Shock Cooling - Myth Busted!!
 

Here is a little story I thought I would share with you.


One of the great Old Wives Tales, Shock Cooling!

Well I am not sure how easy it would be to do this, apart from spear into a lake, that would do it for sure, but even in an extreme descent with 2000FPM plus ROD I can't seem to do it.

So here is the story, last Saturday returning from St George Qld to Caboolture (Brisbane) I climbed to FL130 and was enjoying 45 knots on the tail, so a GS of 210 knots. As I was about 20 minutes out, I advised BNE CEN that my TOD point was 46 miles from YCAB and that was 13 minutes, to allow for a 12000' descent to circuit area altitude. I do this so it helps them with all the crossing traffic I have going against the flow. My tracks are often a pain I am sure.

Anyway 13 minutes comes and goes, and I think any second now........10 minutes, hmmm I wonder if my mate is on BNE APP this afternoon. Anyway they are busy with jet traffic and RFDS etc into YBBN, so I figure I can fit in with whatever keeps everyone happy. At 6.5 minutes to run, 22NM to destination.....the following occurs;
BNE CEN: Lima November Lima, Descend 6000 and contact BNE APP on 124.7 , I do the read back and over I go to 124.7,
LNL: Brisbane Approach, Lima November Lima FL130 cleared 6000 and Visual.
BNE APP: Lima November Lima, cleared to leave on descent, Brisbane QNH 1014, good afternoon Brownie!
LNL: Cleared to leave on descent, 1014 LNL....and gooday to you NP and did you have something to do with the late descent?
BNE APP: I have NO Idea what you are talking about <laughing>
LNL: WATHCH THIS <laughing>

Now 6 minutes and 20 miles

Now not exceeding VNE (by TAS), and then as the bumpy bits over the mountains (ok hills) staying out of the yellow arc and not wanting to lose the game, I had a job to do. At times the ROD was around and over 2000 FPM, and I watched happily the CHT's very slowly decline. The Throttle was pulled right back and the RPM about half way down was increased to 2550 to help the cause. Pitch went from +1 in cruise to -8.5 at times and mostly -5 to -7 and this was a very different view of the Brisbane region.

So I have downloaded the data, and done a Delta T on CHT and the graph shows a flat line. The cumulative Delta T shows a greater ramp for the taxi and take off than at any point in the descent. Unfortunately the Delta T will not upload to the SAVVY site, however you can see the slope on the curves.

I have uploaded the file to the Savvy site, you can click on the extra displayed data to show Vert Speed or other things.

https://my.savvyanalysis.com/public/...1-b50788c2095a

No doubt some flat earthers will tell me that the cylinders will fall apart due cracks in a few hundred hours.

It is pretty hard to shock cool and engine that is already cool!

Shock Cooling - BUSTED! :}

Oh goodness what have you done?

Awesome graph..

If you zoom in on the descent you can see the CHT is steadily dropping at 10*/min
If only the data continued after shut down.. How long does it take the remaining 270* to dissipate??

I've got another one - is it the rate of cooling/heating, or the actual temp.

My understanding is that hotter temps, above 190-200degC result in significant cylinder wear.

But if you slowly cool the engine to 100-110 deg and then glide descend at high rates of descent, and the CHT remains stable, does the fact that the engine is turning over cooler (and tighter seals I guess?) result in significantly more wear, even at minimal power & RPM?

[I realise a go-around at low CHT will be where a lot of wear occurs, but like the op, I'm more interested in if running at low CHT in a glide actually does any damage]

Would like to see the same level of analysis on a parachuting aircraft Jabba.

Oh goodness what have you done?

Haha should be good.

Hope you have not jinxed yourself Jaba;)

I would have to agree, after probably 12000+ descents from 12000ft to SL in the Cessna 180/185, I have never experienced a cracked cylinder. I would always leave RPM at 2200 or 2300 and pin the MP at that as well when it caught up. Descent rate would be around 3000fpm and airspeed quite high in smooth air. In later years I had an engine monitor etc.
http://i303.photobucket.com/albums/n...s/DSC01500.jpg

http://i303.photobucket.com/albums/n...s/IMG_6836.jpg

What happened at 14:10 Jabba? (you didn't fart did you?)

