Sam Yardumian of Pennsylvania asked about the proper oil for a 2005 Jeep Liberty CRD equipped with a VM Motori four-cylinder diesel engine. It had 98,000 miles when he bought it and is now at 182,000 miles. Chrysler recommended Mobil 1 SAE 0W-40. Sam had some work done on the engine, and the oil was changed to Pennzoil synthetic SAE 5W-40. Recently, an engine technician recommended API CF engine oil, which we all know is obsolete.

Sam wanted to know the proper oil category and viscosity for his engine. I responded that he should check the owners manual first, but that the manual was probably not going to note the current oil category. The API system includes the provision that any oil meeting one of its service categories-the most recent being API CK-4 for heavy-duty diesel engine oils-must be backwards compatible so that any earlier category will be satisfied by the current oil.

As far as the viscosity grade is concerned, local conditions would drive the choice. I dont think that the fact that Mobil 1 SAE 0W-40 or Pennzoil SAE 5W-40 are synthetic is the issue; rather, it is the viscosity grade that determines oil use in this case.

Backwards compatibility was a continuing discussion item in 2018. Lake Speed of North Carolina wrote in support of my March column on the subject (Engine Tests Come Under Scrutiny), saying that he fully endorsed the idea of abandoning the backwards compatibility concept. Lake noted that the limitations imposed on the development of formulas specific to modern engines, such as those with turbocharged direct injection, places an undue and unproductive burden on products intended to provide value for the end user.

He felt that it would be more valuable for consumers if different oils were tailored to meet the needs of either older engines or modern engines. That would free up formulators and oil marketers to make the best use of the technologies available to them to manufacture high-value products for each market-older vehicles and modern vehicles. He also identified the latest API categories for diesel engines, which are split into a backward-
compatible category (CK-4) and one strictly for use in newer engines (FA-4), to make the suggestion that its time to do the same on the gasoline side.

Ive thought for a long time that, by making oil categories backwards compatible, the industry may be compromising performance for older engines as well as adding complexity to the oils for modern engines. I also responded that it causes additional testing to be run and keeps some of the older chemistries in place when they could be replaced with something better.

The industry is slowly heading toward engine builders specific oil recommendations, which will be an even bigger nightmare for those whose business is changing oil. General Motors does it now with Dexos, and Ford is headed that way as well. Of course, foreign original equipment manufacturers have their own specifications for oils. Do-it-
yourselfers will have to go on a search for the right oil for their engine (not just vehicle brand). For a fast oil change shop, it would be impossible to keep all the oils that would be needed.

Time will tell what the industry finally decides, but I think that there will be some big changes in the next few years.

Engine Testing

Russell Sas of Montana suggested that an engine test could be easily developed to measure wear protection. His idea is interesting, but the need for precision would make test development a lot more complex.

I offered a background on engine testing (see my March 2018 column), pointing out that engine tests are developed based on the need for information and to determine what level of performance is needed. For the oil industry, as well as the additive industry and engine builders, tests need to comply with current hardware, reference oils are needed to calibrate the test to reproduce a result, and so on.

Im a pretty big advocate for engine testing, since there is so much going on in an engine that really cant be reproduced in the lab. The downside of engine testing is the cost. For API CK-4, the unofficial tally was a cost close to $400 million to bring the program to a successful finish. There were two new tests and revisions to one.The cost for any new engine test would be astronomical.

Test engines use standardized parts, especially pistons, bearings, cams, lifters and others. The blocks last for a while, but typically not for more than 10 to 12 tests before they are replaced. Most of the interior parts are made by an outside shop and are not factory produced. In fact, any part that is being rated for deposits, wear or corrosion is specially made to improve repeatability and reproducibility.

Operating Temperatures

I got a letter via snail mail from Grant Sheldon in Kentucky asking about operating temperatures. He wondered if higher temperatures (220 degrees Fahrenheit versus 200 F) would be beneficial in his 2008 Cummins ISX heavy-duty diesel engine, specifically if an SAE 15W-40 would clean better. The drain interval for his truck is 13,500 miles.

