Truck News


Motor oils (August 01, 2002)

With the September deadline for the new engine oil category C1-4 now upon us, you've likely been hearing much about the new motor oil formulations. But in weeding through all the rhetoric, you should ...

With the September deadline for the new engine oil category C1-4 now upon us, you’ve likely been hearing much about the new motor oil formulations. But in weeding through all the rhetoric, you should keep one thing in mind: not all oils are created equal.

Let’s start with some misunderstandings that have cropped up regarding standards. First, the API standard that takes effect September 5 is not the only, and certainly not the toughest, new standard coming into force. The CI-4 standard does replace the old API CH-4 standard introduced in 1998 and is needed to deal with the punishing requirements of the new cooled EGR engines, which reduce N0x emissions but also run at significantly higher temperatures and create more soot. But both Cummins and Mack have come to market with even tougher standards. The Cummins standard, CES20078, incorporates all the CI-4 limits plus one extra test, a Mitsubishi valve wear test for slider followers. Mack’s EON-Premium Plus specification, meanwhile, takes the CI-4 limits and lowers them significantly. While it’s likely all major oil manufacturers will be able to meet the CI-4 standard and most will be able to meet the Cummins standard, only a selective number of oils will also be able to meet the new Mack spec. So read the label; an API donut doesn’t mean the oil also meets the other standards.

Drain intervals are a major concern with the new engines and motor oils. It would be advisable to take any claims you hear at this point with a grain of salt. The emissions standards deadline that provided the impetus for moving to the new engines was moved up by two years. Engine manufacturers have had to move faster than usual to get their new engine designs ready. As a result, both engine and motor oil manufacturers don’t have the amount of data they normally like to see before they release a new product. It is likely, however, that oil drains will have to be reduced to maintain engine durability. By how much has yet to be defined.

One of the main tasks motor oil must perform is to prevent the metal-to-metal contact that leads to wear, scoring or seizure of engine parts. To do so oil must circulate quickly upon engine startup to lubricate all moving surfaces. This full-film lubrication occurs when the moving surfaces of the engine are kept constantly separated by a film of oil. Crankshaft bearings, connecting rods, camshaft and piston rings usually require such full-film lubrication. What determines the ability of oil to constantly keep engine parts separated is its viscosity at its operating temperature. When the viscosity is high enough to prevent metal-to-metal contact, engine wear is negligible. When a continuous oil film between moving parts can’t be maintained there will be intermittent metal-to-metal contact between the high spots on the sliding surfaces, a condition referred to as boundary lubrication.

Wear control is particularly important with EGR engines. The new engine design places exhaust gas, which has been cooled from about 1200F to 300F, back in with the inlet air into the cylinder. Diesel fuel contains sulfur, which under combustion forms acids. The motor oil will have to be able to neutralize that acid to protect the rings, liners and bearings. The proper balance of the total additive system is essential to satisfy all lubrication conditions and motor oil manufacturers have had to boost their additive packages to meet the challenge.

Although the viscosity of motor oil must be high enough to maintain an unbroken film on engine parts that require such protection, it should also not be so high that it requires the engine to work harder than it needs to. Soot, dirt, oxidation or sludge increases viscosity. Soot that escapes past the rings and into the crankcase can also combine with water to form sludge and varnish deposits on critical engine parts. Sludge buildup can clog oil passages, which reduces the flow of oil. Varnish buildup also restricts oil circulation, interferes with proper clearances and can make vital engine parts stick and malfunction.

Preventing soot formation has become a key challenge for motor oils with the new engines. To lower NOx emissions engine manufacturers have retarded fuel-injection timing, which reduces combustion efficiency and can increase soot production. To deal with the new load of soot, motor oils must be formulated to disperse large amounts of soot without thickening. Good soot dispersal will stop large particles agglomerating, prevent abrasive wear developing and inhibit the formation of sludge.

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