applied in one direction. You do it once, it should still make TBO. You keep on doing it, well...

 

[Tom-D]

Because there's a big difference between something that causes accelerated wear and something that causes immediate failure. You even admit this by increased piston scuffing that glider pilots show.

Take the example of letting geared engines windmill, which ends up causing the gears to slap back and forth, vs. having a load on them applied in one direction. You do it once, it should still make TBO. You keep on doing it, well...

gears resonance, and thermal stresses are two way different issues.

Piston/to cylinder scuffing occurs when the cylinder becomes smaller than the ring end gap can close, and compensate for the reduced size of the cylinder. The Lycoming 180 horse ring end gap given in the table of limits is item 607, and notes that the ring end gap must not be below .075 inches, do the math, see how much the barrel must contract, to close that gap. You'll see it is nearly impossible to have that occur.
banner towers and jump aircraft have other contributing factors that cause piston failures. shock cooling isn't the major one.

 

[Ted]

gears resonance, and thermal stresses are two way different issues.

They are, but the principle still applies. You can do things that won't cause an immediate failure, but will contribute to a failure later.

Piston/to cylinder scuffing occurs when the cylinder becomes smaller than the ring end gap can close, and compensate for the reduced size of the cylinder. The Lycoming 180 horse ring end gap given in the table of limits is item 607, and notes that the ring end gap must not be below .075 inches, do the math, see how much the barrel must contract, to close that gap. You'll see it is nearly impossible to have that occur.

No, piston to cylinder scuffing occurs when the barrel shrinks smaller than the cylinder. If the whole assembling shrinks to the point where the ring is interfering with itself, then something will give, and it won't be pretty.

banner towers and jump aircraft have other contributing factors that cause piston failures. shock cooling isn't the major one.

And who says that the failure mode is necessarily cylinder cracking? You come back to that frequently as proof that shock cooling definitively does not exist. While that is one failure more that can exist, there are lots of other things that can cause your wallet to regret your actions.

 

[SCCutler]

I knew a guy, had heartworms in an O-320.

 

[Tom-D]

No, piston to cylinder scuffing occurs when the barrel shrinks smaller than the cylinder.

No,,,,,, the barrel is the steel cylinder that the piston/ring assembly rides in.

And who says that the failure mode is necessarily cylinder cracking? You come back to that frequently as proof that shock cooling definitively does not exist. While that is one failure more that can exist, there are lots of other things that can cause your wallet to regret your actions.

shock cooling in every discussion (except maybe this one) is about thermal expansion and contraction causing cracking.

If thermal expansion could cause piston scuffing why wouldn't they scuff on start up? the piston is aluminum and is closer to the fire than any other part of the engine, and is only cooled by oil wash. when the cylinder barrel is steel, expands less and is being cooled by air flow?

simply doesn't make sense

 

[Tom-D]

I knew a guy, had heartworms in an O-320.

I knew a guy who had a headache every time he thought, so he was advised to stop thinking.

 

[steingar]

I'm with Tom on this one. You want to see shock cooling? Fly in cold rain. Water has a much higher specific heat than air. Add to that the fact that a fair amount of that water is carrying away even larger amounts of energy by evaporating into steam.

I'm also with Ted though. Part of being a good pilot (in my own humble highly uninformed opinion) is to stay ahead of the aircraft. You should have a pretty good idea of when you are going to have to descend, and should be able to plan accordingly. I imagine that it gets more difficult with slicker aircraft, but that's why one shouldn't fly such if one isn't a very good pilot.

 

[poadeleted20]

Yes you can run too cool, but for a very different issue.

your oil temp should be hot enough to boil out the water that collects in your engine. 200F oil temp should be hot enough for that purpose, when you run long enough to get the job done.

Agreed in general, but Lycoming says that you only need 160-170F for 30 minutes "to get the job done." If I needed to get to 200F, I'd be in trouble, because the only time my oil gets that hot is climbing in the summer.

 

[poadeleted20]

I'm with Tom on this one. You want to see shock cooling? Fly in cold rain. Water has a much higher specific heat than air. Add to that the fact that a fair amount of that water is carrying away even larger amounts of energy by evaporating into steam.

