Commercial fleets are at the heart of many industries, from construction to haulage, and maintaining these vehicles is a significant investment. Everything from fuel efficiency to reliability to planned and unplanned downtime can seriously impact a company's profit margins and operational effectiveness. Strategies for keeping vehicles in good condition and on the road are imperative for good business and these include choosing the right engine oil. Since recent statistics show over 75% of American commercial vehicles have diesel engines, here we answer: Is synthetic oil better for diesel engines?

What Are Synthetic Oils?

Synthetic engine oils are chemically engineered, unlike traditional mineral oils, which are directly derived from crude oil. As a result, they can be designed to offer superior performance and protection, with chemical modifications allowing them to withstand extremes of operating conditions. They typically contain additives that confer other benefits to an engine. These include detergents to help keep components clean, anti-wear agents for added protection of moving parts, and dispersants to prevent the build-up of sludgy deposits within the engine. 

What Are the Benefits of Synthetic Oils?

There are six key benefits of synthetic oils for commercial fleets:

1. Enhanced Protection: The main function of petrol and diesel engine oils is to minimise friction between the combustion engine’s moving parts, protecting them from wear. The enhanced molecular stability of synthetic oils allows them to function at their best even while under extremes of heat and pressure. As a result, the protective barrier they create remains consistent, no matter how heavy a load is placed on the vehicle. 

The benefits of this are manifold, from reduced component degradation to fewer repairs to extended longevity of the engine. Avoiding the financial implications of vehicle downtime, breakdown, and the need for replacement of parts is of clear benefit for a business operating a commercial fleet.

2. Improved Fuel Efficiency: Synthetic oil is formulated to flow smoothly, even in extremely low temperatures, while not losing its protective capabilities when hot. Its lower viscosity when cold helps the engine pump it more easily, reducing the energy expended and minimising internal friction. This lower fuel consumption quickly translates into significant savings, especially for large fleets, those with high mileage, and vehicles with frequent stop-starts during operation.
3. Extended Maintenance Intervals: The chemical makeup of synthetic oils is modified to make them more resistant to degradation, oxidative damage, and breakdown. When compared to conventional oils, their lubricating capabilities, viscosity, and cleanliness are retained for far longer periods. As a result, the periods between oil changes and maintenance checks can be extended without risking damage to a vehicle’s engine.

Even routine maintenance schedules take a vehicle off the road for some time, while services and oil changes cost money. By extending the time between these, money is saved on maintenance costs while vehicle availability is maximised.

4. Superior Performance in Extreme Operating Conditions: Commercial fleets must often operate in challenging conditions that place engines under increased stress. Hauling heavy loads, travelling long distances, idling in traffic, dusty air, extreme temperatures, and frequent stop-starts are all taxing for a vehicle to contend with.

Synthetic engine oils are designed to perform reliably in all such environments and conditions. Detergent and dispersant additives help prevent airborne pollutants from compromising the oil’s clarity by removing impurities. The high thermal stability of synthetic oil allows it to retain its protective properties even in very high heat. Meanwhile, the absence of the paraffin and waxes that compromise the flow of mineral oils in cold climates means synthetic oil can still flow just as efficiently even in freezing conditions.

5. A Cleaner Engine: Dispersants and detergents added to synthetic oils prevent the accumulation of deposits and harmful sludge that can build up within the engine. These deposits can be corrosive to metal surfaces and inhibit the efficient operation of the vehicle, reducing performance and contributing to wear. A clean engine not only functions optimally but also helps ensure the longevity of its components, requiring less frequent repairs and replacements.
6. Lower Environmental Impact: The longer lifespan of synthetic oils and less frequent oil changes a vehicle requires when using them means less waste oil is generated. Not only that but the improved fuel efficiency that synthetic oil facilitates helps lower carbon emissions. Scaled up across an entire commercial fleet, these benefits can make a big difference in minimising a business’s environmental impact.

Which Synthetic Oil is Best for Diesel Engines?

When choosing an engine oil, it is always important to be guided by the vehicle’s original manufacturer’s recommendations. They will have thoroughly tested the engine in a range of conditions to ascertain which oil will offer the best performance and protection. Remember, too, that using oil not recommended for your vehicle will likely void its warranty.

The best oil for diesel engines will depend also on the conditions in which the vehicle will be operating. For vehicles that operate in extreme conditions, under heavy load, or that make frequent stop-starts, an oil with high thermal stability and resistance to oxidation will be best.

You will also need to check the oil is compatible with your vehicle’s emissions system and is for use in diesel engines. Checking its certification is the best way to ensure compatibility. American Petroleum Institute-certified oils labelled API CK-4 and CJ-K, or European Automobile Manufacturers’ Association ACEA E7 and E9 oils are for use in diesel engines. Modern vehicles typically require low-ash oil formulations such as API CK-4 which are compatible with DPF and SCR emission systems.

How Often Should I Change Synthetic Oil in Diesel Engines?

How often you should change synthetic oil will vary depending on the engine type, operating conditions, and oil quality. You should always be guided by the original manufacturer’s recommendations regarding oil change frequency. Checking oil clarity and levels regularly is imperative, and will allow you to change the oil before its performance is compromised.

As a rough estimate, modern light-duty diesel engines usually require an oil change every 7,5000-10,000 miles, or every 6-12 months. Heavy-duty diesel engines using high-quality synthetic fuel typically require a full oil change every 25,000-50,000 miles. Premium synthetic oils have improved longevity meaning these intervals can be extended beyond the upper limits mentioned.

Oil will need to be changed more frequently than this if the vehicle is operating under heavy load or in extreme conditions. Check your oil regularly or use oil analysis systems to monitor for signs of degradation. Changes in clarity, colour, consistency, or smell are all indications that the oil needs to be changed. Replacing oil filters with every oil change will ensure clean oil circulation, and help get the best performance from your synthetic oil.

Can You Use Fully Synthetic Oil in a Diesel Car?

Yes, a fully synthetic oil is fine to use in a diesel car, so long as the oil you choose is compatible with your vehicle’s engine. As always, follow the manufacturer’s recommendations and ensure the oil you opt for has the appropriate certification. If you are at all uncertain, it is always wise to ask a mechanic or automotive expert before using a new oil in your car’s engine.

The benefits of synthetic oils can confer significant cost-savings over time.  Their advantages range from maximising performance and enhancing the longevity of engine components, to extending maintenance intervals and guarding against unplanned vehicle downtime and breakdowns. These can each make a huge difference to a business’s profit margins when scaled up across a commercial fleet.

To discover how high-quality synthetic oils can enhance the profitability and efficiency of your commercial fleet, and get advice on choosing the right synthetic diesel engine oil for your vehicles, contact us today.  At Gulf Oil, we have over a century of experience with automotive oils and lubricants, and our experts are always happy to answer any questions you might have.