When it comes to heavy-duty diesel engine oils, some may find it difficult to separate fact from fiction. Many myths have existed for quite some time and have become largely accepted as common knowledge. Following is a look at eight of these myths and the facts that can help dispel them.
Myth #1: Never Switch Oils
“The old belief that if you start an engine on one brand/type of oil that you should stay with that oil is really part of a long-standing myth,” says Mark Betner, manager of heavy-duty engine oil sales, CITGO Petroleum. “What gave rise to this thinking over time is that there have been infrequent reports that when changing brands of oil, there was an increase in oil consumption.”
There are many causes for increased oil consumption and switching oil brands is not one of them. “Changes in oil consumption and oil pressure are often associated with changing brands instead of actually diagnosing the root cause,” says Betner. “Oil consumption and oil pressure are more accurately impacted by a variety of factors including oil filter condition, contaminant loading, engine component condition, engine oil contamination levels and even incorrect reading of oil pressure or oil levels.
“However, when changing brands, some engine manufacturers report through oil analysis that a harmless event can occur which may result in significant increases in some of the elements reported,” he continues. “For a short period of time, some elements such as copper, potassium, lead and aluminum may appear elevated after changing oil brands or when breaking in a new engine. It is recommended to consult with your engine manufacturer and oil analysis provider to learn more about these harmless and temporary increases.”
It’s also okay to switch between conventional petroleum-based motor oil and synthetics. “Engine oils, regardless of whether they are formulated using conventional petroleum base oil or if they use some synthetic component, can be used interchangeably,” says Shawn Whitacre, senior staff engineer, Chevron.
“You can switch between these products with no ill effects. In fact, semi-synthetic oils are actually a blend between conventional petroleum-based oil and synthetic oil,” says Betner. “If the oil meets the OEM specifications, either mineral or synthetic may be used interchangeably. Any synthetic oil which has API qualification, such as CK-4 or CJ-4, can be used in any application calling for that type of oil.”
Myth #2: Beware of Synthetic Oils
The myth about synthetic oils causing leaks in current engines is false. However, it has a basis in real-world circumstances. When synthetic oils were first introduced in the ’70s, there were a few issues of seal incompatibility that resulted in leaks. These issues were corrected decades ago with a change to more compatible seal materials.
If the seals and gaskets in an engine are in good condition, the oil will not leak out. If the seals or gaskets have been compromised, that is another issue. Synthetic oils may be more prone to find the existing leaks.
Another myth surrounding synthetic oils is that they should not be used to break in a new engine. “This comes from a preconceived belief that synthetic oils are more ‘slippery’ compared to conventional oils,” says Betner. “Many years ago, engine manufacturers recommended a break-in oil, which allowed the engine parts to accelerate a wear pattern break-in condition before switching to a conventional engine oil. Synthetic oils were considered to prevent this wear break-in action from taking place, or at least prolonging that action in those older engines.
“Today, fleet managers who choose synthetic oils immediately do not have a problem or concern with how synthetic oils impact new engines,” he assures.
Myth #3: Aftermarket Engine Oil Additives Increase Performance
Another myth is that external additives may boost the performance of the oil.
Most reputable engine oils already contain optimized additives. Any additional additives could upset the existing chemistry and even decrease the effectiveness of those already in the oil.
Myth #4: You Can Determine Oil Condition at a Glance
Many believe you can tell the condition of oil by looking at the dipstick. Oil is light amber when you pour it into the engine and then quickly turns a darker color. However, this does not mean the oil is dirty. It just means it is working the way it’s supposed to — dispersing particles and holding them in suspension.
“There are a variety of reasons that oils change color as they age, and some of those things happen very soon after the oil is run in an engine,” says Whitacre. “As they say, looks can be deceiving. Chemical changes due to exposure to heat as well as the accumulation of combustion by-products, like soot, can cause an oil to become darker than when it is poured into the engine.”
Yet, there is some truth to the myth. “While you may not be able to determine the condition, you can notice items such as milky color, burnt odor and gritty material,” says Betner. “This is an old art that is greatly under appreciated. It is not a substitute for complete oil analysis, but it is good for technicians to know what to observe.
Myth #5: Oils Don’t Wear Out, They Only Get Dirty
Contrary to some beliefs, oils do wear out and need to be replaced.
