I've seen semi-synthetics (blends) on the market for some time, but have not seen any literature as to the amount of syn/dino in the blends. Are they 10/90, 30/70 or 50/50? Certainly the type of synthetic base (polyol ester,) the amount of Polymeric thickeners(the stuff that breaks down at high temperature to form varnish in your engine) and quality of the dino base are all factors to consider. Anybody knowledgable about these blended synthetics? Roger

Synthetic oil

A lubricant produced by synthesis rather than by extraction or refinement, and as a result of the synthesis, the molecular structure can be precisely arranged to meet the manufacturers' criteria for high performance engines. Synthetic lubricants are manufactured from a number of differing chemical bases, and several classes of compounds have been developed to provide base stocks for commercial synthetic fluids. Synthetic fluids are knows a Polyalfaolefins (PAO), poly esters, poly alkaline glycols (PAG), silicones, silicate esters, phosphate esters, fluoro carbons, etc… Synthetics lubricants frequently satisfy special requirements such as non-flammability, thermal stability, resistance to oxidation and radiation much better than mineral oil products. Also the urgency to the concept of environmental responsibility has led to the increased development and need for functional fluids that are both biodegradable and low in toxicity. A mixture of mineral and synthetic base fluids is often used to formulate high performance lubricants

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Roger
1983 300CD 246k sold
1998 C230 52k
1980 450SL 75k needs AC
1999 Subaru Outback Ltd 43k