Doggies \\ //

hehehhehehe :}

yeah I deliberately did all the bad things, throttle closed, increased RPM to increase ROD, left the mixture alone from what was 37-38 LPH in the cruise.

Ohh yes the graph after shut down!

Taxi in the temps went from 256 to 276 and then after shut down they went up! Then they went down at 1Deg F every 6 seconds, then the monitor was shut down.

So shut down is just as nasty! :} And maybe worse! No oils moving around :}:eek::} :E

Ohhh dear me...... seems those rednecks Braly Deakin and Atkinson were not talking out their data ports after all! :D

Jack you trouble maker!! Doggies!! \\ // from Jnr Jaba to ya!:ok: And happy fathers day for next Sunday!:ok:

I was just doing some experiments on how far LOP I could go and see what the speeds did.

Lucky I did not include a high altitude WOTLOP mag check in that lot! :E

hey whatever you do, do not post a link to this in the Private Flying Forum, you may start a war......and besides, I may want to save this little gem for a later posting!

A kiwi or two might know what I mean :E

Do you think that perhaps you have answered your own query??

Shock cooling can and will damage a piston engine very rapidly under the right conditions, or wrong conditions.

Try carting a ton of fertiliser for a climb of maybe 2,000ft, max continuous power, relatively slow speed, sow the load, pull the pwer and descend rapidly back to the strip. Do this maybe 10 times an hour, for maybe 10 hour flight time day and you will soon find that shock cooling is not an old wives tale.

When I first started in Aerial Ag work, as loader driver, heard an FU24 with 300hp flat six coming up the strip sounding like an old chaff cutter,
Stopped the ops till the cowls were lifted and engine inspected, three blown plug inserts, big cracks, engineers put it down to shock cooling.

This was fifty years ago, no where near the engine instrumentation available then as is now, but if there was it would no doubt have shown just how hard these engines were worked, and would have shown, as most of us learned quite rapidly, leave a bit of power on during the descent.

So my question would be... sure, the engineers may have put it down to shock cooling... but what ACTUALLY caused it?

Back in the day, with no hard data, it was pretty normal to blame failures on mis-handling, whether it actually was or not. Many engine shops would blame any failure of one of their engines on the pilot, and "shock-cooling" was a pretty common charge.

Back when I was younger I used to race motocross bikes, and it always used to make me wonder why my two stroke motor, operating pretty much on the edge of seizing for most of the race, could endure being occasionally dunked in freezing water without ill effect... because that really IS shock-cooling...

Would be pretty interesting to see something like this done on a C206 or C182 doing parachute ops, only obvious difference I can see if on a real hot day with the engine struggling to take a full load all the way to say 14,000ft then dropping and descending say 2,500 - 3,000 fpm, i'd imagine this would be somewhat different!! Not to mention, as prospector said, doing it up to a dozen times a day.

BUT, IMHO, you're probably right about it being hard to shock cool an already cool engine!! Most of the decent drop pilots i've known had taught me the real trick is to start letting those temps come down as soon as you're at top of climb before you start descending, that means getting the power back to just above what you need, start getting a bit of extra mixture in, cowl flaps open etc...etc...

If memory serves me right, we were told to never exceed -13 on descent (Thats 13degrees per minute on the CHT, determined using a JPI Gauge), but my memory on those numbers is a little fuzzy now!!

Shock cooling caused it, from a hard climb with temps on top limit, to a high speed descent with no power does cause shock cooling.

Engineers who were responsible for fleets of up to 20 aircraft or more sould see a pattern Th aircxraft operating in locations with a long hard climb to sowing area and then a high speed descent saw a lot more cracked cylinders, plug inserts than those aircraft operating in kinder country.