“There are a number of factors that limit the useful life of an engine oil,” says Whitacre. “Clearly, the accumulation of contaminants, like soot and/or fuel, is one of them. But more commonly, it is actually the depletion of the additive system that triggers the need for an oil change. In fact, some of the additives used in engine oils are there specifically to control this breakdown, enabling the much longer oil drain intervals that are appropriate these days.”
“All oils wear out, but some faster than others,” Betner notes. “Higher temperatures can impact the longevity of the oil. Oils can become contaminated with excessive fuel, known as fuel dilution; dirt from the air induction system; coolant leaks from various sources; excessive soot; and the production of acidic or corrosive compounds that can enter the oil.” Such contaminants can render oil incapable of protecting the engine.
“Routine oil analysis is the best diagnostic tool for detecting when the levels of contamination become engine life threatening,” says Betner.
Oil can also deteriorate due to oxidation. “Oxidation is accelerated by high operating temperatures or over-extended oil change intervals,” says Betner, “which cause the oil to turn into sludge and varnish.”
“The best way to gauge the health of the oil is to conduct used oil analysis, which can provide the most detailed picture of oil degradation and accumulation of wear particles and other contaminants,” says Whitacre.
Myth #6: Oil Performance Can Be Judged by TBN or Phosphorous Content
A common misconception is that heavy-duty oils with a higher total base number (TBN) provide better engine protection.
TBN measures an oil’s neutralization number using industry standard testing. Many misinterpret a higher TBN to mean the oil can perform better. “However, the introduction of ULSD (ultra-low sulfur diesel) and engine oil chemical limits have resulted in less emphasis on higher TBN numbers and more on how the oil can maintain TBN and corrosive wear protection in severe conditions,” Betner points out.
“Today’s heavy-duty engine oils with lower TBN numbers have shown the capability of outperforming older, higher TBN engine oils,” he continues. “Equipment owners should ask for more information about how their engine oil brand performs in respect to TBN production and how it relates to another engine oil performance factor called TAN, or total acid number.”
Similarly, phosphorous levels are not necessarily the best indicator of engine wear protection. “We are hearing a lot about phosphorous content and the role it plays in determining the wear control performance of heavy-duty engine oils,” says Whitacre. “Some of this dates back more than 10 years ago, when the API CJ-4 category was first introduced. Those oils, as with the CK-4 oils that are sold today, were limited to no more than 1,200-ppm phosphorus to allow them to be compatible with catalytic emissions control devices introduced in 2007.”
Phosphorous in engine oil results from the use of zinc dithiophosphate (ZDDP). “It is a very effective wear control additive that also provides benefits by controlling oil breakdown at high temperature,” says Whitacre. “It is used in combination with other additives that contain no phosphorous to provide robust protection that is required from today’s oils. So phosphorous content simply isn’t telling the whole story with respect to engine protection.”
Myth #7: A Specific Oil Brand is Required for Warranty
Some customers are under the impression they need to use a specific brand of oil to maintain their warranty. Rather, you should check the owner’s manual and service bulletins to understand the engine manufacturer recommendations.
“Engine oil recommendations are based on engine oil API certification categories, and a viscosity recommendation for specific engines may include additional engine manufacturer approval requirements or specifications,” says Betner. “Do not rely on hearsay or opinion about how a specific brand of oil supports the engine warranty.”
Myth #8: The Heavier the Better
There is also a myth that heavier viscosity engine oils are necessary to protect large diesel engines. But in the on-highway market, there has been a transition to 10W-30 oils for improved fuel economy while still providing adequate protection.
“It is generally true that builders of large-displacement engines that are used more commonly in off-road equipment... typically recommend SAE 15W-40 oils for these applications,” Whitacre states. “There are certain situations where SAE 10W-30 oils are recommended, particularly in colder operating climates. These engines often experience higher average load factors, and have lubrication systems that were designed and calibrated to use the thicker oils.
“We always recommend that end users consult with the equipment provider to confirm the specific recommendation for the engine type, operating environment and duty cycle,” he adds.
Some erroneously believe that a low viscosity engine oil is too thin. “Licensed and approved lower viscosity oils are designed to perform well in newer engines to improve fuel economy and engine durability,” says Betner. “It’s necessary for engine oil suppliers to work with their customers and provide oil analysis along with technical support so [customers] understand what’s best for their equipment.”
Lighter viscosity oils may actually prove more desirable. “Beyond fuel economy, lowering viscosity from 15W-40 to 10W-30 can often bring additional benefits such as reduced warm-up times and less wear at startup due to better oil flow and pumpability regardless of the season,” says Shawn Ewing, product technical services, Phillips 66.