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What is the Best Engine Oil for a Diesel?

Featured image for "What is the Best Engine Oil for a Diesel?" blog post. Yellow bulldozer in a gravel pit.

When considering what is the best engine oil for a diesel, there are various important factors to consider when choosing the best oil.

With the various modern types of diesel engines becoming so highly advanced with their complex specialized exhaust systems, the need for diesel engine oils to properly protect them is of critical importance.

When formulating the proper diesel engine oil, the chemists must decide whether they will engineer a conventional diesel oil that meets bare minimum industry standards and also meets a low price point or choose a totally different approach by deciding to formulate a high performance synthetic motor oil that far surpasses industry standards and provide oils for diesel engines that offer maximum protection and superior performance.

A full synthetic diesel oil initially will appear to be costly and expensive, but data has shown these advanced full diesel engine oils in fact offer the most value and greatest return on their investment. A blended full synthetic diesel motor oil  is a good choice to keep an engine running smoothly under all driving conditions, while effectively protecting critical engine components

For this blog post, we’ll try to offer some comparisons between these two philosophies. By understanding the difference between a conventional diesel engine oil versus a custom blended high performance synthetic diesel oil, you’ll be better equipped to decide what is the best engine oil for a diesel.

Characteristics of the Best Diesel Engine Oil

One must determine the type of base oils being used by the manufacturer, the strength of the detergent/dispersant package, how the formulation will maintain engine cleanliness and handle potential dangerous deposits, its thermal stability, the strength of its protective oil film, the oil’s ability to reduce friction and wear, and its ability to protect against extreme pressure.

All these characteristics and factors play a part in understanding whether the oil can properly protect the difficult operating environments found in today’s diesel engines.

Diesel racing truck.
Whether you race a diesel pickup truck or you own a fleet of diesel farm tractors, it is critical to understand what constitutes an effective and high quality diesel engine oil.

Base Oils

Over the last few years, base stock oils, along with engine designs, have gone through many changes. Diesel engines require an engine oil that can operate over a vast range of operating temperatures.

The engine oil needs to offer quick startup and fast oil flow during dry cold starts so that all components are quickly covered with the sufficient protective film. When an engine is operating at high temperatures, these same base stocks must withstand elevated temperatures without thinning down or burning off.

Conventional diesel engine oils will utilize standard petroleum base stocks that have gone through the most basic of refining processes to make them adequate for blending into an engine oil. They offer average low temperature  protection and high temperature capabilities. Their thermal stability is adequate for light duty service, but if exposed to long durations of extreme operating temperatures, the oil will start to break down, leading to unwanted engine deposits such as gum, varnish, and sludge.

Also, conventional diesel engine oils, due to the minimum quality standards of the base stock, tend to consume oil if left for an extended period of time. Such an oil will unfortunately require a frequent oil filter and oil change.

Logging machine.
The foundation of any quality diesel oil starts with the base stock oils. There is a vast difference in performance between base stock oils found in conventional engine oils versus high performance custom blended diesel oils.









Because these low cost conventional diesel engine oils utilize light duty base stocks, many unwanted byproducts have not been refined out and removed during refining processes. Because of this, these byproducts tend to end up in your engine as deposits.

When looking at the type and quality of base oil stocks utilized in a high performance diesel engine oil, you will quickly see huge differences in performance.

First of all, the chemists will decide to use a blend of synthetic base stock oils that have been refined many times to remove all unwanted byproducts. These synthetic oils are of the purest and finest available. They have been severely hydrocracked and hyrdrofinished.

The specialized combination of these synthetic base stocks give the oil better cold weather oil flow and much higher capabilities in resisting extreme high operating temperatures. Whether the temperature is cold or hot, critical engine parts will retain the necessary protective film imparted by the synthetic base stock oils.

Because they are highly refined and pure, these base oils provide much lower volatility. This high thermal stability when exposed to high temperatures means the oil will not be consumed nor be evaporated away. This translates to extended service life for the heavy duty diesel engine oil , the proper volume of oil is retained so that all engine parts get the necessary lubricating oil they need, and money is saved because less engine oil is consumed. An advanced full synthetic motor oil blended with moly will save the diesel owner money on repair costs, help consume less diesel fuel, and reduce down time.

