http://nulon.com.au/facts/Factsheet%20103.pdf "Facts and Fallacies Australians traditionally are of the opinion that our conditions are tougher than anywhere else in the world, hence we must have thick, gutsy oils to provide protection. By and large, this is absolute rubbish. In most parts of Australia conditions are quite temperate. Conditions in Australia are no tougher than in the Arizona desert or, to the other extreme, Alaska. We are fortunate in that we can use the same viscosity oil all year round. In Europe and North America a car has to be prepared for the winter months, and again for the summer months. Part of the preparation includes a change in the viscosity range of the engine oil to cope with the extreme temperature conditions. Some unethical manufacturers are producing and marketing oils of such high viscosity they are not recognised as meeting industry standards. The general public and resellers are being led to believe high viscosity oils offer a greater level of protection and reduced oil consumption"