Changing Oils, Changing Intervals

CI-4 oil advances lube technology in different ways for EGR and pre-EGR engines. What kind of drain interval can you expect?

With the introduction of exhaust gas recirculation engines in late 2002 came the need for a new oil standard. The new oil – CI-4 – is better suited than CH-4 to combat the additional stresses, such as higher heat and increased acids and soot, put on the engine and oil by the recirculated exhaust.

CI-4 oils must pass 15 tests instead of the 12 required of CH-4 oils, and the testing standards are more rigid. CI-4 oils have better thermal stability to deal with higher operating temperatures. Many oil formulators are now using highly refined base stocks and higher levels of oxidation inhibitor additive for CI-4.

Improved oil isn’t the only change that has been made to help ease EGR stresses. Mack increased the size of its oil pan and improved filtration. Cummins and Mack, which had long change intervals of 40,000 and 50,000 miles for pre-EGR engines, shortened their standard drain to 25,000 miles. Detroit set its interval at a conservative 22,500.

Keep in mind that these recommendations are based on conservative estimates of oil life. “As they gain more field experience with EGR engines, the manufacturers will probably be comfortable with extending drain intervals,” says Gary Parsons, a business unit manager at ChevronTexaco Global Lubricants.

Not only is there some question about what will be the optimal drains for EGR engines, but also whether the advanced features of CI-4 make it suitable for extending change intervals with pre-EGR engines.


Dan Arcy, products marketing manager for Shell Lubricants, notes that some engine manufacturers allow for extended drains on EGR engines. However, this depends upon “the type of service in which that engine is operating, very controlled conditions that take into account idle time, maintaining a certain level of fuel economy, the weight of the loaded vehicle and other highly defined factors,” Arcy says.

ChevronTexaco’s Parsons says, “In some of our field tests, we found we were able to extend drain intervals in the Cummins ISX to 45,000 miles when operating on Delo 400 Multigrade, even though the manufacturer’s recommended interval for that particular engine is currently 25,000 miles.”

Alex Bolkhovsky, product adviser with ExxonMobil Lubricants and Specialties, says ExxonMobil has supported extended intervals for a number of fleets using premium products and experiencing favorable operating conditions on a consistent basis. Mobil Delvac 1300 Super and Exxon XD3 Extra have allowed fleets to extend from 25,000 miles to 30,000 miles, and even to 50,000 miles in a few cases. Exxon XD3 Elite partly synthetic has allowed intervals to 50,000 miles and, in a few cases, to 100,000 miles. Not surprisingly, fully synthetic Mobil Delvac1 has made practical 100,000-mile changes in a few fleets, even those running exhaust-gulping engines. Note that these very long periods include filter changes with fresh makeup oil at the manufacturer’s recommended interval.

Bolkhovsky says, however, that doing this requires “identifying the service of the truck. Because of the many variables, there’s no clear number we give out.” The idle time, weights of loads carried, and fuel economy numbers must all be carefully evaluated and all must be found to be favorable. Oil analysis is used, and drains are extended only in small increments until the fleets find scientific evidence that the oil can protect the engines up to the high mileages.


Although some experts had predicted an extended change interval bonanza for owners of pre-EGR engines, oil manufacturers are more conservative. “Most operators will not want to change their drain intervals,” Arcy says. “It is reasonable, however, to use a premium CI-4 oil and to keep your drain intervals equivalent to those recommended under the old CH-4 category. In many cases, manufacturers will make certain stipulations regarding oil change intervals that do not take into account whether you’re using CH-4 or CI-4 oils.”

Detroit Diesel, for instance, allows a 3 percent maximum soot level for its engines. Manufacturers also have condemning limits on contaminants from dirt and water, and other factors, regardless of viscosity. When that’s the case, it really doesn’t matter if you are using a CH-4 or CI-4 oil. The condemning limits are the same.

In most cases, if you are not running a consistent over-the-road route, if you are involved in a lot of stop-and-go driving, if you handle excessively heavy loads or do a lot of mountainous driving, oil and engine manufacturers recommend sticking to manufacturer’s guidelines, even with the better oil.

Parsons says that even though “we have tested our engine oils in the lab at soot levels up to 9 percent and been able to maintain excellent wear control, in most applications customers will change oils before the soot levels reach 5 to 6 percent.”

“Many engine oil formulators had to improve the ability of the oil to resist oxidation, neutralize acids, and disperse soot when moving from CH-4 to CI-4 (and the related OEM specifications). Because they have been improved in these areas, these oils should perform even better in non-EGR engines,” Parsons says.

Bolkhovsky of ExxonMobil says the critical point is the limiting factor that has forced you to change in the past. “If contamination is the limiting factor, you won’t be able to extend,” he says. “If your factor previously was wear, and deterioration of the wear additives was limiting your interval, you also would not be able to extend, as wear additives were not one of the step-out factors.”