Perhaps because they are two entirely different engine types, different metal masses etc.

Hmmm \, interesting one this, there is no doubt (is there?) that if you heated a cylinder to, say 350- 400 degrees and shoved it in a bucket of cold water, cracking would be possible, if not likely, however, if you shove it into air, what then? My experience leads me to believe that not much will happen except the cylinder will get cool at a fairly even rate. On the other hand, I have heard of many glider tugs that have cracked cylinders from descending too rapidly, or indeed, is this the reason that glider tugs seem to suffer an unusually high incidence of cracked cylinders? Hmmmm?:confused:

Actually Jabba what you have shown us with your graph is that your cylinders were not shock cooled, had you done that let me assure you that they would have cracked.

They are... the two-stroke engine being far more powerful for a given displacement, and, when in racing tune, running on the ragged edge of destruction every race... with very tight tolerances when operating like that. Throw less than perfect lubrication into the mix... you would have thought that the racing engine, particularly with it's low mass and therefore greater susceptibility to temperature change by sudden immersion in cold water, would be far more prone to failure... but they aren't.

Anyway, hard to argue with traditional wisdom... lol

And back at ya :ok:

Say hello to the bigger Jnr!

Quite an interesting bit of data from some pretty nifty monitoring gear (gotta love technology!), but to play a bit of devils advocate here, statistically speaking the data means nothing as it isn't repeated and we have only one sample. One could easily say that the engine held up well because it was handled properly over time so held up well with a little bit of "tough love".

I would really like to see how this graph (sample 1 if you may) holds up if you repeat this over a period of time.

I'd also love to see how the graphs would compare to super or turbocharged engines.

I'm by no means discounting (or rubbishing your theory for that matter), your monitoring equipment provides some some fantastic insights in to what is happening inside the engine and gives us possible insights in to debunking a wives tale, but lets not get ahead of ourselves, I'm sure you would not get a great reception from any of your mates who own a radial engined plane if you pulled the throttle back to the stops and pointed the nose down at the ground with the assurance of "I tried this once and the graph showed it was fine" :E

Again, just playing devils advocate.

Lots of old wives tales in aviation. Continental's seem more prone to cracking and warming up issues than Lycoming.
The more lives a cylinder has the more chance of cracking. Cylinder cracks seem less prevalent these days, people tend to put new cylinders on and I think that is part of it. The old days it wasn't unusual to have 4 or 5 lives of a cylinder before it was junked. The days Prospector was talking about the Flitchers used to have Continentals in and they had to run flat stick to get anywhere. I'm sure it was put down to shock cooling when a cylinder finally gave up the ghost after 5 or 6 thousand hours.
To talk radial folklore you have to be a deaf, dried up old fart with piles. Plenty on here like that so lets hear the old wives tales about radials. :8

I have a bit of experience with this.

At my last 100 hourly check on my plane with a Lycoming O-320-E1A engine three of the cylinders had fine cracks near the exhaust valve.

The fourth cylinder had a crack aluminium welded about 400 hours ago.

As I do a lot of aerobatics in the plane I thought the problem was shock cooling

When I checked the maintenance documentation I found that the cylinders manufactured in 1971) had 3,100 hours on them, including a 10 thou overbore at 2,000 hours done about 20 years ago.

Interestingly, the Lycoming documentation said the cylinders are good for 3,000, which means they made their estimated service life.

The most economical fix was to buy four new complete Lycoming cylinder kits, which include new cylinders, pistons, valves etc. It cost the same to switch to higher compression pistons, so these were installed under an Engineering Order and I picked up an extra 10 HP. Each cylinder kit cost about $1,300.

Bottom line is that cylinders do fail, but think that it is possibly people worry too much about shock cooling and that the problem is over stated.

prospector
No, not really, I never had the question. However you read all sorts of threads on prune, some not in D&G which are less well informed, and folk spruik on with all manner of old wives tales, and the punters reading believe it. So facts and data are pretty good to see, and very few actually get to see it. I am fortunate, not just in what I see on my own EMS but from other sources, so it is only fair to share good facts and data when they come along.