Even flying into an area of cold rain isn't enough to get the 1000's of degrees per second necessary for quench cracking. It may lower your CHT's some, but unless you also chop the throttle as you enter the rain, not at an "alarming" rate.

 

[Ted]

No,,,,,, the barrel is the steel cylinder that the piston/ring assembly rides in.

Sorry, my wording wording was incorrect. It happens when the cylinder barrel shrinks smaller than the piston inside it. Still, that's different than what you said. It doesn't have to do with the rings. If the rings are interfering, then you're in a world of hurt.

shock cooling in every discussion (except maybe this one) is about thermal expansion and contraction causing cracking.

You're the primary person who I ever see reference that, you cite that shock cooling doesn't have any effect on the engine because cylinders don't crack immediately when people operate their engines in a manner conducive to shock cooling. I'm saying that is nowhere near sufficient evidence to prove or disprove the theory.

If thermal expansion could cause piston scuffing why wouldn't they scuff on start up? the piston is aluminum and is closer to the fire than any other part of the engine, and is only cooled by oil wash. when the cylinder barrel is steel, expands less and is being cooled by air flow?

simply doesn't make sense

They do scuff on startup if your temperatures are too cold. That's one of the reasons why you're supposed to preheat. Don't believe me? Build an engine and give it a proper break-in. Then start it at 0F with no pre-heat 20 times in a row. After that, tear it down. Make sure to let it sit overnight each time so everything is cold. Tell me what you find.

 

[Tom-D]

T You can do things that won't cause an immediate failure, but will contribute to a failure later..

That is certainly true, but shock cooling isn't one of them. Shock cooling is good in theory, but the engines we fly have compensated for it in their design, and it simply can't happen. the clearances between the piston to cylinder wall and the ring end gaps are way to big to allow it.

 

[Tom-D]

Even flying into an area of cold rain isn't enough to get the 1000's of degrees per second necessary for quench cracking. It may lower your CHT's some, but unless you also chop the throttle as you enter the rain, not at an "alarming" rate.

very very true, shock cooling simply does not happen in our engines no matter how badly we treat them.

piston scuffing and cylinder cracking are nearly 100% caused by other reasons

 

[Ted]

I'm with Tom on this one. You want to see shock cooling? Fly in cold rain. Water has a much higher specific heat than air. Add to that the fact that a fair amount of that water is carrying away even larger amounts of energy by evaporating into steam.

That doesn't cause it, though. Watch your CHTs when that happens, and you'll note that they'll go down a pretty insignificant amount. The rain you fly through is not a garden hose typically. And even when I've flown through garden hose-type rain (more than once...), I've only seen about a 10-15F drop in CHTs. I also note that my OAT drops when I'm in that rain typically, and so it's hard to say how much is the water vs. the OAT. You'll see a much more rapid rate of decrease in CHT if you chop the power and point the nose at the ground than if you fly through rain.

Where the water hits isn't the hottest part of the cylinder, either. So your delta T is lower, meaning slower heat transfer. Then the water heats up, and your heat transfer goes down further.

I'm also with Ted though. Part of being a good pilot (in my own humble highly uninformed opinion) is to stay ahead of the aircraft. You should have a pretty good idea of when you are going to have to descend, and should be able to plan accordingly. I imagine that it gets more difficult with slicker aircraft, but that's why one shouldn't fly such if one isn't a very good pilot.

Which is why I don't care if the shock cooling fairy exists or not.

 

[Ted]

That is certainly true, but shock cooling isn't one of them. Shock cooling is good in theory, but the engines we fly have compensated for it in their design, and it simply can't happen. the clearances between the piston to cylinder wall and the ring end gaps are way to big to allow it.

Tom, you simply do not have the evidence to prove or disprove that.

 

[Tom-D]

S
They do scuff on startup if your temperatures are too cold. That's one of the reasons why you're supposed to preheat. Don't believe me? Build an engine and give it a proper break-in. Then start it at 0F with no pre-heat 20 times in a row. After that, tear it down. Make sure to let it sit overnight each time so everything is cold. Tell me what you find.

no flat engine will cool as well as a radial where all cylinders are in the prop blast, I have operated the 1340 and the 975 in temps as cold as -40, and you heat the oil tank, oil pump and carb, start them and go.

they don't scuff the pistons.