In general, running engine oils at 220 F vs. 200 F is not a good idea. There is a rule of thumb used by oil formulators everywhere that for every 18 F (10 C) increase in oil temperature, the oxidation life of the oil is cut in half. Of course, there have been some significant changes in oil chemistry since 2008 that have greatly improved oxidation resistance. In addition, I commented that his drain intervals were pretty conservative at 13,500 miles, so he would still be well protected. As oil temperatures go up, viscosity drops, and with it there is probably a small improvement in fuel economy. In general, he should be okay with the temperature recommendations from Cummins.

Aftermarket Additives

Alex Dzidek up in London, Ontario, owns and operates a small lube shop in Toronto. His questions were about aftermarket oil additives, which are commonly known as oil stabilizers. He noted that there seems to be a lot of conflicting information about what these products actually do. Some users claim that they improve all sorts of issues and swear by them. Equal numbers dont touch the stuff, claiming all these products do is dramatically increase the viscosity of the engine oil.

Alex asked who is correct and what these products actually do. Stabilize is a very broad term that, without context, doesnt really mean anything; and if it really just thickens oil, can it be harmful in some circumstances? Whats the impact of pouring in a liter of one of these stabilizers along with three liters of oil into a four-cylinder engine vs. pouring a liter of product with 10 liters of oil into a big block truck?

Aftermarket oil additives have been around for a long time. I talked about some of the different types of additives in my April 2018 column, Additives, Again. Typically they are viscosity index improvers, which are very heavy, high-viscosity polymers. Some of the more sophisticated products also contain other additive components such as antiwear agents, friction modifiers, oxidation inhibitors and detergents. The name oil stabilizer is designed to make you think that oils are unstable and need extra help to maintain their quality. Its a nice catchphrase, but its not very accurate.

Raising oil viscosity probably raises oil pressure, reduces smoke (unless the rings are totally shot), reduces oil consumption and protects worn engines. It doesnt improve fuel economy, since the best means of improving fuel efficiency is by lowering viscosity. Adding an oil supplement could cause the final mixture to no longer meet API category requirements. Basically, that means the addition of an oil stabilizer in the recommended dosages will alter the performance of the initial oil, possibly causing it to fail one or more of the qualification tests.

I also noted that newer engines are now calling for lower viscosity oils, and they are designed to run on SAE 0W-20. In Arizona, where I live, summer temperatures can reach 113 F and winter temperatures can drop to 40 or 30 F. I use SAE 5W-30 year-round in the 3.5-liter V6 engine of my 2008 Nissan Quest. It now has about 141,000 miles on it and continues to perform very well.

Universal Oils

Blaine Ballentine of Iowa asked how a universal oil can meet both API SN and API CK-4 limits if the Resource Conserving designation covers SAE 0W-20, SAE 0W-30, SAE 5W-20, SAE 5W-30 and SAE 10W-30 viscosity grades and has an upper phosphorus limit of 0.08 percent by weight.

In my response, I noted that the latest footnote on universal oils in API 1509 (Engine Oil Licensing and Certification System) states that for API CK-4/SN or FA-4/SN, all properties and tests related to the API SN passenger car engine oil service category must be met. For API SN (or I suppose, SN Plus), the maximum phosphorus limit of 0.08 percent by weight must be met, but only for the previously mentioned SAE viscosity grades. All other viscosity grades have no limit on maximum phosphorus content.

Since SAE 15W-40 is the main viscosity grade for the heavy-duty market, there would be no problem. SAE 10W-30 API CK-4 oil is becoming much more popular, since it offers some fuel economy benefits for heavy-duty engines and is typically what engine manufacturers use for factory fill. In that case, the universal oil label would not fit.

As I said at the beginning of this column, you readers are very astute and ask some very important questions. My hat is off to you! Please keep those emails and letters coming. Ill try to give you the information you need.

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.