I sent this data file complete to Mr Deakin and co as well, JD was delighted with all the other data that you just don't get from a JPI. So why not share it here. His reply started with "we're convinced :)" so I figure that was good enough!

Getting onto your anecdotal story, and I do not mean that in a derogatory manner, as I believe you when you say what you saw and was told. However as remoak has pointed out already that has always been the "claim from the mechanics".

I did refer to John Deakins articles of years gone by, and while he rightly says that getting an engine REALLY Hot, and then diving at the ground, may have some negative effect, and possibly the ag ops you refer to could be less than optimal for an nine, the vast majority of flying does not involve this.

Lets look at the scenario you describe.
> Ag plane, rough and ready, but perhaps with poor baffles and maybe fuel delivery. Without proper instrumentation you would never know.
>Climb out temps, and operating temps. Again you would never know, and it is my opinion only that this is where the damage was done. It is the opinion of others as well. but again, no data to prove one way for sure.

If the cycles of shock cooling were real, why do so many flying school aircraft not suffer from it? And they are all operated sub optimal.

I think it was most likely, given the vast data and knowledge that we have today, that the genuine observations of your ag engineers of yesteryear while valid were misguided into believing the descent was to blame. Knowing what we know now, and seeing lots of good data, it is most likely what you describe was the takeoff and delivery phase.

So maybe it involves a rethink to dropping/glider ops in order to extend life.

It is a bit like the exhaust valve failures of TCM's for the last 10-15 years, all blamed on LOP operations, even when some engines never ever went LOP. It was never about mixture and all about the reaming of the valve guides and accuracy of the fit of valve to seat.

nitey nite! :)

prospector

SHOW ME THE DATA

Wannabe biggles..... some radials have different issues, nothing to do with cooling so please do not confuse the issues :ok:

facts and data........Wannabebiggles aid about repeated data.......come on mate, John Deakin has been writing about this stuff for 10-15 years. His data has come from not just an amazing career in pitons (flat and radial) and jets but also from being involved as an unpaid test customer of GAMI/TAT and involved in the only decent pilot education program on the planet.

So this i just Jaba proving many many many years of other proven science, by those approved to test and those who do FAA approved testing. This is no way a java revelation. Just proving known facts, and those still surrounded in folklore myths (OWT's).

Hey ranga

DOGIES!!!!!!!!! \\\\ ////

Anecdotal evidence...but from a reliable source

This was from the USA, and in response to my data, just saying...... :ok:

From reading John Deakin's articles on engine handling and so called shock cooling, I realise he has done a great deal of high class research on the subject. On the other hand almost all the LAME's I have met over many years have a huge variety of personal opinions on engine handling invariably gleaned from their apprentice days from their teachers - who passed it on from their teachers who were LAME's and so on.

LAME's and their ilk may know how to tear down and build up engines and fix things but the majority do not conduct further in-depth reading once they have their licence. Therefore to say "engineers put it down to shock cooling" means nothing since they are personal opinions and not hard measured data.
While I listen what an LAME has to say, I also treat his opinion on engine handling with great reservations knowing it is a personal opinion only.

Jabawocky, could it not also be that in that Quote you posted, its as I was saying, its hard to do if you're taking care of the engine and doing the right things?

Obviously I think everyone can agree that Shock Cooling is a real possibility, but it seems (Keep in mind this is based on my own relatively low experience and the data from your graph) that it would mostly be caused by poorly managed engines and perhaps those with higher T/Os and LDGs cycles operated in hotter climates?

I've always wondered somewhat about the relationship between Dropships going up to say 10,000ft or more and the positives that the cooler air up there have on the engine in respect to Shock Cooling. Wouldn't it be fair to say that as you get higher that the cooler temperatures can help the engine from getting as hot as one operated lower and then, when on Jump Run, as the power is brought back, with the cowls open and the nose brought down the effects of being nice and high would allow the engine to cool somewhat before you even begin your descent?

