I was flying today. The air temp was a balmy -4 degrees F at the surface….Neg 10 at altitude. Farking cold for the preflight, especially when I spilled avgas all over my hand.
The flight instructor warmed me on taxi to “be careful and make sure my power adjustments, especially power reductions, were done slowly and smoothly so as to prevent “shock cooling” of the engine”. (ETA: Apparently “shock cooling” causes issues with the heads and cylinders…cracking and/or other structural issues)
Now, as I said, I am not an aviation powerplant engineer, nor any sort of powerplant engineer…..I have, however, an engineering degree, and I have lots of thermal management experience under my belt….further, I used to service all sorts of air cooled small engines when I was in college for rent money.
Therefore the theory of “Shock Cooling” an aviation engine simply by closing the throttle quickly sounds fishy to me. Shutting down an already overheated powerplant? Maybe. Immersing it in water (or filling the cowling with a firehose?) maybe…but probably not. But a gas engine that is still running should not be able to be cooled fast enough to damage it simply by slowing down the engine. What happens to an engine in flight when the airplane flies through a rain shower? Mist? heavy rain? snow? All these should lead to significant cooling of the engine in a very short time. Water conducts heat better, plus evaporation. Faster cooling. Yet I don’t hear of Lycomings or Continentals (or Rotaxes (Rotaxi?)) suddenly shedding cylinders or valves because of rain.
I would think shutting the engine off after use would do more damage (due to sudden changes in cooling vs heat) than closing the throttle suddenly. Or unloading the prop with quick attitude changes (say climb to level to dive)….And, of course, the sudden dimensional changes in temp due to starting the engine at all……
Again: not an aviation powerplant expert. But have more experience than most on thermal issues.
Does anyone with real knowledge have some input? Is there something to it, or izzit just some myth carried forward by folks who are pilots but not engineers?