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Cold starting and oil pumpability were studied in a controlled field test with new and used oils. Minimum starting temperatures and the corresponding oil viscosities were established for vehicles with four, six and eight cylinder engines. Oil pumping characteristics following a cold start were also defined.
It was found that a lower oil viscosity was required as the starting temperature went down to compensate for loss of battery output. The “critical” starting viscosities were always lowest for the four cylinder engine, suggesting that new CCS viscosity specifications should be based on the needs of small engines. The benefits for using a 5W rather than a 10W lubricant were modest (2–3°C) as were the increases in minimum starting temperatures with a used oil.
The six cylinder engine was the most critical with respect to oil pumpability, probably because it had the longest oil pickup tube. A 10W/30 lubricant had better pumping characteristics in this engine than predicted by low shear visometers.
Imperial Oil Ltd., Sarnia, Ontario