Getting to know engine oils on a molecular level

By on August 27, 2014
Oil-Essentials

There is little debate that oil is the life of an engine. Certainly, reducing friction is the key purpose for engine oil, but these days it also plays a part in fuel efficiency, emissions control, metals protection, engine cooling and more. It’s interesting to look at the way that motor oil has evolved over the decades to match the needs of heavy duty trucks.

Conventional motor oil

This is the type of oil most of us grew up with, and it has some un-conventional behaviors. I remember, when I was young, checking the oil on some of our farm equipment. Confused at seeing how low it was, I’d ask my dad what happened. Did it leak out? He would tell me that the oil “fell out.”

I did not understand that term until I went off to school and discovered that conventional oil reacts to the extreme heat and other forces in the engine by thinning, or “falling out,” of viscosity. Thinner oil shows up as a low oil level on the dipstick.

All oils evaporate, but conventional oil evaporates at lower temperatures than synthetics oils. That not only causes the operator to top off oil more frequently, but also leads to unacceptable engine deposits and soot contamination.

Adding to those difficulties is the presence of a wax known as paraffin, which becomes stiff in cold weather. This makes it more difficult for diesel engines to start when the thermometer falls and causes increased wear on internal engine components.

Synthetic oil

Since conventional oils are made up of randomly shaped molecules that cause friction, engine oil manufacturers invested millions of dollars into finding a way to alter those molecules into a standard shape that reduces friction in engines. These synthetic oils offer a lot of advantages. They are more resistant to “fall out” and they offer a much higher degree of protection and lubricity. These oils maintain their viscosity even when exposed to extreme temperatures.

To ensure that the modern, high horsepower diesel engines receive adequate lubrication in extreme cold conditions, synthetics are the oil of choice. Some work well enough to allow you to extend your oil drain intervals, but exercise caution when it comes to this maintenance procedure. The best course of action is to refer to the engine manufacturer’s recommendations on oil drain intervals.

One other major reason to choose synthetics is fuel efficiency. Lower friction improves fuel economy, period! With fuel prices headed upward, an increase in fuel economy is a must. Of course the cost of the oil must be considered, but I believe the benefits offered by synthetics require serious consideration.

Recent trends

Many engine manufacturers are now moving to 10W-30 rather than the traditional 15W-40 oils. The tight tolerances, high horsepower and extreme pressure to deliver improved fuel economy are some very compelling reasons why we see a shift to a lighter weight of oil. I expect to see more engine manufacturers moving in this direction in the future.

Finally, the shift toward an environmentally friendly diesel engine has driven engine manufacturers to look at ash content and the oil’s ability to trap soot. EGR engines, aftertreatment systems and low sulfur diesel have all brought more attention to oil.

Aftertreatment systems are not very tolerant of high ash content oils, which is why we are seeing low ash oils for 2007 trucks and beyond. And with natural gas engines looming in the background, it is likely we will see another major shift in oils over the next few years.

I encourage every owner-operator to pay close attention when it comes to choosing and changing oil, based on available synthetics and engine requirements. With the cost of a modern diesel engine exceeding $40,000, it is critical to use the correct oil at the correct time.

Homer Hogg, Technical Training Manager for TA and Petro, has worked as a truck technician for more than 30 years. He is ASE Master-certified, a Daimler Certified Trainer and a member of the Nashville Auto Diesel College Hall of Fame.

About Homer Hogg

Homer Hogg, Technical Training Manager for TA and Petro, is an ASE Master-certified truck technician. His Maintenance Matters airs on Sirius XM's Dave Nemo Show twice a month.

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