Why do oil recommendations vary for different cars?

Oil recommendations for cars depend on the engine type, viscosity, mileage and additives. It also depends on the type of driving the owner uses the vehicle for. Some engines only use synthetic oil, while others use a variety.

There are four types of motor oil, the most common of which are conventional, semi-synthetic, full synthetic and high mileage. Viscosity determines how well the oil thickens and thins in hot and cold temperatures. Viscosity types such as 5W-30 and 10W-30 are multi-grade oils tested at two temperatures. Additives such as detergents, anti-wear additives, foam inhibitors and friction additives make up to 30 percent of the concentration of motor oil.