Through thick and thin
CITGO: Many people have what I call “viscosity fear syndrome” – they think thicker or heavier oils give better protection to the engine. In modern diesel technology, that is not true. Europe has been using 5W40 and 5W30. The U.S. Environmental Protection Agency SmartWay website urges over-the-road truckers to go with low viscosity – anything less than 15W.
EXXONMOBIL: The thinner the viscosity, the less resistance to flow it will have. The other side is if you go too thin, it will squeeze out between metal parts and won’t provide protection. It will not resist pumping at startup and move through the engine quicker.
Which is the better choice – natural (mineral oil) or synthetic?
CITGO: For a wider range of uses, a 5W40 built with synthetic base will deliver quality performance.
SHELL: Synthetics have two main benefits over mineral oils – better low-temperature performance and better high-temperature film thickness.
CHEVRON: In very cold or very hot temperatures, those are areas where I would prefer synthetics. The temperature curve is flatter with synthetics. As temperature range changes, the oil tends to remain at the same viscosity.
EXXONMOBIL: The base oil in synthetics makes it easier to achieve better starting at low temperatures. But the grade numbers mean the same, whether mineral oil or synthetic oil.
Should you change viscosities based on the seasons?
SHELL: We have customers who switch – they’ll use 15W40 in the summer and, depending where they are, they’ll switch to a 5W40 or 10W30 in the winter.
EXXONMOBIL: That’s the beauty of multi-grade oils. They are able to provide protection at lower and higher temperatures. If you pick the viscosity numbers correctly, you wouldn’t have to change oils for the season.
CITGO: There was a fleet in Chicago that discovered through oil analysis that when they departed from 15W40, they reduced their iron wear significantly during winter months by going to higher fluidity, lower viscosity oil. More engine wear can occur at startup. During startup, if you don’t have a proper oil film, you’re going to wear that engine at a greater rate.
EXXONMOBIL: Look at your application. Does it put a lot of stress on the motor, like heavy hauling? That would be more applicable to higher viscosity grades. It provides greater film between parts to stand up to more wear and tear.
SHELL: Not really, but it depends on the ambient temperatures.
CITGO: Pulling heavy loads doesn’t require a specific oil or viscosity. That’s the perception, but it’s not true.
What is the best solution for cold starts?
CITGO: If an oil doesn’t flow well below 15 degrees, you’re going to increase wear, put more stress on the starter and more stress on the batteries. The more you crank the engine, the more you’re going to shorten the starter life, and pulling a battery below 80 percent of its capacity, you’ll shorten battery life.