Motor oil: How thin is too thin?

Ron Nutini is a licensed automotive technician in Trail

If you are driving a late model four cylinder Toyota Camry you may have noticed that the required engine oil is a multigrade 0W16. That is one thin oil! Why so thin?

The viscosity of a liquid refers to the resistance to flow. Low viscosity (smaller number) flows easier than high viscosity (higher number). Almost all vehicles require a multigrade engine oil. The multigrade means that the oil behaves like two different oils at two different temperatures. The standards developed for grading motor oils was developed by the SAE (Society of Automotive Engineers). Any of us who have purchased engine oil usually requested a particular viscosity of oil. I buy 10w30 for my American V8 and 5W20 for my Asian V6.

The number 10W in 10W30 refers to the viscosity of the oil at winter temperatures. Cold starts require thinner oil to slip between all the cold moving parts. But as the temperature rises in the engine that oil cannot thin out too much or there will be metal to metal contact and wearing parts. As 10W30 engine oil warms up the viscosity of the oil decreases but the decrease is reduced to that of a 30 viscosity oil at 100 degrees Celsius. Yes, the oil is less viscous at the higher temperature but more viscous than a normal 10W oil would be. Yes, it is kind of a magic trick by petroleum engineers.

In my mind I was always a thicker is better in the oil department. I had a hard time putting 5W20 engine oil in my Honda V6. Would thinner oil not burn faster and provide less protection for all those fast moving parts? My 1969 VW beetle got 20W50. Nothing less.

Well the engineers wanted 5W20. I trusted them. Not sure why, but my Honda is still alive with 300,000 kilometres under its belt.

What is the driving force behind automobiles using thinner oils? Increased efficiency! Thinner lubricants create less drag on all the moving parts. Less drag means less energy wasted which equates to higher fuel efficiency and more power to the wheels.

Modern thinner motor oils have improved properties to prevent wear. Modern engine machining means part clearances can be tighter and the surface finish of materials are better. Tighter clearances require thinner oil to move freely between the myriad of moving parts. Thinner oil cools better than thick oil and engines designed to work with thinner oils also require the thin oil to help with keeping the engine cool.

Won’t a thinner engine oil burn more easily? Yes, generally it would but again the properties of these new thin motor oils are such that they work as designed. Again the engines and engine oils are designed as a package. Technology moves on.

Can I accept 0W16 motor oil? I guess I will. In Japan they already use 0W8 engine oil.

Trail’s Ron Nutini is a licensed automotive technician and graduate of mechanical engineering from UBC. E-mail: nutechauto@telus.net

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