 

[Tom-D]

Tom, you simply do not have the evidence to prove or disprove that.

The dificult part of the discussion is no one has proof of their belief on either side.

but I do have nearly 50 years of engine overhaul experience that has shown me shock cooling does not exist. in the engines we fly.

there are way to many operators abusing their engines with out major failures to say it is the big bad boogy man that the industry thinks it is.

 

[poadeleted20]

Unfortunately, Ted's employer does not permit him to say what he does or where he works, but I do know, and on this issue, no one could be more qualified to give reliable information -- not even someone who's been a mechanic for 50 years. On this issue, you can take what Ted says to the bank.

 

[Ted]

no flat engine will cool as well as a radial where all cylinders are in the prop blast, I have operated the 1340 and the 975 in temps as cold as -40, and you heat the oil tank, oil pump and carb, start them and go.

they don't scuff the pistons.

And your experience with radials has only anecdoatal relevance to what everyone else on this forum flies, as the engines are significantly larger with different clearances. I have no idea what will happen with a 1340 or a 975 - I've never operated them. So to that, I don't know. I do know what happens on our horizontally opposed 4 and 6-cylinder engines.

And you also cheated. I said no preheat. That includes the oil, oil pump, and carb. You also say you've operated them as low as -40F, but how many cold starts in a row?

The dificult part of the discussion is no one has proof of their belief on either side.

Then why are you proporting to have knowledge that you don't? Note, I haven't once said that shock cooling does or does not exist. I maintain my position that I don't care if it exists or not, and I maintain that you don't have any data to prove that it doesn't exist. The advice you are giving people is at best with insufficient backing.

but I do have nearly 50 years of engine overhaul experience that has shown me shock cooling does not exist. in the engines we fly.

there are way to many operators abusing their engines with out major failures to say it is the big bad boogy man that the industry thinks it is.

And you are also implying the only possible consequence is a catastrohpic failure, which is also not true, nor is it what I've seen the industry claim in its publications.

When you can show data that comprehensively supports your theory, get back to us. In the mean time, please quantify your statements accordingly.

 

[Jaybird180]

Unfortunately, Ted's employer does not permit him to say what he does or where he works, but I do know, and on this issue, no one could be more qualified to give reliable information -- not even someone who's been a mechanic for 50 years. On this issue, you can take what Ted says to the bank.

Honestly, I've lost track of what his point is...

Then why are you proporting to have knowledge that you don't? Note, I haven't once said that shock cooling does or does not exist. I maintain my position that I don't care if it exists or not, and I maintain that you don't have any data to prove that it doesn't exist. The advice you are giving people is at best with insufficient backing.

Ah, Glad he answered my question.

I recall in reading the Lycoming 'care and feeding' document that they think it exists. Seems to me to make sense, but I guess the question is how do you reproduce their results?

In my mind, as I've understood the term, a shock cooled engine will fail immediately. If it doesn't crack and fail prior to touchdown, then something else is occurring. Uneven cooling I think can cause premature wear and cylinder warping. But then again, the oil capacity (a fluid separating the piston from cylinder walls) is heated and incompressible.

Am I kunfuzed yet?

 

[poadeleted20]

I recall in reading the Lycoming 'care and feeding' document that they think it exists.

I don't think they use the term "shock cooling." They refer to accelerated/abnormal wear, and their concerns are long-term, not immediate.

In my mind, as I've understood the term, a shock cooled engine will fail immediately. If it doesn't crack and fail prior to touchdown, then something else is occurring.

If you could cool the engine that fast (1000's of degrees per second), yes, that's what would happen. But you can't, so it's not an issue.

Uneven cooling I think can cause premature wear and cylinder warping.

I suppose it could, but what Ted and I talking about is the head cooling faster than the piston, not uneven cooling of the head itself. But yes, that difference in cooling rate can cause "premature wear."

But then again, the oil capacity (a fluid separating the piston from cylinder walls) is heated and incompressible.

