To start an internal combustion engine, the cranking speed must equal or exceed the minimum starting speed of that engine.
The viscosity requirement of an engine, at a given temperature, represents the highest value of the sump oil viscosity above which the cranking speed does not exceed the minimum starting speed. The viscosity requirement is determined by measuring the engine cranking speed versus oil viscosity and ambient temperature and determining the minimum starting speed.
The viscosity requirement of the most popular Italian passenger car engines has been determined. The results are presented in form of satisfaction curves giving the percentage of cars starting as a function of ambient temperature and oil viscosity.
The results show that even in the most severe Italian weather conditions a 20W-X oil satisfies about 92% of the car population; 98% is satisfied by a 15W-X, while a 10W-X ensures trouble free operations in practically all cars
COMPOSITION OF THE CUNA COLD STARTING WORKING GROUP - M. Belati - Chairman, F. Badiali, E. Damasio, R. Gozzelino, E. Migliaccio, G. Palmarini, A. Saravalle, A. Scognamiglio.