Saturday, November 29, 2008

Engine Oil

Since we covered filters, and I haven't posted anything in a while, I thought it a good time to cover some facts about engine oils. I know there are many opinions but again, what I'll state here is fact and you can make your own decision based off it. I also won't get into the synthetic vs petro based decide.

The most common questions I get asked is "can i run regular car oil", "why do i have to buy harley oil", and "can i run diesel oil like Rotella"? So here we go....

To first take it all in, we need to know what the API ratings on oil mean. So what do the API ratings mean? For starts, the "C" specification is for diesel (compression ignition) and the "S" series is for gasoline (spark ignition). Within each category is a series of specifications like CC, CD, CE, CF, CG, CH, SG, SH, SJ, etc. Look at the API website for better info. If you just want the short it is.

The primary difference between normal auto oil and HD oil, Syn3, Amsoil, Rotella, and many other synthetics is the "CF" standard. It is defined as "CF - Indirect-Injected Diesel Engine Service - Service typical of indirect-injection diesel engines and other diesel engines that use a broad range of fuel types, including those using fuel with high sulfur content; for example, over 0.5% wt. Effective control of piston deposits, wear and copper or brass-containing bearing corrosion is essential for these engines, which may be naturally aspirated, turbocharged or supercharged. Oils designated for this service have been in existence since 1994 and may be used when API Service Category CD is recommended. Also recommend where severe axial loads may be present."

Rotella and other diesel oil:
Diesel engines run much higher compression ratios than gas engines and they run a lot hotter, so the oil is formulated to deal with this. At first we would think this to be an ideal scenario for our performance engines...but they produce a lot more dirt in terms of combustion by-products. Diesel-rated oils typically have more detergents in them to deal with this. This is where the problem comes's not unheard of for diesel oils to clean a gas engine so well that it loses compression. Diesel-rated oils also have an anti-foaming agent in them which is unique to diesel engines, and not needed in gas engines. So what are the advantages?....the CF rating (read above).

Regular automotive oil:
Most do not have the CF rating and also lack the heavy detergents and anti foaming agents. Good but I want the additional lubrication and protection CF provides.

To make it as easy as possible...I'd want the "CF" protection that diesel oil provides but without the harsh detergents and anti-foaming agents. This rules out regular automotive oils and true diesel oils. It leaves us with HD oil and synthetics like Amsoil and a couple others...both of which have the CF ratings.