Heavy Duty Trucking

JUL 2014

The Fleet Business Authority

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58 HDT • JULY 2014 www.truckinginfo.com different viscosity oils, tipped so they flow into a container. Lower-viscosity oils would flow faster than higher-vis- cosity oils. Obviously, you don't want one that runs like water, but neither do you want one that falls out in a big gelatinous glob. This is what is being measured in the SAE viscosity grades you're used to seeing, such as SAE 30 or SAE 40. HTHS viscosity, on the other hand, is a measurement of a type of dynamic viscosity, which measures a fluid's re- sistance to flow in the narrow confines between fast-moving parts, explains For both types of measurements, lower numbers mean lower viscosity. The new category is expected to limit the HTHS viscosity range from 2.9 to 3.2 cP for the GHG version, while the non-GHG version will be at 3.5. Current CJ-4 oils run at a minimum of 3.5 cP, Arcy says, which is in the higher-viscosity end of the acceptable viscosity range to meet SAE 30. The new low-HTHS-viscosity oils will be more on the lower end of the viscosity range found in SAE 30 oils. The new oil category In order to be ready to meet the 2017 model year requirements, the new API category originally was scheduled to be in place by January 2016, but it is now looking like it won't be ready until late 2016 or even January 2017, according to Arcy. Jeremy Dean, supervisor, chemical technology and cleanliness laborato- ries for Daimler, says some of the pos- sible concerns about lower-viscosity oils that need to be addressed in the new category, in addition to making sure overall wear rates are equivalent, include: • Scuff and seizure resistance of reciprocating and rotating com- ponents such as the cylinder kit, crankshaft, valve train, gear train, oil pump and air compressor. • Equivalent performance of engine seals (internal and external oil leaks). The category will require oils to pass some 20 engine and bench tests to make sure they can protect engines. Some tests are carryover tests from the previous category. Others carry over but with stricter limits, and two are brand-new. One of those is the Mack T-13 oxi- dation test. Oxidation is the chemi- cal reaction that takes place when something is exposed to oxygen. It is accelerated by high temperatures, and the new engines are going to run about 10 degrees hotter. In fact, Arcy says, for every 10 degrees increase in temperature, you double the oxidation. Oxidation can lead to an increase in the oil's viscosity, the Shell technical expert Seung Min Yeo. This simulates an environment more like actual engine parts operation, where the oil is being flung around at high temperatures and the molecules in the oil are stressed — deformed, stretched, and even sheared. Kinematic viscosity, which is mea- sured by unit of centistoke, is measured at 100 degrees Celsius, or 212 degrees Fahrenheit. HTHS viscosity, which is calculated by a different unit of measure, centipoise (cP), is measured at a higher temperature — 150 degrees C (302 F) — and a pre-set shear rate. Shell field-tested an experimental low-HTHS-viscosity oil against a tradi- tional 15w-40. Teardown results showed virtually no difference between the wear in these two engines. Low-viscosity oils PHOTOS: DEBORAH LOCKRIDGE

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