Because Mack’s off-road engines and Caterpillar’s ACERT engines don’t use water-cooled EGR, the two companies are having to enhance certain specifications even with CI-4. In Mack’s case, it’s a matter of combating higher levels of soot and heat. In the case of Caterpillar’s Acert, soot and heat are less of a challenge, but piston deposits are of some concern.

Mack’s ASET off-road engines avoid the complexity of a variable geometry turbo and an exhaust gas cooler and its plumbing. They simply recirculate the exhaust with a different camshaft that gives more valve overlap between the intake and exhaust strokes. This engine also uses a cylinder head with less swirl action for the combustion chamber. (Swirl helps minimize soot, but it can boost NOx.)

“We’re still gathering data on the ASET engines,” ExxonMobil’s Bolkhovsky says. “Since there’s less cooling, heat is more of an issue. It’s still within the realm of other EGR engines, but you should also pay special attention to viscosity changes as a result of soot.”

“One thing we have noticed so far is that the internal EGR engines are generating higher levels of soot than cooled EGR,” Shell’s Arcy says. “That’s why Mack is going to soon issue a new specification. Again, Shell recommends following the manufacturer’s guidelines. In most cases, off-road applications are not good candidates for extended service intervals, anyway.”

“Actual field experience has shown that these ASET vocational engines produce a unique type of soot,” ChevronTexaco’s Parsons says. “Mack is in the process of introducing an updated specification that will include a test to assure proper soot handling performance in these engines.” The new specification will be introduced this year.

How about Caterpillar’s ACERT engine? It uses twin turbos and camshaft changes to chill the intake charge, adds a very small amount of internal EGR and spreads out the combustion by starting and stopping injection more than once. Parsons says Caterpillar wants to limit total base number (TBN) and ash levels, both of which have tended to rise with CI-4.

“The Cat bridge and ACERT engines have some unique lubrication requirements. Cat is saying that piston cleanliness is extremely important. They are concerned with pistons getting too dirty, which causes the rings to stick and oil consumption to rise,” he says. “Since the ACERT engines don’t use EGR, they don’t necessarily require the higher levels of TBN to neutralize the acids brought in by the EGR gases.”

“There is less heat concern, and soot and acids are not as large a concern since they are linked to EGR,” Bolkhovsky says.

All this leads to the new Caterpillar ECF-1 specification. “Cat-approved oils must run and pass an additional engine test, and meet CI-4 or CH-4 performance levels,” Arcy says. “Cat is basically looking for a motor oil that has the proper balance of detergents and dispersants. Caterpillar Acert engines can still benefit from many of the formulation changes made in moving from CH-4 to CI-4 oils. The improved thermal stability and soot handling of the new formulations can benefit Caterpillar engines in extended drain intervals.”

With acids and soot high on the list of oil contaminants, wearing goggles is a smart idea when changing oil. A dark color indicates the detergents have soot and other impurities in suspension so they will be carried out of the engine when the oil is drained.


What should you look for in an oil analysis from an EGR engine? Viscosity is especially critical. Oil thickens in two ways: oxidation from heat (depending upon how stable the oil is) or a high content of soot that is not adequately dispersed. Sometimes both factors are at work. Because heat and soot levels are likely to be higher with EGR, you have to monitor viscosity carefully.

Alex Bolkhovsky, of ExxonMobil, says that either an engine cooling problem or a low-performing oil can accelerate viscosity increases. “But if viscosity is stable, you’re OK,” he says.

The other increased threat from EGR is acid. This means you need to watch TBN (total base number) and TAN (total acid number). “TBN is not a defining factor, it’s merely predictive. TAN is a defining factor. If TBN is higher than TAN, that’s good,” Bolkhovsky says. “The oil should be changed when the TBN and TAN lines cross, or when the TBN drops to 2,” Parsons says.

It’s also important to monitor wear metals. “Acids will attack the metal with corrosion. It actually leaches metal from the surface,” Bolkhovsky says. To optimize the change interval, you need to carefully find the point where the amount of metal per mile deposited into the oil starts to noticeably rise, then back off. “The minute it starts to take off, you know you’ve gone too far,” says Bolkhovsky. This signifies the metal has started to flake off because of the acidity rather than normal wear.

As always, monitor water and glycol levels, fuel levels and contaminants from outside to make sure you don’t have a failure in a fuel system, cooling system or air cleaner seal that could hurt the engine.

Large oil manufacturers and engine manufacturers and dealers can provide oil analysis reports. They usually cost $13 to $20 and require about a week for results. The analysis tells you a lot, but to get the most out of the reports, get them on a regular schedule – at every oil change under established safe intervals – and look for unusual trends.


Cummins and Mack have shortened their standard drain intervals for EGR engines to 25,000 miles. That would occur well within the safe period for these sample engines, based on their oil analysis summaries, which show enough base content (TBN) to neutralize the acidic content (TAN). An oil change would be critical by 47,000 miles, when acid would begin attacking engine metals.

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