The 9 Best Diesel Engine Oils
We spent 46 hours on research, videography, and editing, to review the top choices for this wiki. A high quality oil will protect your diesel vehicle's engine from heat, cold, wear and sludge. If your vehicle works as hard as you do, keep it running smoothly for longer with one of these, and help reduce fuel consumption, too, as a bonus. We've included both synthetic and traditional options to suit every kind of car or truck. When users buy our independently chosen editorial picks, we may earn commissions to support our work. Skip to the best diesel engine oil on Amazon.
Additives In Diesel Engine Oil
Cars are expensive and most people will do just about anything to increase their car's lifespan.
Dispersants work in conjunction with detergents to take particulate impurities away from metal surfaces.
Cars are expensive and most people will do just about anything to increase their car's lifespan. Hence, there is a large market for engine oil additives in the automotive industry. With all of the marketing hype on engine additive bottles, it is hard not to be convinced that you too should be using an additive in your oil, but is this really true?
Let's look at some of the facts. The American Petroleum Institute has specific grades for each type of engine oil. These grades are actually certifications that the oil contained within that bottle has everything needed to protect a certain type of engine. These certifications are listed on the bottle in shorthand with a format like CJ-4 or CI-4. Your vehicle's owner's manual will state what kind of engine you have, so you know what type of diesel engine oil you should be using.
All commercially available engine oils already contain a number of additives that turn standard base oil into a formula that is ideally suited for a specific engine type. Some common additives used in diesel engine oils include dispersants, friction modifiers, anti-acids, detergents, and viscosity modifiers. Each of these additives has a different function. Dispersants work in conjunction with detergents to take particulate impurities away from metal surfaces. Friction-modifiers help an oil deal with high pressure conditions, while viscosity-modifiers help an engine oil maintain the perfect viscosity across a wide range of conditions and temperatures. Anti-acids neutralize acids that are produced by engines as they run. This is just a small sample of the additives found in the average engine oil, the complete list of every additive type is significantly longer.
Since the commercially available formulas already include the best possible blend of oil and additives for your specific diesel engine type, there isn't much benefit of throwing extra additives into the mix, especially considering that the average consumer won't know what type of additive their engine oil will be lacking.
Gasoline Engine Oil Versus Diesel Engine Oil
There is a lot of confusion about the difference between gasoline engine oil and diesel engine oil. In essence, both diesel and gasoline engine oils are the same as they have a formulated blend of base oils with a variety of additives to change specific properties of the oil. The main difference between the two lies in which additives and the amount of each that are added.
Gasoline and diesel engines have different properties, which results in different contaminants in the crankcase, and the oil being exposed to different kinds of conditions. Gasoline engines wind up with a lot more moisture and tar in the oil, while diesel engines collect more carbon and become more acidic.
These oils have an additive package that can work with both engine types, but it is best to choose an engine specific oil if possible.
Typically diesel engine oils will contain higher levels of dispersants. This helps deal with the higher levels of carbon. They also have more anti-wear additives, usually in the form of zinc dialkyldithiophosphate (ZDDP), to help the catalytic converters handle the extra lead, phosphorus, and zinc they produce. Gasoline engines produce significantly less of these combustion byproducts and don't need as much ZDDP. Diesel engines also require a higher viscosity in their oil than a gasoline engine, which may produce too much heat from an overly viscous oil because their internal parts are moving at much higher speeds.
Overall, diesel engine oils will have more additive per volume than gasoline engine oils, mostly overbase detergents and dispersants, because, by their very nature, diesel engines subject their oils to harsher conditions and create a good deal more combustion byproducts.
With new, more expensive synthetic oils, it has actually become commonplace for companies to make dual rated oils, which can be used in both gasoline and diesel engines. These oils have an additive package that can work with both engine types, but it is best to choose an engine specific oil if possible. Otherwise you wind up with an oil that will work in your car, but isn't ideally suited to its specific engine conditions.
Common Diesel Engine Myths
A lot of misinformation about diesel engines is floating around out there, which has resulted in many people thinking diesel engines are less than suitable for the average home automobile, but this is simply untrue.
Another common myth is that diesel engines are dirty and belch out clouds of black smoke.
One of the most common myths is that diesel engines are slow and sluggish. You might be surprised then to learn that turbo-powered diesels actually produce more torque at the lower RPM range. This makes them incredibly responsive and able to accelerate quicker than many of their gas counterparts. It also makes them ideal for climbing steep grades. In addition to having more climbing power, they perform better at the higher altitudes. This is because gas-powered engines operate at extremely specific fuel-to-air ratios and at high altitudes, air is thinner and the air-to-fuel ratio is off. Diesel engines don't require such a specific fuel-to-air ratio.
Another common myth is that diesel engines are dirty and belch out clouds of black smoke. While this may have been true in days past, now diesel engines have to meet the same strict EPA emissions requirements as gasoline engines. They accomplish this by adding a diesel particulate filter, which traps smoke from a diesel's engine. Once the engine's computer system determines that it is time to clean the filter, this extra soot is burned off automatically by the addition of a small amount of extra fuel in the combustion chamber.
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