I am in the don’t believe camp. I am not looking to persuade, I just offer a few anecdotes that have informed my opinion. My TB 20 has been abused in IR training for 5 years. No consideration at all is given to shock cooling. Some effort is made to keep No 4 cylinder below 400 so we do reduce power in the climb. Cardiff love the slam dunk ILS from FL80 so maintaining 900 ft a minute for 4 or 5 minutes is far from unknown. We have an analyser, oil analysis, cut filters etc and no evidence of issues. I think our students have far more important matters to concern them even though I am paying all the bills. There was mention of IO 320 data. I have a PA 30 and am chasing fueling issues so am anal at the moment with full monitoring. I second sample rate from EDM 960, Savvy analysis, filter cuts, oil analysis at Blackstone. Its a manual turbo but to be fair I don’t use the turbo much. I have no cracking issues but top overhauled one engine due to valve guide wear.
I have owned about 12 different aircraft and the only serious cylinder issues involved a cylinder separation on a small nearly new Lycoming where you could actually lift the top off and on a mid life IO 520 a crack so large that the gasses torched the fins on the adjoining cylinder.
My view is that at various times cylinder manufacture was poor quality, often due to outsourcing. Continental has in general bigger engines which are inherently likely to have bigger problems but sometime Lycoming made special efforts to be as bad. I feel manufacturing quality and cylinder age is more of an issue than shock cooling.
As regards better engines I have flown a few hours behind the water cooled Continental and liked it. Performance in the Extra 400 was better in some respects than the same airframe with an Allison Turboprop. This was not Continentals first effort at lateral thinking. I owned a Robin Tiara with the Continental engine that drove the prop with the camshaft to provide gearing.That could have been a great engine with a little development but unless an engine goes in a volume production airframe it stands little chance.
Regarding rain, I have a data point from a flight today: the CHT variation, at FL080, +3C, 150kt TAS, between no rain and heavy rain, is around 15F on the front two cylinders, and around 10F on the other four.
I agree; I can go down at -1000fpm too and not have a problem. But I always keep some combustion going.
Funnily enough on the TB20 the hotter ones are on the right – presumably because the oil cooler is stealing some air on that side 
Bonanzas tend to have hotter left engine sides, for various reasons, so I sometimes have CHTs of 390-400°F, especially #4, in climb and cruise. But I never observed the kind of cooling apparently necessary to see shock cooling. Not in any way if I descend normally, at 500 fpm – but even if ATC gives me a >1200 fpm descent (with flaps and gear down), I still try to keep enough power and combustion to keep the cylinders warm… However, if I would reduce the power to zero, for a longer time, I guess it would strain the engine, especially in winter when OAT is below zero.
I really believe that as long as there is some combustion going inside the cylinder, the airflow alone cannot possibly bring down the temp that much to cause any problems. As was said before, airflow around the cylinders only accounts for about 12% of CHT.
In a PA28 or C172 though, with fixed gear, I imagine it is somewhat ‘easier’ to reduce the power to zero in order to descend quickly, and if its very cold outside, I can (at least theoretically) imagine an issue. Not if there is no combustion at all going inside the cylinder.
Shock cooling damage is an expensive risk to aircooled Lycoming and Continental engines. The operating technique will greatly effect this risk. A Lycoming or Continental engine with cylinder head cracks resulting from careless operation with respect to cooling will continue to run, but will not be airworthy. Repair will be expensive (compared to not having to repair it), and the repair risks other damage (pulled studs) to the engine. If the owner chooses to not maintain the engine as airworthy, and runs with cracks, it’ll run for a while yet, with less power output, and more risk that the cylinders will crack more, and break apart.
If the engine were used at lower power demands, risks of continued cracks are much less. If the engine is run at a very constant low power demand, with constant cooling, it will be much less vulnerable to shock cooling damage. And just about every other type and application of gasoline engine is either much less vulnerable, or immune to shock cooling damage. That doesn’t mean we should operate them abusively, but there is less risk. So any other liquid cooled engine, and fan cooled air cooled engines cannot be compared to GA airplane engines.
It’s easier to operate the airplane engine with care, than to present examples as to why it’s not necessary – it still is….
At 20% power of course. At 65%+ not so much. Having previously run a 52TW I can guarantee you that a M14 will run nowhere near 20k in aviation usage. Be happy if you get 500 out of it.
20% power even a Lycoming will last 20k hours.
None of them will ever last like the CD series do.
A Ukrainian friend says that when removed from e.g. the Yak 52 family, Vedeneyev M14P engines are used as well head water pumps in remote areas and last for 20,000+ hours before failure. Russia and central Asia are about as remote as it gets, so they must be more reliable and easier to work on than modern ‘efficient’ engines which I would surmise are from the automotive industry.
There was a poster here years ago who ran a pleasure boat business in Africa and he said the Volvo engines used in them were of appallingly bad quality. He was constantly repairing/replacing them.
Peter wrote:
Never heard of cracks in a new engine. It would be outrageous.
Haven’t said that. I was actually referring to engines in boats that have a similar usage profile to aircraft engines (operation under constant high % of power for longer periods of time) but are cooled differently and therefore the aircraft type shock cooling can’t happen.
If it is true that shock cooling is a major driver for such cracks, one would expect that such engines have significantly less of them…
Malibuflyer wrote:
So many reasons: High temperatures, mechanical stress, vibrations.
Perhaps. Though the pilot has direct control over the care they take operating the engine, and to some degree, high temperatures. Mechanical stresses and vibrations are much more design and maintenance concerns. The pilot should be aware of obvious changes in maintenance condition of the engine, but short of massive abuse, can’t really affect these factors much.
Malibuflyer wrote:
One can find cracks in engines that have never been shock cooled – even never been in an airplane!
If you’re finding a crack in an engine which has never been in a plane, there are certainly quality control and maintenance concerns about that engine – again, outside a pilot’s control. If it’s not been in a plane, a pilot has not mishandled it!
I’m struggling to understand how it could be asserted that cracks, typical of those caused by shock cooling, could be determined to not be from shock cooling.
Bobo wrote:
How about flying through a hefty rainshower? I never watched CHT’s in the rain,
Generally, the part of the cylinder head vulnerable to cracking is not directly exposed to free flow rain in flight. A half portion of the cylinder barrels, and lower portion of the heads cooling fins are commonly exposed. Though I’m not a thermal expert, I expect that the thermal energy of water drops is very little compared to the heat being radiated by the cylinders – it just boils the water off.
Few things are perfect, and even with care, cylinders may crack. The point is that with engine handling care, cylinder cracking can be greatly reduced, so why not do that?
