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The growth in demand for engine coolants made from propylene glycol has created interest in engineering information on their performance. Although the properties of propylene glycol coolants and ethylene glycol coolants are similar, testing was required to determine the effects of this change for current designs at the limits of the expected range of operating conditions. The performance of propylene glycol coolants at high ambient temperatures and under high load conditions was compared to ethylene glycol coolants both on the engine dynamometer and in vehicles operated on specific sections of highway in the high desert areas of California, Nevada and Arizona and a desert proving ground. The dynamometer work was done on a high production volume 3.8 liter V-6 engine. Data gathered included temperature measurements at critical cooling system and engine metal locations at a range of coolant compositions and coolant return temperatures simulating different ambient temperatures.

A short engine sequence test, based on the Sequence VD procedure, was used to screen FFV oil candidates more rapidly. Since only one engine is needed to compare the wear-protection performance of several lubricants, engine hardware variability is not a significant issue in this test procedure. Several lubricants, some specially formulated for FFV engines, were tested using standard Sequence VD engine hardware which includes molybdenum top piston-rings. Results showed clear discrimination of the performance of oil candidates. These lubricants were also tested using an engine with chromium-faced top rings and exhibited similar performance ranking.