Oil may be incompressible, but unless it's contained, it will escape from the gap between the ring and wall, and since it's contained on only two sides (the ring side and the wall side), it can be forced out of that gap if that already miniscule gap closes.

 

[Ted]

Ah, Glad he answered my question.

The point is that if you fly like you ought to, then it's irrelevant. When I instruct pilots, I teach them gradual power changes, because it's how I think people ought to fly.

We're also ignoring the fact that dynamic counterweights also don't appreciate rapid power changes

I recall in reading the Lycoming 'care and feeding' document that they think it exists. Seems to me to make sense, but I guess the question is how do you reproduce their results?

Well, you're the person with the engine controls, so you ultimately have to decide how to operate your airplane. A lot of people choose not to follow the manufacturer's recommendations, and that's their choice as much as it is to follow. Either way, you're the one paying the bills. The reality is that you as an individual can't reproduce the service history and experimental testing that manufacturers or large overhaul shops do. That's part of why it's interesting to talk to these people. Everyone has their own opinion, but few have enough data to back it up. It's hard to argue with the fact that a smooth pilot is typically better appreciated by his or her passengers, and reduces propensity to having the previous meal regurgitated all over the plane.

In my mind, as I've understood the term, a shock cooled engine will fail immediately. If it doesn't crack and fail prior to touchdown, then something else is occurring. Uneven cooling I think can cause premature wear and cylinder warping. But then again, the oil capacity (a fluid separating the piston from cylinder walls) is heated and incompressible.

Am I kunfuzed yet?

Immediate failure is not a requirement. Tom perpetuates that's what the term means, but I haven't seen any publication that agrees with him. I'm not sure what your point was with the oil.

 

[Jaybird180]

Re: the Oil

I forgot about the ring gap, which Ron reminded me of. My point at the time is that the piston and cylider walls don't touch and the oil flowing between helps to reach temperature equilibrium. But Ron has shown that's a bum idea.

 

[Tom-D]

I don't think they use the term "shock cooling." They refer to accelerated/abnormal wear, and their concerns are long-term, not immediate.

That is exactly why you install new cylinders at overhaul, and not suffer the failures of old high time cylinders.

If you could cool the engine that fast (1000's of degrees per second), yes, that's what would happen. But you can't, so it's not an issue.

I suppose it could, but what Ted and I talking about is the head cooling faster than the piston, not uneven cooling of the head itself. But yes, that difference in cooling rate can cause "premature wear."

Let's be clear, the piston never touches the cylinder head, the cylinder head is the aluminum casting that attaches to the top of the steel cylinder barrel. it contains the valve assemblies, and forms the combustion chamber. It does not matter how fast it cools or heats as far as the piston is concerned.


Oil may be incompressible, but unless it's contained, it will escape from the gap between the ring and wall, and since it's contained on only two sides (the ring side and the wall side), it can be forced out of that gap if that already miniscule gap closes.

Have you ever held a piston in your hand and looked at it? there are holes behind the oil control ring which allow oil to pass out of the ring grove into the interior of the piston.

The top compression rings do not always have these holes, because only a limited oil supply is allowed to pass the oil control ring, that oil which does pass gets behind the compression ring and the heat of the piston causes it to become hard carbon limiting the movement of the ring, this causes wear on the cylinder walls, this is why you try your best to not run high cylinder temps

Lycoming has done nothing in the past 50 years to eliminate the problem except to issue a CYA statement to limit the CHTs in their engines.

 

[Ted]

That is exactly why you install new cylinders at overhaul, and not suffer the failures of old high time cylinders.

Wait a second, it was only a few threads ago you were advocating sending old cylinders out for overhaul and using those.

I know the answer is "it depends", but your statements don't make that clear at all.

Let's be clear, the piston never touches the cylinder head, the cylinder head is the aluminum casting that attaches to the top of the steel cylinder barrel. it contains the valve assemblies, and forms the combustion chamber. It does not matter how fast it cools or heats as far as the piston is concerned.

That depends - after all, the head screws onto the barrel. Remember that cylinder barrel temperatures have a definite correlation with head temperatures that has been tested. That is true, though, that the piston technically goes in the cylinder barrel, not the head.

