Motoring Q&A: A closer look at synthetic oils
Q: I use fully synthetic oil because it lasts twice as long as the regular stuff and I read that, because it doesn’t cause varnish build-up in the cylinder walls, it reduces engine wear. It’s my understanding I can use this oil for up to 15,000 miles, though I know the filters need to be changed more frequently, perhaps every 10,000 miles or so. What are your thoughts on those mileage figures and the subject of synthetic oil in general?
A: First of all, synthetic oils don’t “last longer” than petroleum lubricants. In fact, neither type actually wears out. What does happen, is that engine components, over time and mileage, consume additives in the oil. Also, and more important to my way of thinking, contamination occurs. Combustion byproducts, fuel, moisture and particulate debris accumulate in engine oil. Additives like detergents, dispersants and viscosity improvers are effectively “used up” during the lubricant’s service life.
Full-flow oil filters, which filter all oil as it circulates through the engine, only trap solids roughly 20 microns or larger, meaning that smaller particulates continue to circulate in the oil. A micron is one-millionth of a meter. Putting this into perspective, a human hair is as small as 30 microns thick. While oil filters do a remarkable job of filtering debris, they cannot and do not filter out soluble contaminants like fuel and water.
Motor oil filters are required to balance filtration versus flow. Finer filtration — say, 10 microns or less — could lead to a lack of oil flow in cold weather causing potential engine failure.
I agree that chemically built synthetic lubricants provide better lubrication performance than petroleum oils, particularly in extreme conditions such as cold starts, high-temperature operation and sustained high engine output. But only by a small margin. Carmakers publish their oil change interval requirements without distinguishing between natural and synthetic lubricants. The API service rating for motor oil doesn’t make the distinction either. And yes, some carmakers call for the use of synthetic lubricants in their engines.
Add to the equation the fact that modern technology, including design, electronics, metallurgy, manufacturing and assembly techniques, deliver high-quality engines with much greater durability and reliability, and it is no longer uncommon for automotive engines to deliver 150,000-200,000 or more reliable miles.
So yes, oil change intervals have lengthened significantly. But the fact that carmakers distinguish between “normal” and “severe service” operation confirms that lubrication qualities — not the oil itself — is influenced by time, mileage and operating conditions. That’s why oil service monitoring systems calculate oil change recommendations rather than suggesting specific mileages.
On the other side of the issue is the simple fact I continue to focus on: It is my name on the title. I’m the one responsible for maintaining the vehicle — not the carmaker. I see my more frequent oil change intervals — roughly 5,000 miles — as a low-cost insurance policy to protect against potential engine problems.
According to the AAA, the average annual cost of owning, operating, fueling, depreciation, licensing, insurance and maintaining a late model automobile is approximately $9,000. Spending $50 four times a year for oil changes is, at most, about 2 percent of the total. Cheap insurance, for sure.
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