Volume 2 Issue 1 - Lubrication

The ongoing march to achieve more technologically advanced engines continues and certainly the GM Duramax diesel engine exemplifies that quest. The race between GM and its would-be competition has benefited you and me: the improvement in all aspects of these diesel engines is easily quantifiable in terms of horsepower and torque as well as fuel efficiency and endurance. Recognizing how vastly improved these diesels are to their predecessors, it should not surprise anyone that advances in the lubricants for these engines have also facilitated quantum leaps in performance.

Any oil, properly rated for use in a high performance turbo-charged engine, is a remarkable lubricant regardless of the base oil used. In this article, I will compare synthetic diesel engine oil to petroleum diesel engine oil and draw some conclusions and make some recommendations. Previous Lube Notes have established fundamentals of lubrication and how oil is made, so if you haven’t read those, a review might be in order. I am writing this article assuming you have read the preceding articles.

Click here to see a summary of costs comparison for petroleum oil vs synthetic oil...

To start, we should compare several performance criteria for petroleum oil vs synthetic oil...

Thermal Stability

How well does the oil hold viscosity as temperature increases? This is reflected in the Viscosity Index (VI) rating, with a higher number indicating greater stability. Petroleum oils rarely exceed 100 on the Viscosity Index while some synthetics rate higher than 180. Oils that maintain rated viscosity – instead of thinning out at higher temperatures – perform better in your engine. Thin oil will reduce film strength and result in higher wear rates of critical engine parts.

> Thermal Stability Advantage: Strong for Synthetic Oil

Higher viscosity index (VI) liquids are less responsive to temperature extremes. At 0°F, the VI 95 petroleum oil is thicker (measured in centistokes, a dynamic measure of resistance-to-flow) than the synthetic oil with a VI of 150. On the hot side at 210°F, the VI 150 synthetic maintains viscosity better than the VI 95 petroleum oil that thins out more easily.

Temperature Range

What are the highest and lowest temperatures the oil can tolerate and still provide proper lubrication, during continuous or intermittent duty? This range is established by measuring the pour point (lowest temperature the oil will pour) and the highest temperature at which the oil can hold sufficient viscosity in order to provide lubrication. Chart Two demonstrates the superior performance of synthetic oil vs petroleum oil. Group III hydro-cracked synthetics are not on the graph and it is important to note that the Group III synthetics will have similar cold flow performance but significantly less high temperature performance compared to Polyalphaolefins (PAO). PAO and Dibasic Acid Esters are the primary chemicals used in engine and drive line oils. A strong temperature range is paramount to providing proper lubrication, especially in severe duty or extreme temperatures.

> Temperature Range Advantage: Very Strong for Synthetic Oil