The guy I bought my Bimmer from had been using Castrol Syntec (full synthetic) 5W-50 (?!?) since the car's birth, as that is what his garage recommended. This is one strong engine, at almost 250K. I thought, why not, I still use it, and change it at around 7K.

Can't say for sure if the syn. oil is a major part of that engine's healthy longevity or not. I have read, more than once, that if you're going to use it, it's best to use it from the git-go. A car with 50K on dino-oil, as the theory goes, has already gone past the tolerances that a good syn. oil would have maintained. So you're going to be leaking more expensive oil for little gain.

Again, I don't know how true this is, just food for thought.

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Te futueo et caballum tuum

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