ark@alice.UUCP (Andrew Koenig) (11/09/84)
I am far from being an expert on this stuff, but I'm pretty sure about the following things. First, a major part of the reason that oil should be changed is that high engine temperatures cause the oil to break down with time. Synthetics are more resistant to this breakdown, hence the longer change interval. Oil should not pick up many metallic particles -- they should be trapped by the filter. Piston airplane engines are broken in with oil that does not lubricate as well as that which is used after break-in. The purpose of this is to increase engine wear, so that the piston rings will seat properly. It is apparently impossible to manufacture cylinders whose inner surface is so smooth as to make this unnecessary. I wouldn't be surprised if this were true for cars, too.