Have you ever held a piston in your hand and looked at it? there are holes behind the oil control ring which allow oil to pass out of the ring grove into the interior of the piston.

The top compression rings do not always have these holes, because only a limited oil supply is allowed to pass the oil control ring, that oil which does pass gets behind the compression ring and the heat of the piston causes it to become hard carbon limiting the movement of the ring, this causes wear on the cylinder walls, this is why you try your best to not run high cylinder temps

Lycoming has done nothing in the past 50 years to eliminate the problem except to issue a CYA statement to limit the CHTs in their engines.

All engines have CHT limits, even Continentals (which are lower than Lycomings for all the ones I've seen). It's been well established by all manufacturers that limits are not goals in most cases, and as such there are recommended operating temperatures that are lower than the limits. How exactly is establishing of a limit, supplemented with recommended operational procedures for maximum service life, an indication of a problem?

Furthermore, go run a Continental with the CHTs at the limit as a matter of procedure and tell me how long the heads last. I don't think you'll be happy with the result. The local Malibu here with a TSIO-520 is lucky to get 600 hours out of his heads before they need an overhaul.

FWIW, I run my Lycomings and Continentals the same way when it comes to CHTs.

 

[Tom-D]

Wait a second, it was only a few threads ago you were advocating sending old cylinders out for overhaul and using those.

we knew those cylinders were 900 TT the engine was overhauled, so it could be placed in a NEW cub that was going to be sold.

I have never advocated using high time cylinders, in fact you can refer to any of my posts and see I preach If you don't know cylinder time don't reuse them.

I know the answer is "it depends", but your statements don't make that clear at all.

That depends - after all, the head screws onto the barrel. Remember that cylinder barrel temperatures have a definite correlation with head temperatures that has been tested. That is true, though, that the piston technically goes in the cylinder barrel, not the head.

There may be a correlation between the two, that does not mean the cylinder assembly be effected by shock cooling.



All engines have CHT limits, even Continentals (which are lower than Lycomings for all the ones I've seen). It's been well established by all manufacturers that limits are not goals in most cases, and as such there are recommended operating temperatures that are lower than the limits. How exactly is establishing of a limit, supplemented with recommended operational procedures for maximum service life, an indication of a problem?

Furthermore, go run a Continental with the CHTs at the limit as a matter of procedure and tell me how long the heads last. I don't think you'll be happy with the result. The local Malibu here with a TSIO-520 is lucky to get 600 hours out of his heads before they need an overhaul.

FWIW, I run my Lycomings and Continentals the same way when it comes to CHTs.

Ron and I both agree these engines will never see operating temps that will harm the cylinders at any rate you can cool them, thus shock cooling is a myth.

AS far as one manufacturer being better than the other, wear and heat doesn't care what the data tag says. any manufactured machine item has their limits. These little flat engine are no different than any engine, you turn the heat up, you can turn the time down. the rate of cooling has nothing to do with it.

 

[PittsDriver]

Ron and I both agree these engines will never see operating temps that will harm the cylinders at any rate you can cool them, thus shock cooling is a myth.

AS far as one manufacturer being better than the other, wear and heat doesn't care what the data tag says. any manufactured machine item has their limits. These little flat engine are no different than any engine, you turn the heat up, you can turn the time down. the rate of cooling has nothing to do with it.

I may not be remembering correctly but didn't the APS folks prove that heat wasn't as big a factor in engine wear and reliability as head pressures? IOW, peak head pressures were found at 50 - 80 ROP and this was worse than operating at the same temp LOP. I don't have the reference handy and will try to find it.

 

[Ted]

Ron and I both agree these engines will never see operating temps that will harm the cylinders at any rate you can cool them, thus shock cooling is a myth.

You are referring to catastrophic failure, which is not the only failure mode that exists.

AS far as one manufacturer being better than the other, wear and heat doesn't care what the data tag says. any manufactured machine item has their limits. These little flat engine are no different than any engine, you turn the heat up, you can turn the time down. the rate of cooling has nothing to do with it.

So why are you stating that Lycomings have a problem because there's a statement you shouldn't run your CHTs near the limit? That's true for any engine.

Your statements are nowhere near clear nor in agreement with eachother...