A Cold Start and Pumpability Study of Fresh and Highly Sooted Engine Oils in 1999 Heavy Duty Diesel Emission Engines

The new API CI-4 category defines oil quality suitable for 2002 EGR-equipped heavy duty diesel engines. Included in the category is the first used oil low temperature MRV (Mini-Rotary Viscosity) limit. Over the past 15 years heavy duty pumpability studies have been the focus of a number of studies but few have evaluated used engine oils, particularly at the high soot loadings expected in EGR-equipped engines. To gain a better understanding of rheological effect, Imperial Oil initiated fired pumpability tests of sooted and fresh oils. Three 1999 model year Class 8 heavy duty diesel trucks equipped with engines from three popular manufacturers were chosen for the study conducted in Imperial Oil's All-Weather Chassis Dynamometer. Fresh 15W-40's were compared to used 15W-40 oils taken from severe line-haul service where soot loadings were in the 6-7% range; limited testing was also conducted on a fresh 0W-40 formulation. Included in the study was a fresh 15W-40 formulated to have relatively high MRV viscosity at typical starting temperatures. Warm booster batteries and low cloud point diesel fuel were employed to enhance the probability of starting in conjunction with the original cold start systems installed on the engines. The intake manifold heating system on one of the engines was not effective as a starting aid and was replaced with an on-board ether injection system similar to the other two engines. Cold starts could be achieved in the range of -17°C to -25°C depending on engine type, viscosity grade and soot load; corresponding to cold cranking simulator viscosities in the 7000-9000 mPa-s range at these temperature extremes. Significant oil pressure was observed during engine cranking prior to ignition in most cases and none of the engines exhibited air-binding tendencies. However, notable differences were observed in oil pressurization times among the three engines. In general, pressurization times were found to increase with increasing MRV viscosities, with no apparent differences between fresh and used oil correlations. As expected, the 0W-40 formulation provided excellent cold starting performance and rapid oil pressurization in all three engines at the lowest test temperature.