Are Synthetics Superior?

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From the book Synthetic Lubricants and High Performance Functional Fluids

The performance benefits demonstrated by the various tests that have been described are meaningful to the automotive engineer or tribologist, but the average consumer is most interested in how much savings the use of a PAO-based product is going to generate.
This case describes the results of one study that considered both the increased fuel economy and the extended oil drain interval made possible with part- and full-synthetic PAO crankcase oils. The original calculations have been updated to reflect current prices for gasoline and oil in North America. The calculations are based on 15,000 miles of driving and a “do-it-yourself” oil change regimen. A pump price of $1.20/gal for gasoline has been chosen, and the oil has been priced at $1, $2, and $4/qt for the mineral oil, the part-synthetic, and the full-synthetic, respectively. If the oil is changed every 5,000 miles, there is almost no cost differential for the three oils because of the improved fuel economy gained with the synthetics. For the 15,000 mile distance, the savings over the mineral oil formulation is $3 with the part-synthetic oil, and a deficit of $3 is experienced with the full synthetic. If, however, there is only one drain for the full synthetic, the savings goes up to $11. In Europe, where gasoline is much more expensive and the differential in oil prices is less, the savings accrued by the use of synthetic crankcase oils will be much greater.

The use of lighter grades of crankcase oil is one answer to the need for increased fuel economy. The possible downside to this strategy would be a concurrent increase in oil consumption and the loss of sufficient high temperature viscosity for adequate engine protection. Studies show, however, that properly formulated PAO-based synthetic crankcase oils, with wide multigrade SAE performance classifications, can outperform mineral oil based formulations in both fuel and oil consumption, while maintaining superior engine protection.