Car engines i am sure have the same shock cooling, why is it a problem for aircraft engines,
As Tinstaafl mentions, car engines are liquid cooled. The cooling air flows over the radiator, rather than the engine. The engine maintains a much more uniform temperature throughout, and that temperature changes much less quickly when conditions change. If something shock cools, it would be the rad, not the engine. This is a happy characteristic of liquid cooled aircraft engines. Having done 64 three minute climbs these past four days, in a DA42, with the required descent following each climb, I was delighted that the liquid cooling allowed somewhat more rapid power changes.
I always understood Lycosaur-powered planes have them, and proper technique includes closing them during descent (sic!) for the exact reason of avoiding, or at least reducing, shock cooling?
Yes, if you have cowl flaps, their proper use it very important. Any aircraft which has cowl flaps will also have a cylinder head temperature indicator. As mentioned by Big Pistons, some lower powered aircraft engines are less sensitive to shock cooling, and thus do not have cowl flaps. It is still and excellent habit to treat those engines similarly gently with power changes. It is still better for the engine, and forms a good habit, which will be reassuring to the check pilot when you are hoping they will sign you off in the bigger engine plane. That said, I have see cracked O-200 cylinders...