Types of Motor Oils: Which is Best for Your Diesel Engine?

Keeping your vehicle well-maintained makes all the difference in how well it performs and how smooth your drive is. Besides that, taking proper care of your vehicle ensures that your ride is safe, secure, and less likely to encounter problems. Your truck will thank you in the long run, too—a well-maintained vehicle usually has a longer lifespan and performs reliably. 

Part of regular maintenance, aside from checking the state of your truck’s parts, is changing its fluids. Something as simple as a change in motor oil immediately affects your engine’s performance—leading to a smoother drive and overall better performance on the road.

With that in mind, leaving the type of motor oil up to chance can be a recipe for disaster. As the saying goes, knowledge is power—and knowing what to look for in your motor oil is a step in the right direction.

How Engine Oil Works

Before jumping into what motor oil is best for your truck’s engine, here’s a return to the basics of how it works for your vehicle.

It’s often said that engine oil is the lifeblood of the motor. The oil is stored in a reservoir below called a sump, then spread throughout the motor through various feed pipes (or known as oil galleries). As the motor continues to operate, the oil will naturally flow downwards from the moving parts, returning to the sump. Once back in the sump, the oil is filtered to remove impurities and returned to the cycle anew.

This oil plays a major role in fulfilling two important functions: lubrication and cooling. The motor pumps the oil throughout the system, reducing friction between its moving parts and cushions them from vibrations. This means your engine gets less wear and tear, letting you keep it running normally for longer.

The circulating the oil throughout the motor system moves heat away from components like bearings, pistons, rings, valve stems, and cylinder bores. This cools down the motor, lessening the wear on its parts and avoid irregular operating conditions. High heat can also cause damage to rubber elements in the motor, like gaskets that keep fluids from leaking into other parts.

Engine oils can also have additives, like cleansing agents and friction modifiers, that help with the motor’s operation efficiency. Cleansing agents can break up larger deposits and prevent smaller particles from clumping, while friction modifiers further enhance the oil's lubrication qualities. However, the effect doesn’t last forever. As time passes, the constant exposure to heat, moisture, and air can cause oxidation in the oil. This degradation results in oil thickening, the development of sludge, formation of deposits, and corrosive wear. 

All these changes affect the oil quality, making it less and less effective at providing good lubrication and driving heat away from the motor parts. It can even affect the oil system itself, with microscopic particles wearing down on the seals that keep the oil where it should be.

This can spell bad news for your motor if left unchanged, which is why it’s recommended to have your truck serviced regularly. One of the most obvious signs that your engine oil is due for a change is the change of the oil’s color: new oil is gold and translucent, slowly turning black and opaque after being put through its paces.

Diesel Engine Oil vs. Gas Engine Oil

Deciding on what kind of engine oil to get is dependent on the engine of your vehicle. A diesel engine will require a different type of oil than a gasoline engine. It’s important to know the difference between the two oils. Otherwise, the wrong oil can be ineffective at best or cause serious damage to your motor at worst.

The main difference between diesel engine oil and gasoline engine oil is a specific additive—zinc dialkyl dithiophosphate. This additive, designed to aid in reducing wear on the motor, can seep into the combustion chamber and come out in the exhaust. The byproducts of combusting this additive can poison its catalytic converter, crippling its performance for gasoline motors. In the case of diesel motors, their catalytic converters are designed to deal with this issue. This might not be an issue if your motor was built before 1975, as it will not have a catalytic converter.

The other differences between the two types of engine oil are in the viscosity and amount of additives in them:

Diesel engine oil has a higher viscosity than gasoline engine oil. This is because it is designed to stick to the motor’s moving parts more as the gaps between them are larger than those in a gasoline motor. Putting a more viscous oil into a gasoline motor can severely affect its performance in two ways. Firstly, the oil's internal fluid friction can generate more heat, causing the oil’s lifespan to decrease significantly. Secondly, higher viscosity oil will affect its pumpability in lower temperatures, leading to additional wear from the motor’s components interacting without proper lubrication. 

Diesel engine oil also has a higher level of additives and detergents than gasoline engine oil. Given that, diesel motors generate larger amounts of soot, the oil in them needs to be more effective at cleaning and dispersing deposit formations. 

This higher additive content actually provides a bonus to diesel motors, as this means it needs replacement less often than gasoline engine oils, therefore providing a longer service life. However, putting this extra additive load on gasoline engines can be devastating to their performance. The detergents will attempt to clean the cylinder walls, causing extra wear on the seal between the rings and liner. The result? A loss of compression and overall efficiency.

