Factors Affecting Pumpability and Cold Cranking in Heavy Duty Diesel Truck Engines at Low Ambient Temperatures - Part II 920023

The cold starting and low temperature pumpability performance of twenty-one new and used multigrade oil formulations was determined in fired engine tests conducted with Caterpillar 3406B, Cummins NTC-365 and Detroit Diesel S-60 heavy duty engines. Viscosity grades included SAE 0W-30, 5W-40, 10W-30, 10W-40 and 15W-40, formulated with various commercial viscosity index improvers (VII's) including olefin copolymer (OCP), dispersant multifunctional olefin copolymer (MFOCP), polymethacrylate (PMA) and styrene-isoprene copolymer (SICP).

Significant differences in pumpability characteristics were observed among the test engines, but there was no evidence of pumpability problems with the oils evaluated. In fact, significant pressurization of the oil delivery system occurred during engine cranking, prior to ignition. Good correlations were observed between the MRV test oil viscosities and pumpability characteristics in the test engines, both on an individual and on an average engine basis. There was no evidence of any bias in these correlations for the VII type used in the oil. Increasing the engine speed from 1000 rpm to 1800 rpm was found to have little effect on the initial oil pressurization curves. Aging of the test oils in over-the-road fleet service resulted in significant changes to their low temperature viscometric and oil pressurization characteristics, but did not affect the pumpability correlations developed for all of the oils in the program.

Engine cranking speed, as determined prior to ignition, was found to correlate with the logarithm of the oil's cold cranking viscosity at the test temperature, although the correlation equation was unique for each engine. From the data, the minimum cranking speeds required for ignition could be estimated for each engine; in all cases, the engine cranking speed was well above this minimum at the J-300 limiting viscosity of 3,500 cP.