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Generally speaking, the lower the viscosity, the better the fuel economy of the engine. In formulating lower-viscosity oils, it has become clear that synthetics are the base stock of choice. This is because it is possible to produce a synthetic oil of a given low viscosity without incurring the excessive oil consumption (due to evaporation) and resultant thickening of the same low-viscosity petroleum oil. Indeed, the U.S. Department of Energy, in its pamphlet entitled “An Assessment Of The Effects Of Engine Lube Oils On Fuel Economy”, states: “It is evident that low-viscosity oils will help minimize engine friction losses in the prevalent hydrodynamic region and thereby achieve better fuel economy. In addition, such oils help to reduce friction during ambient (cold) start by increasing the oil
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"...oil flow furnishes up to 30% of an engine’s cooling requirements."
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flow rate to critical engine parts. However, low-viscosity engine oils, blended from conventional petroleum base stocks, may have problems with high oil consumption and engine wear. (unit during operation, and can surpass 650°F (!!!) during a short period immediately following engine shutdown…both figures far exceeding the thermal limits of petroleum oil. Synthetics, with their capacity to maintain proper (low) viscosity and lubricity under these high heat and stress conditions, and with their natural resistance to oxidation, have risen to the fore. It is also important to note that the high-temperature-stability properties of synthetics are designed primarily into the base-stock oil itself, rather than being achieved primarily with additives. The advantage with this approach is twofold:
(1) Additives, which may account for as much as 25% of the volume of a can of premium petroleum oil, by themselves have little or no lubricating properties per se. Thus the more the additive content in an oil, the less lubrication is available to the engine.
(2) Most additives tend to volatilize (evaporate) and deteriorate with heat and age and use, so that the overall effectiveness of the lubricant is significantly diminished within only a few thousand miles of driving.
It is also important to note that, contrary to what many take for granted, higher viscosity in and of itself does not translate into better engine protection. Extensive testing has shown the opposite to be in fact true. As long as a lower-viscosity oil is formulated to resist evaporation and provide high film strength, this lighter oil will actually deliver more complete protection to the engine parts, since its more rapid circulation delivers both better lubrication per se, and far better cooling characteristics…a critical advantage, given that oil flow furnishes up to 30% of an engine’s cooling requirements. Prior to the introduction of synthetics, however, the problem of evaporation (and the resultant thickening of the remaining oil) was addressed primarily by increasing viscosity. In short, don’t be concerned with the relatively lower viscosity ratings of some synthetics. Syn lubes are a whole new ball game
