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Dummies Guide to diesel engine oil

Dummies Guide to diesel engine oil

My recent trip to watch an engine teardown in Greensborough taught me a lot about oil. In order to cover the topic I had to do a little research before and after I wrote the Shell Rotella piece on its new experimental oil it says will be the wave of the future. Here’s a cheat sheet to the acronym-rich terminology of engine oil and the new PC-11 category you’ll need to study up on when it hits the market in the next year or two.


  1. PC-11: Stands for Proposed Category (PC) 11, a new category of engine oil that is low-viscosity (see def.) and more heat-resistant than the current engine oil on the market to handle the extra 10C in heat produced by the new Tier 4 engine technology for reduced emissions. The big benefit of this oil for buyers? Increased fuel economy without sacrificing durability.
  2. CJ-4: The current category of diesel engine oil that has been around for 10 years and will soon be replaced by PC-11.
  3. Viscosity: Basically means the thickness of the oil. Which flows faster? Honey or water?
  4. Fluidity: The reciprocal of viscosity, usually symbolized by φ = 1 / μ or F = 1 / μ, depending on the convention used. (Thanks a lot Wikipedia. Now it’s suddenly clear.)
  5. HTHS: High temperature high shear. Type of oil that improves fuel economy and durability of an engine.
  6. ASTM: American Society for Testing and Materials
  7. API: American Petroleum Institute
  8. HDDEO: Heavy Duty Diesel Engine Oil
  9. Shear stability: A measure of the amount of viscosity an oil may lose during operation. Oil experiences very high stresses in certain areas of the engine such as in the oil pump, cam shaft area , piston rings, and any other areas where two mating surface areas squeeze the oil film out momentarily . (Source: Bob The Oil Guy.)
  10. 10w30: Seriously, don’t even go there. It’s more complicated than you might think.

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