Which Diesel Engine Oil to Choose 

Not all diesel engine oils are made equal. Selecting one for your vehicle can depend on several factors: price range, driving conditions, service life, and more. There are three general types of engine oils in the market, all with their own features. 

  • Conventional

This is the oldest kind of engine oil and one of the cheapest. Normally, brand new vehicles come with conventional engine oil by default. Ideally, this type of oil is best for vehicle owners with ‘ordinary’ driving styles and simple engine designs. This is due to the basic-level protection it can offer. This oil will perform poorly in freezing temperatures and is more susceptible to breaking down in sweltering conditions.  A typical oil change will last you around 3000 miles, meaning you will need more frequent changes.

  • Synthetic blend

Simply put, synthetic blend oil is essentially a mix of conventional motor oil and synthetic oil. This allows for better wear protection than conventional oils and does well in fuel economy and performance. While this type of oil isn’t quite at the level of fully synthetic oil, its price range is much more forgiving. Compared to conventional oils, synthetic blend definitely outshines the former and requires less frequent changes.

  • Fully synthetic

While conventional engine oil comes from natural sources, fully synthetic oil is 100% lab-made by licensed chemists. This means that its composition is specifically designed for maximum engine performance, allowing for the utmost fuel efficiency. You can count on fully synthetic oil to protect the motor from wear better and prevent mineral deposits. This oil can also ensure a quick startup, even in extreme temperatures, and doesn’t require a warm-up time. Due to its features, fully synthetic oils need to be changed less often, lasting 7500 to 10000 miles. The only downside is the hefty price tag compared to your conventional oils. 

Even considering your engine’s ideal use and operating environment, the market is full of options that could fulfill your requirements. In general, the three major criteria you should keep in mind when looking at engine oil are the viscosity grade, additive package, and quality certification. These criteria should help you decide on how well the oil can perform for maximum efficiency.

  • Viscosity grade

Engine oil’s viscosity grate will play a key part in how your motor performs in extreme cold and heat. Viscosity grade is determined by the Society of Automotive Engineers (SAE) and is visible on the oil’s packaging. Generally, there are two types of graded oils: monograde oils and multigrade oils. Monograde oils are split between ‘winter time’ grades with low-temperature viscosity and ‘summer time’ grades with high-temperature viscosity. 

General rules are that grades with a ‘w’ after them are winter-grade oils, and the higher the number of the grade, the more resistant the oil is to thinning.

  • Additive package

Your engine oil is a blend of viscosity modifiers and additives, which make up 20 to 30 percent of its composition. These additives, as mentioned earlier, serve to improve the performance of the oil. Diesel engine oils should have additives with the following benefits: cleaning capabilities, protection from wear, and performance boosters. 

Detergent and dispersant additives help keep your oil clean and prevent the buildup of grime, while biocides target any bacteria or microbes that feed on waste. Meanwhile, zinc dialkyl dithiophosphate, lubricity improvers, and corrosion inhibitors serve to further protect the engine from wear and tear. Other oils also contain cetane improvers which enhance fuel combustion and stability improvers that lengthen the oil’s shelf life.

  • Quality rating

The American Petroleum Institute (API) created its own grading system to measure engine oils' performance and quality level. This rating is designated by the letter ‘C’, followed by an alphabet sequence from A to J, with ‘A’ as the lowest performance and ‘J’ as the highest performance.

Check your oil’s packaging if it bears the API service ‘Donut’ symbol. This means the oil has fulfilled the API’s requirements for quality. The API’s ‘Starburst’ certification, additionally, is given to diesel oils that meet the latest standards from the International Lubricant Specification Advisory Committee (ILSAC) and are part of API’s Engine Oil Licensing and Certification System (EOLCS). This means you are buying engine oil that provides excellent protection for your motor while maximizing its fuel efficiency. 

*Note that if you have an engine with a hydraulic oil injection system (HEUI), namely the Ford Powerstroke 6.0l and 7.3l engines, you should understand that the way they operate under high pressure makes the oil has to “work” harder. So, it’s always a good idea to drain and change your oil more often in these cases.


Engine oil may seem like a small thing in the grander scheme of things, but this liquid gold can make all the difference between peak performance and possible disaster. Knowing which oil is suited for your motor can help you avoid any potential complications. Additionally, the market is full of options for conventional, synthetic, and synthetic blend oils. It’s only a matter of deciding what kind of performance and what type of environment your vehicle will be in.

At the end of the day, proper engine maintenance is a must, and picking a high-quality engine oil allows your vehicle to go the extra mile, even under tough conditions.

Give your engine only the best with performance-grade diesel engine oils, now available at Pure Diesel Power.