I do some driving in and across the Sierra Nevada mountains in California, so I'll offer this example. Climbing, and using boost, I want to pull into a turn-out for a scenic photo. I'd leave the engine running. If I was on a long down grade and wanted to stop for a photo, I'd shut off the engine. If I were stopping for lunch on the upgrade, I'd let the engine cool for 2 or 3 minutes. It's hard to believe how hot the exhaust manifold, turbo (hot section), and exhaust headpipe get on a long grade.
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