I always remembered the worst part of any hot day was the first 5,000ft or so with the aircraft at gross and watching all the temps get waaayy waaaayyyy waaaaaayyyyyy up the dials, after that though you were usually free and clear!

I think its operation type dependant. Having a a gliding background, i've seen plenty of cracked cylinders.

Tug ops would have to be the worst environment. its full noise to TOC (normally 2000') normally at 60 knots. then power off and nose down for a stuka descent.

Looking at jaba's data and thinking about the other ops, most of them have a period where they are running at a lower power level.

Even meatbombers run for a period that full power is not being used. Looking at Jaba's data, the run into the drop appears to be enough time to drop the CHT's back to cruise levels.

Someone mentioned training aircraft doing laps. Same would apply as PJ ops. The run on downwind at less than full power, is enough to lower the temps to an acceptable range. And if you think about it truly, in a warrior, turning base you drop the power to 1700 rpm, which means you are still generating power/heat. Rethinking it a lil, it might not be as critical as PJ ops, as the climb is shorter so the chance of reaching max CHT lowers.


I relate this whole thread back to the one we had about turbo charger cool down.
In this case, for most operation types, it's an old OWT, however in an operation like glider tugging, it is a very real threat, and one that needs carefull management.

You are on the right path here.

And this next bit taken as a whole only applies to naturally aspirated,
The thing to remember, is that the by product of power production, is heat. So as you climb past Full throttle height, the amount of heat you are capable of generating lessens. Then you add in the fact you pointed out the air is cooler. So heading towards the top of climb, things are working in your favour (except climb rate). Even the best jump pilots will have 30-60 seconds of run into the drop at a reduced power level. Yes its cooling, but not at a prodigous rate, as 1. the engine is still producing power, slowing the cooling rate, and 2, still at a slow airspeed, so cold air is not being rammed through the baffles. Using jaba's graph as a guide, i wouldn't expect a jump engine to be much hotter than normal cruise once he points the nose at the ground, and CLOSES the cowl flaps to keep the heat in.

That might be where you need to use your head, lower the nose a lil, gain an extra 5 knots to make the owner a lil happier.

IXILY and Jaz

I think if you mean getting an engine up to 475F or something stupid, and then doing a dive, it may be possible. However I doubt from basic engineering understanding that the Delta T can still exceed something reasonable. I have not tried it, but I can assure you a few of the known "guru" folk do not see it being reasonable. You will have to trust me on that one.

If you dive at twice the rate, say 4-5K FPM will you double the cooling rate? how about square the rate? It is still bugger all. It is still less than the heat up rate, or the after shut down rate.

It is like the turbo cooling debate, everyone with an pinion has never stuck multiple thermocouples to a turbo and done it. The one group who have have a bunch of data that proves the old myths are full of BS. Unless you have data to prove the other data wrong, well its just an opinion.

Meat bombers do have a period of transition, even they can't do engine suicide, otherwise the grass darts would not get out!

i'm with you jaba,

was on the turbo debate also.........

Of i was to put my position down, i'd say in short.

1) in general operations, operating within the manufacturers guidlines, shock cooling is pretty much impossible.

2) operations like glider towing do present a risk of shock cooling. No manufacturer offers guidlines on engine management for this type of operation, so everything done, is based on OWT's, and the very real and frequent cylinder cracking that occurs.

I always used 380 dgrs as a top limit in the climb and did not usually lean below around 5000ft depending on the day. Regardless until level on jump run it was not below 18 gph at 12000 ft, I would lean it more before descent, close cowl flaps etc temps now in low 300s dgrs.

Also at WOT and full rich at the start of the climb I liked the fuel flow on the red line, to me this was minimum, not maximum. The only trouble I ever had with cylinders was sometimes having to relap exhaust valves. I always had factory remans rather than rebuilds, mainly to save time.

I did use LOP on any cruise flights, going to maintenance etc, and it worked very well, just as advertised.

