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by ledauphin 1274 days ago
sure, but the basic physics at the very heart of the issue (use oil to avoid direct contact between metal pieces) is exactly the same.

it seems very unlikely that modern refinements have completely reversed the concerns.

1 comments

Having a water jacket around the cylinder makes it less possible for the cylinder to heat (and change size) unevenly versus an air(/oil)-cooled engine. That same water jacket permits the tolerances to be set to assume a maximum head temp under 300°F (versus 460°F for airplanes). That means the steel rings don’t have to deal with as much dissimilar expansion as the aluminum heads and pistons. This allows engineers to choose tolerances accordingly. It’s not so much modern metallurgy or electronic controls, but a factor of having a lower temperature range.
I don't see how water jackets, pistons rings, and their tolerances are directly relevant here. The topic was bearings, and their lubrication and wear, in the larger context of warming up your car before driving in cold weather.
Imagine a cold-soaked engine with an aluminum piston, steel rings, a cast iron sleeve in an aluminum head. The aluminum piston will heat very quickly compared to the cast iron sleeve in an air-cooled engine. (There’s a massive aluminum heat sink in the form of the cylinder head.)

For a water cooled engine, there is a water passage around 3/16” from the cylinder wall which helps to bring the cylinder up to an even temperature more quickly and prevents a high heat flux from expanding the piston to the point where it can scuff the walls.

It’s not only oil pressure that is a concern for a cold-start to operating temps.