I've been considering using AMSOIL at the next oil changer. I have a 1993 940 turbo. Is synthetic AMSOIL harmful to this engine? 480,000 miles, still running smoothly 750 to 800 at idle.

 

Amsoil is just a brand of synthetic oil. Synthetic oils are created from natural gas so they don't contain the random sulfer and long chain molecules that remain from the cracking process of dino oil, so in that sense its purer oil. The only thing to worry about is that its actually slipperier and can find its way out through old crusty seals, particularly on a car who's PCV system isn't in good shape. What I'd recommend is going to a high mileage oil that has seal softeners - maybe even consider a synthetic blend high mileage formula from top brands like Valvoline or Pennzoil, which you can find at Walmart for a fair price. PS - I don't see any value to using a more expensive boutique motor oil on a high mileage car - any damage/wear is already there and its not like using a traditional motor oil will speed up the wear. Just change it at the recommended interval using an OEM quality filter (I buy Mann filters in bulk from FCP). Stay away from Fram and other brands designed for low revving American cars... If you try the blend with seal softeners and don't see any weeping, then you may try a full synthetic high mileage oil - but again there's no huge upside for your car and you're paying a premium price.