Blue semi diesel truck.
Investing in a synthetic blend diesel oil that utilizes highly refined synthetic base stock oils will keep engines clean and in service for a very long time.








Following the philosophy of engineering the best synthetic diesel engine oil that will provide the maximum performance and protection, no matter the cost of the formulation, has proven to deliver ultimately the lowest cost product. Blending in these highly refined pure base oils whereby all unnecessary byproducts have been removed allows the engine oil to stay in service far longer than a conventional diesel oil and eliminates any buildup of gum, varnish, or sludge on internal motor parts. Regardless of the type of engine your heavy duty diesel equipment has, choosing the best diesel motor oil will provide the maximum wear protection, extended performance, and the best fuel economy.

This foundation of synthetic base oils will provide the possibility of benefits such as lower repair costs, reduced operating costs, and far longer engine life.

Detergent/Dispersant Package (TBN) Strength

The majority of conventional diesel engine oils formulated for CJ-4 specs typically will have TBN values of 8 to 10. TBN is a way to determine how effective an engine oil will be at protecting and neutralizing corrosive and damaging acids being produced within a diesel engine.

The higher the TBN number, the more effective a diesel oil is at neutralizing damaging and corrosive acids. Not only is it important to know the TBN value, but even more critical is to understand whether the oil can retain its acid neutralizing fighting abilities over an extended periods of time. In other words, will it retain this TBN factor long term?

Most conventional diesel oils with these lower Total Base Numbers will offer sub-standard TBN retention. These oils need to be carefully monitored through oil analysis. If not, severe damage can be caused if acids are not quickly neutralized via the detergents and dispersants formulated into the oil.

Yellow bulldozer in a dirt field.
Diesel engines produce a lot of damaging acids and it is imperative that a diesel oil contain a robust formula of detergents/dispersants to neutralize these acids.









Again, one must consider an oil manufacturer’s market and philosophy when creating their oil. If the oil is designed to meet a low price, then the chances of the oil having a long lasting TBN retention will be slim or none. You get what you pay for, and if you’re looking for maximum protection against acids in a diesel engine, then one must entertain the idea of switching to a high performance diesel engine oil.

Such an oil will typically have a Total Base Number of 14 to 15. This type of oil will utilize a TBN booster that can deal with and control the many problems that are formed by modern EGR systems found in diesel engine designs. A TBN of 14 to 15 means that the oil has been formulated with robust volumes of detergents and dispersants.

These high quality detergents and dispersants maintain engine cleanliness during high temperatures, they offer superior protection against corrosive wear, they quickly and effectively neutralize damaging acids, and they will keep unwanted soot in suspension so that it can be filtered out.

Combine harvester in a wheat field.
The TBN or Total Base Number, of an engine oil illustrates its acid neutralizing capabilities. The higher the number the better.

Protecting Against Friction and Wear

When conventional diesel oils are formulated with minimal quality petroleum base stock oils, the notion of reducing friction becomes a non-starter. Why? These types of oils have a molecular structure that is very uneven and cause higher levels of fluid friction naturally. This is before the discussion starts on friction caused by moving parts.

Conventional motor oils try their best to deal with friction via the use of basic friction modifier additives that offer some help in minimizing friction between moving engine parts during light duty service.

If your goal is to reduce friction to the bare minimum, then a different type of oil needs to be considered. Again, your high performance custom blended diesel engine oil can help in the fight against friction.

Cement mixing truck.
The first step in fighting friction and wear lies in the choice of base oils used when making an engine oil. Synthetic base oils provide the least friction and wear for a diesel engine.









Synthetic base stock oils offer far less fluid friction than conventional base stock oils because their molecular structure is more even and consistent. Also, because these base oils are highly refined and have had all unwanted byproducts removed through all the various refining processes, these base oils flow very easily with the least amount of fluid friction.

Formulated into these highly refined base oils are advanced and proprietary friction fighting additives. One in particular that is utilized is called liquid moly. Liquid moly literally plates itself to metal surfaces, drastically reducing friction in a heavy duty diesel engine. Friction creates much resistance, which leads to an increase in temperatures. Also, friction robs engines of power and require more fuel consumption.

