The Differences Between Passenger, Diesel and Racing Engine Oils

The additive packages in motor oils are designed to meet the requirements of new car manufacturers and keep your engine running smoothly for years to come. It is always a best practice to use a motor oil that clearly states it meets the performance specifications as outlined in the service manual of your vehicle.

Many enthusiasts, however, seek an alternative to accommodate engine performance upgrades, high performance driving, or older vehicle specifications. Although the intentions may be good, the use of a motor oil that meets a specification other than what is recommended for your vehicle may not be wise. To help clarify, we review the three basic types of motor oils available on the market and the criteria used in formulating each below.

Passenger Car Motor Oils

Passenger Car Motor Oils (PCMO) are formulated to meet the latest engine specifications provided by the new vehicle manufacturers. The latest industry standard, GF-6, is due to be released shortly. GF-6 motor oils meet new testing requirements, including the ability to resist low speed pre-ignition.

With a greater emphasis on fuel mileage and reduced emissions, the demand for most of these oils is increasingly moving toward lower viscosities, including 5W20, 0W20 and lower. Additionally, the highly efficient, sensitive emissions systems in new vehicles have forced motor oil formulators to reduce the levels of sulphur, zinc, and phosphorus. Zinc (ZDDP) levels are currently around 800 ppm. ZDDP is an anti-wear additive that is required at higher levels in vintage automobiles. These vehicles normally require about 1,100 or more ppm to protect internal engine parts. Adding a ZDDP additive is recommended at each oil change for vintage vehicles to raise the zinc level to where it was back when these vehicles were new.

Diesel Motor Oils

Diesel motor oils vary from PCMOs in that they are formulated with an emphasis on keeping soot in suspension. As a result, they have an increased amount of cleaning agents, mostly in the form of calcium. Many diesel engine oils are formulated with higher levels of zinc and phosphorus. However, this is now changing with newer diesel engines requiring low SAPS (sulphated ash, phosphorus, and sulphur) motor oils to meet the requirements of modern day emissions systems.

Some enthusiasts believe changing to a traditional diesel motor oil is advantageous for gasoline vintage vehicles because it will have higher levels of zinc and phosphorus. Although this may be true, it is important to note the motor oil must meet the specification designated for the gasoline engine. If it does not, the change over can result in engine damage. Additionally, keep in mind motor oils designed for gasoline engines are formulated to work with the byproducts typically associated with those engines.

Racing Motor Oils

Nothing stresses an engine to its limits more than professional motorsports. These high revving applications create high heat and friction and can cause motor oils to quickly breakdown and evaporate. In formulating these motor oils, the additive packages place a greater emphasis on anti-wear and eliminating heat and friction. Less importance is placed on detergents which can extend the life of the oil since it is assumed the oil will be changed very frequently.

In summary, it is always best to consult with the vehicle's engine manufacturer or engine builder in considering the proper motor oil specification for your application. Selecting the correct specification will allow you to select the proper motor oil for your vehicle which should help extend the life of the engine.