Going back to the 1970s, drain intervals were pretty short. At that time, recommended oil changes in the range of 6,000 to 12,000 miles were the norm. There was one exception: Detroit Diesels two-cycle engines. Their drain interval was based on duty cycle and was virtually non-existent, since they consumed oil at the rate of about a quart every 200 miles! At the time, the viscosity recommendation for engines was SAE 30.

In the early 1980s, a new viscosity recommendation was introduced, SAE 15W-40. I remember the struggle to gain customer acceptance for the new grade. I was at Pennzoil at the time, and we had both an SAE 15W-40 that was probably API CD/SF, and a superior formulation, which was also API CD/SF but had higher ash content and total base number. We had put together a pretty good advertising campaign touting both and the fact that they were SAE 15W-40.

Among other things, we were claiming that both products had less oil consumption and improved protection. The president of Pennzoil challenged us on both claims, and we had a meeting with him to present our case. The biggest issue for him was oil consumption. How could an oil that was made from lighter-viscosity base oils (100 neutral to 250N) have lower oil consumption than an SAE 30 (600N to 150 bright stock)?

The simple answer was that the oil film on the liner walls was thinner with SAE 15W-40, and less was swept into the combustion chamber by the piston rings. In addition, the improved performance of the additive package resisted oxidation better. We won our argument, but it seems to me that we downplayed the oil consumption aspect a bit to make our boss feel more comfortable with it.

In his article, Marsh told the story of an oil marketer from Citgo who made a presentation to a large fleet on the virtues of SAE 15W-40. The marketer said, I remember sitting in front of a very large fleet in the early 80s trying to explain why SAE 15W-40 engine oil would be an improvement over SAE 30. I explained that it would reduce engine wear; it would reduce upper engine deposits. It would even reduce oil consumption.

He went on to say that the fleet decision-maker in front of him was very courteous and listened through the whole spiel. At the end, he said, That was a good presentation, but I want you to take something back to your engineering friends for me. … Tell them that an SAE 15W-40 oil will never work in a diesel engine.

Well, as we all know, SAE 15W-40 did work, so well that even today the marketplace is over 80 percent SAE 15W-40. Now there is a new change coming.

Two years ago, the American Petroleum Institute approved the new, fuel economy version of API CK-4 and called it API FA-4. The industry reacted by not moving quickly to support this fuel-saving, emissions-reducing lubricant. Thats not surprising given the skeptical nature of fleets toward change. They need to keep their fleets running and not in a repair shop, so caution prevails.

Part of this reluctance is due to the very fact that when SAE 15W-40 was introduced and finally accepted, it became the most successful viscosity grade across the board and has been for over 30 years. It has a tremendous track record of lubrication in diesel engines. However, the newest engine designs have moved past the venerable viscosity grade.

Some of the problematic issues with SAE 15W-40 include low-temperature pumpability. In the northern tier of U.S. states and into Canada, very-low temperatures (below about minus 10 degrees Fahrenheit) make it hard to pump oil. SAE 10W-30 buys you about ten more degrees, down to about minus 20 F. It also gives an approximate 1 percent improvement in fuel economy.

Both API CK-4 and FA-4 have an SAE 10W-30 viscosity grade, but with its lower high-temperature high-shear rate viscosity, FA-4 buys another 1 percent or so in fuel economy. The new CK-4 and FA-4 categories offer improvements in oxidation resistance, shear stability and air entrainment properties.

API FA-4 has limited use at this point. API reports that there are over 1,100 CK-4 licenses registered, while API FA-4 licenses are at about 100 and counting. The pace of FA-4 use is being slowed by its HTHS viscosity limits of 2.9 to 3.2 centipoise, which are lower than the 3.5 cP minimum for CK-4 and prior categories. For FA-4, this results in a lack of backward compatibility and makes it risky to use FA-4 in older engines.

Engine builders are using manufacturing processes that are precise and create tight tolerances, and the latest engines employ technologies to maximize power and reduce emissions as much as possible. As a result, they tend to run hot and at higher pressure.

So what does that mean for the oil? The first thing is that lowering the HTHS viscosity will result in lower friction in the engine and better fuel economy. Second, the higher temperatures and loads mean that these oils must have better oxidation resistance and wear protection. Better soot control is also a must.

Formulating for all of these characteristics calls for some pretty robust components in the finished oil. Base oils, the major component in any oil, must be more stable than in older formulations. In addition, they must be lower in viscosity than previously used while retaining very low volatility properties. At this juncture, API Group II and Group III base oils are the preferred materials. Because of their refining, they have enhanced stability and are generally lower in viscosity and volatility.

The high-temperature engine operations require additional antioxidants to combat deterioration of the engine oil. This is well-known technology, but with a different spin because of the improved base oil quality. Along with that, better wear protection is required. The antiwear agents used are also antioxidants, so theres extra bang for the buck. Soot control requires the latest dispersants be designed for higher temperature operation. The whole package is uniquely designed to work with the latest heavy-duty engines.

Viscosity is key to the whole package, and that is what brings fuel economy benefits. Marsh noted in his article that, CJ-4 and CK-4 oils have the same HTHS range. Theyre designed to flow and hold up at the same rate under higher engine temperatures and speeds of moving parts. FA-4 oils take things up a notch with a lower HTHS range … and have lower viscosity to reduce engine friction and increase fuel economy.

All of the improvements in oil and reduced viscosity have allowed original equipment manufacturers like Daimler Trucks North America to extend drain intervals in its DD13, DD15 and DD16 engines. For example, in a DD15 long-haul on-road truck, CK-4 and especially FA-4 have enabled drain intervals of 75,000 miles, compared to 50,000 miles using CJ-4. Obviously, thats a big shift (1.5 times longer) in drain intervals. It increases on-road time and reduces fuel use when an FA-4 oil is used.

So, once again, we get to the point that we need to read the owners manual, so to speak. The OEMs build the engines and know whats best for them. However, fleet managers should also be talking with their oil supplier about the best choice of oil for their trucks. They could use products based on conventional base stocks, but there are semi-synthetic and full-synthetic versions available. There are oil economics to consider as well as the duty cycle, including climate and terrain, to include in the analysis.

The bottom line for all of this is to follow the OEMs recommendations and work with the oil supplier to make the best choice. We all need to work on moving to the best possible oils and work with the OEMs to develop the additional confidence needed to capture the benefits of FA-4.

Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at steveswedberg@cox.net.