You guys all seem to believe the wives tale that your fancy gauges have their probes in exactly the right position for all enviroments and that cylinders have equal temps across them.:ugh:
With a bit of intelligent operation shock cooling should not happen, but nothing is fool-proof.:E

Interesting as always Jaba, thanks.

Yours isn't bad either :ok:

Sorry cannot do that, the technology was not available at that time. What was known was that some pilots were very good at cracking cylinders and some never did. It had to do with the operating environment ie Some area's had an hourly charge out rate, and some charged ton/mile. Some had long hard climb at max temps followed by power off descent.

On the hourly rate the farmer was often cracking the whip for the fastest job, on the ton mile rate the Company kept a very close eye on times, so the power off high speed descent was an easy way to save a few minutes, but was hard on cylinders.

As has been stated by Glider tug and parachute operators the problem was much alleviated when a trickle of power was left on for the descent.

Perhaps if the problem of cracking cylinders in these type operations was referred to as thermal cycling rather than shock cooling it would be more accurate.

A good example would be the Lycoming IO720 when used in the agricultural role had a TBO of around 1,500 hrs.

The same engine used in a Queenair regularly flying 2:30 legs we got the TBO up to 2,400 hrs.

Yes I think this is closer.

Some years ago I spent some time with a technical representative from Teledyne Continental in respect to a court case that involved cracked cylinders on a couple of TSIO-520s. The matter involved a dispute where one party was arguing the cylinder cracking was caused by the operator and the other party was arguing the cracking was caused by fatigue (despite the engines only having about 300 hours time since new).

The cylinders are made up of a number of different metals with different expansion rates, (aluminium alloy heads, steel barrels, steel valves, steel spark plugs, steel studs & inserts, bronze valve guides and stainless or inconel exhausts etc).... these all expand and contract at different rates as a result experience considerable stress during rapid temperature changes.

If you rapidly apply full power to a cold engine or cut the power to hot engine and allow it to rapidly cool as would occur after TOD before a high speed descent the amount of stress over a period of time will cause the cylinders to crack.

On the IO-520 and TSIO-520s one of the weakest points is between the upper spark plug insert and the fuel injector port. If repeated rapid engine cooling occurs, the alloy cylinder head will cool much quicker as a result of the cylinder cooling fins dissipating the heat much more quickly than other parts of the head such as the steel spark plugs... as a result the hotter plug causes considerable stress on the now cooler (and shrinking) plug hole... over time the stress is released by cracking from the plug hole (often towards the injector)

A similar thing occurs on the 360 Lycomings where you will get cracking in the exhaust port emanating from stress around the valve guide and seat.

Another example was on the TSIO-520s, in aircraft like the C402, where repeated rapidly applying full power on take off without warming up the engines properly would likely manifest itself by the alloy cylinder head separating from the steel cylinder barrel. This is because the alloy head and combustion chamber heat up far more quickly that the barrel... the end result is cracking and eventual separation between the head and barrel.

Good engine warm up, smooth application of power, smooth reduction of power and good temperature management will result in far fewer engine problems including cracked cylinders and wear, particularly older manufactured engines where the manufacturing process resulted in metal that is not quite a strong.

As for parachute & glider ops, we worked out years ago by slowly pulling of the power prior to drop or release, and carrying some power on descent until slowed up on final approach, exerted far less stress on the engines.

I wish I still had the Continental report from the court case, but it was a beautifully written technical document that said the operator was a hamfisted mug!!

i have heated quite complex aluminium/steel/titanium aircraft fittings/casting and forgings to well over 500degC for quite a few hrs, then dunked them in room temperature water..

never had one crack.. (shock cooling in manufacture tends to create a part thats more resistant to cracking)


is it possible that cylinder cracking might be caused by incorrect torque down procedures? ill fitting/re-used gaskets?.

