For heavy-duty diesel engines, CK-4 and FA-4 lube oils are replacing CJ-4 formulations. Here’s what you need to know.

Of all the big changes coming at you in 2017, one of the quietest, but most beneficial may be the switch over to a new type of heavy duty diesel engine oil.

For the last 10 years, all of you have been using a type of lube oil that is classified as CJ-4 by the American Petroleum Institute. If you look closely at the jugs or barrels of oil you’ve bought in the past they have a circular API logo on them (often called the “donut”) with the viscosity rating in the center of the circle and the CJ-4 designation printed on the perimeter of the circle. (See illustrations.)

Out with the old

The old CJ-4 oil category was developed by the lubrication industry to better protect engines that had Tier 3, Tier 4 Interim and Tier 4 Final exhaust emissions reduction technology. These engines generated considerable amounts of soot in the combustion chamber and ran hotter than previous diesels.

But after 10 years, the engine manufacturers began asking for additional improvements in two areas of lube oil performance. First: They wanted more engine protection for their low-emissions engines and extended oil drain intervals. Second: For newer on-highway engines manufacturers wanted the same protections but lower viscosity formulas that could increase fuel economy.

The oil industry responded by developing two different oil standards, its first “split category.” Until this year contractors put the same oil in their dozers and backhoes as the guy running 18-wheelers put in his trucks. The only difference might have been in viscosity. But as of late 2016, the industry started formulating two types of heavy-duty diesel engine lube oils: CK-4 and FA-4. Here is the difference:

CK-4 is for use in all off-road diesel equipment and older models of heavy-duty trucks. It is backwards compatible with all your older equipment and trucks. Anything you’ve put CJ-4 oil in will do fine with CK-4 oil. The only difference is the CK-4 oil will protect your engine better and may enable you extend drain intervals past what you had been doing with CJ-4.

FA-4 is formulated to give you the same robust performance and increased protection but in lower viscosity formulas that can help improve fuel economy. The FA-4 oils will not be available in a 40-weight viscosity which limits their backward compatibility for many older trucks. As of right now, no off-road engine manufacturer or vocational truck manufacturer has approved FA-4 oils for use in their engines, but oil industry experts say that may change in the future as OEMs do more testing. The truck fleets that use on-highway engines, however, need this low-viscosity formula not just to save money on fuel, but to meet increasing stringent “greenhouse gas” targets.

Practical matters

The old CJ-4 oils will soon start to disappear from the oil companies’ inventories, and eventually be completely replaced by CK-4 and FA-4, which started hitting the market in December 2016. So, you will see the new formulations coming your way soon, if you haven’t already.

Since these new oils offer performance enhancements you might want to take this opportunity to conduct some extended oil drain interval tests with the new oils to see if you can get more miles or hours out of the new formulas. And if you’re already doing regular oil sampling make sure your lab knows about the change.