Since 1911, the petroleum industry has used the SAE
Crankcase Oil Viscosity Classification System to describe and classify motor oils according to their ability to flow at various temperatures. The grades in common used today are: 5W, 10W, 15W, 20, 30, 40 and 50. The "W" indicates the oil is suitable for use during low ambient temperatures such as during the winter months. For instance, oils designated at 5W-30 provide adequate lubrications at -13°F (-25°C). Multigrade oils are able to maintain their viscosity over a wide range of temperatures. An oil designated as 10W-40 performs as well as a 10W designated oil at low temperatures, and as well as a single grade 40 designated oil at high temperatures.
The introduction of synthetic motor oils dates back to World War II and they are often described as the "oil of the future." Synthetic oils are man made, manufactured in a laboratory rather than pumped out of the ground and refined. They offer a variety of advantages over natural oils from better fuel economy, stability over a wide range of temperatures and operating conditions and longevity.
However, the use of synthetic engine oils is not recommended for the "break-in" period. Its outstanding ability to reduce wear by virtually eliminating friction between moving components is not desirable for a "break-in" oil. Certain predictable amounts of friction are required for proper "break-in" of piston and piston rings. Most builders do not recommend the use of synthetic engine oils for the first 5,000 miles of service. Thereafter it is up to the vehicle owner to weigh the cost of more expensive synthetic motor oils, manufacturer's oil classification recommendations and drain intervals.
In the past, it's been common practice to use a non-detergent/straight weight oil during the "break-in" period because it was felt that the rings would seat quicker without the film strength additives. As there has been a trend to high speed and high temperature engines, cam lobe and tappet loads also have increased, to a point where it is important to use heavy duty oils which contain an
EP (high pressure) additive right from the start. Rings will seat properly when moderate loads are applied. Applying loads to the engine for short periods of time causes increased ring pressure against cylinder walls and helps to seat the rings. This is especially important if you are breaking-in the engine with heavy duty oils. The rapid deceleration increases vacuum and gives extra lubrication to the piston and other assemblies.
Hope this helps you.
_ken
