Diesel engines can only run smoothly with the right motor oil.
Compared to gasoline engines, diesel engines have different lubrication needs. Selecting and using the correct oil can help to slow wear, increase fuel efficiency and avoid engine damage.
In this guide to oil for diesel engines, we will discover how to identify the suitable oil for a diesel engine, helping you to make an informed choice.
Oil viscosity
When considering oil for a diesel engine, the oil viscosity must be considered.
The viscosity of an oil refers to its resistance to flow. You’ll see oil viscosity represented by two numbers – 15W-40, for example. The first number is the cold temperature viscosity of the oil, and the second number is its hot temperature viscosity.
These measurements are important, because oils thin out when naturally heated, and thicken when cooling. Looking at the viscosity of oil for diesel engines shows you how well it performs under the varying conditions of different commercial vehicles.
Diesel engines usually run at higher temperatures than gasoline engines. This means that the viscosity rating required is usually higher, in order to maintain adequate lubrication. You should buy an oil with a viscosity recommended by the manufacturer of the car or engine; this is likely to be in the range of 10W-30 to 15W-40.
OEM specifications
Specifications set out by original equipment manufacturers (OEMs) – in this case, the car manufacturers themselves – should always be taken into account.
Car manufacturers often design their own guidelines to ensure that drivers can protect their engine sufficiently, and enjoy optimum performance from their car. OEM specifications for diesel engine oil should not be deviated from.
Conventional or synthetic oil
This is another important choice, but unlike viscosity, whether you choose conventional or synthetic oil may come down to personal preference.
Conventional oils are manufactured from crude oil, while synthetic oils are comprised of compounds that have been made artificially.
People may choose a conventional oil for a diesel engine as they are cheaper, and can still offer sufficient protection. On the other hand, synthetic oils generally perform better. They can typically perform better at lower temperatures for longer, and can provide improved oxidative and thermal stability, as well as more resistance to breakdown.
With synthetic oils, you won’t need to change your oil as frequently, and you might find that your fuel economy is better than when using conventional diesel engine oil.
Special additives and formulas
From food and supplements to manufacturing materials, many products advertise special additives that make them superior to similar items on the market.
Oils for diesel engines are no different. The additives to look out for in diesel engines are usually designed to improve performance and protection.
Depending on your preferences, look out for additives that can help to enhance fuel economy, increase protection, slow corrosion and avoid sludge build-up. Additives can also help engines that operate in certain conditions – such as vehicles regularly clocking up high mileage or being driven in harsh environments. You may find certain formulas are designed to be ‘greener’ and better for the planet.
Try to pick a diesel engine oil that’s not only within manufacturer guidelines for viscosity, but that matches your use of the vehicle as much as possible.
Eco-friendly oils
Today, many vehicle owners are looking for more eco-friendly products. Environmental regulations have also increased demand for oils that are greener or biodegradable.
In general, eco-friendly oils are derived from vegetable oils or carboxylic acids and alcohols (known as synthetic esters).
When choosing eco-friendly diesel engine oils, it is also important to ensure that they match the required performance specifications of your diesel engine. And while biodegradability and reduced emissions are benefits of eco-friendly oils, you should note that these types of oils could be more costly, or harder to find with the performance specifications that you need.
Oil maintenance
Even with the correct diesel engine oil, you cannot achieve optimum performance without the right maintenance.
Diesel engines may consume more oil than gasoline engines, and so it is important that oil levels are monitored and topped up when needed.
The vehicle manufacturer should specify oil change intervals – essentially, how often you should change your oil. A high-quality oil filter is important, as this part removes contaminants from the oil that may accumulate. If oil isn’t being filtered, hard particles can develop that wear the surfaces of your engine.
Follow the guidelines and match the oil to your requirements
We’ve presented a number of factors to bear in mind when buying oil for diesel engines. However, the priority should always be to meet manufacturer guidelines in terms of oil viscosity and performance. Once you have these requirements ticked off, product features such as cost and eco-friendliness can be considered based on your preferences.
