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Heavy-Duty Diesel Engine Oils vs. Passenger Car Engine Oils: what is the difference?

It is indicated by their names that heavy-duty oils, which are oils used for commercial transport, agriculture or mining equipment (also known as HDDEO’s) and passenger car oils are used for different purposes. However, what is the actual difference in the composition of the oils, and why are the requirements for oils in heavy-duty machinery different from passenger cars?

The difference between the two oils lies in four areas:

  1. the composition of the oil
  2. the use of the oil
  3. the specifications and requirements of the engines
  4. the overall conditions under which the oil needs to perform.

In heavy-duty machinery, the engines RPM and power per volume (the amount of power an engine can produce in relation to its cylindric volume) is considerably lower than that of passenger cars. On top of that, the engines need to handle a larger load than the engines in passenger cars—this means that the engines in heavy-duty machines are considerably larger to handle the load. Due to the engine being considerably larger, a higher volume of oil is needed to lubricate it and helps the engine function properly.

Along with this, heavy-duty engines usually produce more soot. Soot is a product that is almost always formed during the combustion process when a carbon-based fuel (gas, petrol, diesel oil or wood) is burned. Soot mainly consists of unburned carbon molecules and is the formation of soot is heavier when not sufficient air (oxygen) is present. To combat this build-up of soot, the oil used for heavy-duty machines must have additives such as detergents and dispersants. These additives prevent the agglomeration of soot into undesired sludges or abrasive particles and are required in higher volumes than in passenger car oils. The viscosity of the oil in heavy-duty equipment also differs from passenger car oils, because heady duty engines operate at a higher load than passenger car engines. Motor oils become thinner as they heat up, and thicker as they cool down, which is why using an oil with the wrong viscosity can lead to overheating, break down in the oil film and decreased fuel economy. Heavy-duty engines usually operate on an oil that is 10W40 or 15W40, whereas passenger car engines usually use a 0W30, 5W30, 0W20 or 5W20 oil.

How often should I change the oil?

This depends on the local circumstances: in passenger cars, the oil needs to be changed from anywhere between 2000km and 10,000km on average and, as specified by certain European manufacturers, under ideal conditions and with approved oils, up to 30,000km. Heavy-duty machinery, on the other hand, can go for as long as 40,000km or more, before needing an oil change. This is because passenger cars and heavy-duty machines operate under different conditions; depending on the driver's habits, a passenger car may be used for short distances, often not even enough to warm the oil in the engine, and the engine may run at varying RPM. Heavy-duty machinery is more likely to operate in such a way that the engine runs at a steady RPM rate throughout an average day of use. This is why, despite handling a heavier load, the engines in HDDEO’s have longer drain intervals.

Choosing the right oil for your engine, be it for heavy-duty machines or a passenger car, can increase fuel economy, reduce wear on the engine, reduce maintenance costs and downtime and keep your engine running smoothly. Always consult the user’s manual or a specialized garage before changing the kind of oil used for your engine.