Somebody might know more about this than I, but I have heard a few times that if your car is not run from the very beginning on synthetic, use of synthetic later in its life may not be cost-effective. The argument being that it will use more oil owing to less than optimal wear during its early life. The explanation I heard is that synthetic is more prone to leakage from wear.

I have no idea if that’s a factor in the behavior of my Chevy van - 5.0 L. It has 178K and lately smokes pretty badly briefly upon start up. I’ve been using synthetic for about a year. You can get a pretty good price on gallon containers from the well-known oil company Kirkland at Costco. I’ve been told that worn valve guides are likely the culprit. My mechanic buddy tells me I may as well just rebuild the heads if I’m going to try to tackle that.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K