MHC Kenworth Service department truck bays and technicians

What to Know Before Switching to 10W-30

Many medium and large fleets are ditching 15W-40 heavy duty engine oil for 10W-30. The most common reason for the change is the increase in fuel economy by switching to lower viscosity oil.

  • Fuel economy improvements are correlated with viscosity.
    Engine oil’s main job is to protect your truck engine. The combustion cycle creates heat, soot and acid, all of which the HDEO must mitigate. The thicker the oil, the more energy it takes for engine parts to move through it. The thinner the oil, the less drag put on the engine.
  • Don’t sacrifice wear protection for fuel economy.
    While the viscosity of a heavy duty engine oil accounts for its contribution to fuel economy, it is the composition of the base oil and additives that protect your engine from wear, soot and acid. Since 10W-30 is thinner than 15W-40, its film strength can be weaker and it can be more prone to oxidation. Therefore, high quality additives are needed to compensate for those weaknesses in order for 10W-30 to protect as well and last as long as 15W-40.
  • Not all 10W-30 engine oil is the same viscosity.
    The stated viscosity of a high definition engine oil does not represent an exact viscosity, but rather a range on the SAE viscosity scale. Therefore you could have two separate 10W-30 engine oils produce two different results in fuel economy. If you are comparing the fuel economy benefits of a 10W-30 to 15W-40, your results will vary depending on the exact viscosity of the 15W-40 oil because the 15W-40 designation can represent a range of viscosities.
  • Better fuel economy does not necessarily mean you’ll buy less fuel.
    While this may sound straightforward, many fleets are disappointed when they switch to 10W-30 and don’t see a reduction in fuel purchases. All things being equal using 10W-30 requires less fuel than using 15W-40. However, all things aren’t equal. Fuel prices fluctuate, routes change, cargo weights differ, weather changes, and driver behaviors can vary. The best way to ensure you are getting better fuel economy with 10W-30 is to develop and maintain a precise method for calculating fuel efficiency.

For more information, contact your local MHC.