By adding moly to a synthetic diesel engine oil along with synthetic base oils, data has shown a reduction in friction and wear, engines have been found to run cooler, engine horsepower has been increased, and fuel consumption has been reduced.

Protecting Against Extreme Pressure

Certain engine parts can be exposed to extreme pressure. In theory, an engine oil’s job is to maintain a film or layer of oil so as to keep two metal surfaces apart so they do not come into physical metal contact with each other. A sudden shock load of extreme pressure could and will rupture this film if the load goes beyond the capabilities of the oil and additives.

Orange diesel truck.
Internal engine parts of a diesel engine are exposed to extreme pressures. To protect engine parts from these extreme pressures, use a diesel oil blended with moly.








Conventional oils are typically designed to meet a price point, not a performance point. They are ill-equipped to handle any kind of severe shock load or extreme pressure jolt that diesel engines are often exposed to.

A synthetic diesel motor oil that utilizes extreme pressure additives such as moly are designed to perform quite well even when under pressure. They are better equipped to handle heavy loads inside a diesel engine. This EP ability translates to longer engine life, drastically reduced repair costs, and much longer oil drain intervals.


Today’s engine designs expose diesel oils to much higher operating temperatures and more exhaust gasses. Together, these two issues could lead an oil to oxidize. If the engine’s EGR system is not operating at peak performance, then a conventional engine oil will quickly lose most of its protective lubricating capabilities.

Yellow diesel dump truck.
High performance custom blended diesel engine oils will offer unique chemistries that help to fight oxidation, heat, wear, and acids. Moly is an example of a unique additive that will deliver benefits such as less wear, more power, and less fuel consumption.









A diesel engine oil that has been designed from a high performance standpoint will contain a robust volume of oxidation inhibitors that work to control and counteract any potential oxidation of the oil and will eliminate any sludging problems. This translates to longer drain intervals along with a clean engine.

The unique molybdenum compound typically found in a high performance diesel engine oil will be completely soluble in the oil and will not settle nor be filtered out. The moly chemistry is quite advanced and unique, because it literally will plate itself to the metal surfaces it comes in contact with, especially during extreme heat and pressure. This protective barrier created by moly vastly reduces friction and wear.

Moly is one of the most helpful additives in fighting engine wear caused during cold dry starts. It is a fact that 80% of all engine wear occurs during cold cranking dry starts. By utilizing a custom blended diesel engine oil that contains moly, your engine now has the protection required to eliminate most, if not all, wear that is caused during dry start ups.

Also, your equipment will experience enhanced engine performance and improved fuel efficiency. When you add up all these benefits, moly in fact pays for itself.

So, What is the Best Engine Oil for a Diesel?

Hopefully, we’ve provided basic information to help you make an educated guess as to what is the best engine oil for a diesel.

Caterpillar dump truck.
The more strenuous the working environment for a diesel engine, the more critical it is to invest in the best possible diesel engine oil to protect the large investment you have made in equipment.









One specific recommendation would be to take a serious look at an oil called the Best Oil for Turbo Diesel Engines.

This oil meets the CJ-4 spec. It offers a robust Total Base Number of 15, so you can expect this oil to quickly neutralize any acids.

It offers drain intervals three times longer than the best conventional diesel engine oil. If you run this oil in your diesel engine, you can expect cooler operating temperatures, increased power, and less fuel consumption.

One added bonus in utilizing this oil is that the manufacturer offers free oil analysis! This is a nice perk because it gives you a scientific way to monitor what is happening inside your engine. This oil analysis will show you how much wear your engine is going through, it can tell you how much longer your oil can stay in service, and it can warn you of any potential problems such as your engine sucking in too much dirt or whether too much fuel is entering your engine oil.

Green John Deere tractor.
The least costly diesel oil is the one that provides the most long term benefits such as extended engine wear, lower repair costs, and less downtime.








By simply utilizing this specific oil, you are entitled to free oil analysis, which is an excellent preventive maintenance tool in helping your diesel engine perform to the best of its ability and have a long, long service life.

It’s doubtful that conventional engine oil manufacturers will offer you this free scientific oil analysis service.