[Tannaton]

The issue with Semi Synth is mainly in Turbocharged engines where the oil is exposed to much higher temperatures. The mineral base is prone to "cooking" and leaving deposits that restrict or block oilways which can kill turbo's and top ends.

Petrol cars run at higher temperatures but the turbo's are usually water cooled. On diesel turbos most rely only on oil cooling for the bearings so the slippery stuff doesn't necessarily get an easier life.

Semi Synth is fine in most non-turbo engines.