Uniform heating shouldn't introduce unwanted internal stresses in a properly designed component.
The thermal gradient (and number of cycles) within the cylinder itself are the primary causes of thermal fatigue problems, at least as I was taught.
Using reworked cylinders seems to set one up for these sort of problems.

Jaba, really interesting data in the graphs. Thank you for posting. Probably the most interesting stuff I've seen on here for ages.
Just a couple of questions if I may be so bold.
In accordance with your statement Can you confirm that
One minute after TOD as you passed 11,000 ft with a MAP of 15.3 inches and a Fuel Flow of 32 Litres/Hour the throttle was at Idle?
The MAP increases to 16.4 inches over the next 3 minutes as you approach 9,000 ft at which time the MAP drops to 13.6 inches.
The MAP then increases once again to 14.2 inches over the next minute as you pass through 8,000 ft and it seems that an idle MAP (MAP drops to 8.5 inches) is indicated as you passed 6,400 ft @14.37 (MAP drops to 8.5 inches) until you reach 2,800ft at 14.39, indicating that twice or (perhaps only once with the RPM increase) that the throttle was reduced again.
The delta T from 13k down to 6,400 ft on cylinder #1 was a modest 26 Degree F. However the Delta T from 6,400ft to 2,800ft on that cylinder was 39 degrees F. coinciding with the 8.5 inch MAP.
It seems to me that the data shows (by the step increases in MAP as air density increases on descent, that the engine wasn't fully at idle until passing 6,400ft).
I'm just a poor layman trying to interpret that awesome data graph.
I find the info you provided fascinating. Well done.

Do note this is a Lycoming, and not a Cuntinental who seem to have much bigger issues with this.

Anyone like to comment on using TAS not IAS for VNE ?

In cruise, roughly what % power you using? Something like 65%
I noticed 18.5 MP / 2450 RPM in cruise. Why use climb RPM? just curious, not saying it is bad, just trying to learn other reasoning?

What is "Pitch" on the graph?

Fantastic graph by the way.

It seems that they build engines better these days. I have long suspected that many of the failures of the past have been down to the fact that while the basic design was right, the manufacturing of the engine was so poor.

From FLYING APR 2012
Improvements in modern reciprocating engine production all start with the switch-over to more modern machining, which can cut metal to incredibly close tolerances. This means that a Continental, Lycoming or Rotax engine built today is a physically better aircraft engine than has ever been mass-produced. You might recall that Continental at one point offered a Platinum-series engine that cost more to buy but had tighter tolerances and therefore a longer warranty. With improvements in machining — including a change to automated manufacturing processes — all the engines Continental builds today meet or exceed the Platinum specifications, and so the special line has been discontinued.

The shock cooling debate has been a fixture of operating piston engines for a good long time. I think care has to be taken in out and out rubbishing "old wives" tales. Many reflect opinions that are reflective of a lot of practical experience as well as the innate conservatism of an endeavor where the penalty for getting it wrong can be unforgiving.

That been said my 02 cents are as follows

1) Understanding the effect the mixture has on engine temps is IMO generally rather poor for GA operations. In particular I just cringe when I see the mixture jammed full rich prior to the start of the descent, particularly on cool days.

2) Flying the airplane comes first. Ya do what Ya gotta do. If that means a rapid power reduction because you got held up close and high well then that is what you do.

3) Despite point 2 in general my feeling is that piston engines have a lot of hot parts moving at high speed. It would seem to me that "gentle" handling of the engine, that is slow and smooth power changes and in particular a slow reduction in power as the airplane descends will make life easier for the engine

4) I think care must be taken in interpreting EMS data. The only temperature that is measured is that at the probe. I am not sure you can automatically assume you have the entire picture of what is happening at every part of the cylinder. That been said EMS data is still extremely useful particularly in diagnosing engine faults earlier enough to prevent damage.

Well, one thing is for sure... this thread is a very good reason why the ancient design of most common aircraft engines should be dumped in favour of a good, reliable turbine! Try shock-cooling that sucker... it will just laugh in your face and carry on regardless... :ok: