Selecting Diesel Engine Oil
for Mixed Fleets
by Kevin Mumaw, Territory Manager, Acculube
Selecting the right diesel engine oil is simple when you only have one truck. With fleets, however, there are usually different models, makes, years, and – most significantly –
different engines.
The goal is to find a single oil, or as few options as possible, that meet the needs of the entire fleet, so you can save money with bulk purchases and simplify maintenance. Fleet owners and maintenance professionals need to evaluate their equipment, the duty cycle, and the engine oil's capabilities. A reputable lubricant supplier will recommend an engine oil which meets the fleet owner's equipment needs and integrates with the preventative maintenance (PM) or service schedule.
Oil selection is determined by the type of diesel engine. The Environmental Protection Agency (EPA) raises emission and fuel economy standards every few years. When new requirements come out, the Society of Automotive Engineers (SAE) works with its members to determine how to modify engine designs to meet them. Meanwhile, oil suppliers create new formulations or change existing ones to adequately lubricate and protect new engines. The American Petroleum Institute, which represents oil suppliers, conducts standard tests to make sure oil products meet the new standards as well.
As you update your fleet, it becomes more challenging to determine which oil is best for the entire fleet.
How Different Can The New Formulations Really Be?
If you’re thinking of using your same oil for the newest additions to your fleet, think again. The differences between the new oil formulation and the old could be significant. For example, newer engines use a higher percentage of exhaust gas recirculation. The engine takes a certain part of the exhaust gas and reintroduces it back into the engine. This process creates lots of heat which can stress the oil if it's not formulated to handle it.
Stressed oil can create sludge in your engine, which can wear out parts, reduce engine life, reduce fuel economy, and increase oil consumption.
Viscosity: The Most Important Aspect of Diesel Engine Oil
Fuel economy is related to the viscosity of the engine oil. Viscosity is the thickness of the oil or, more specifically, its internal resistance to flow. The higher the viscosity, the more load the oil can bear.
SAE has a system for grading motor oils according to their viscosities. In order of ascending viscosity, SAE grades are numbered 0, 5, 10, 15, 20, 25, 30, 40, 50, and 60.
The first four of these ratings are designated with the letter ‘W’ to signify a winter, cold-start viscosity. A single-grade oil is one without a polymer additive (Viscosity Index Improver) to change its viscosity. There are eleven grades of single-grade oils: OW, 5W, lOW, 15W, 20W, 25W, 20, 30, 40, 50, and 60.
A multi-grade oil usually – but not always – employs a Viscosity Index Improver additive. The designations for multi-grade oils include two numbers: a cold-start number and a hot number for when the engine is at operating temperature. How an oil's viscosity changes with temperature is dependent on the types and amounts of oils and additives a manufacturer might use.
The Role Additives Play
Additives are critical and are often the difference between competitive oil brands. Unfortunately, most additives are proprietary. Therefore, you should look for an oil with a balance between additives and base oil. You don't want the additives to outweigh the oil. One word of warning regarding aftermarket additives - don't use them. They could void oil and engine warranties.
What Should You Do If You Have A Mixed Fleet?
If you're unsure, purchase the oil formulation for your most recent engine. It's not the most cost effective decision, but it will prevent you from damaging your fleet’s engines. Diesel oils are “backward compatible;” the newer oils work in older engines. When the new PC-11 standards are rolled out in early 2017, this is likely to become more complex.
To find the best diesel engine oil for your mixed fleet, consider working with a reputable lubricant provider such as Acculube. They understand the science behind the diesel oil formulations and are familiar with the numerous makes and models of diesel engines in
fleet service. A reputable lubricant supplier also has relationships and communications with the engine and truck component OEMs to assist with specific lubrication-related questions
or concerns.
ABOUT THE AUTHOR: Kevin Mumaw is Territory Manager for Acculube, a Dayton-Ohio based supplier of metalworking and manufacturing fluids to American manufacturers, machine shops and vehicle fleets.
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