Photo: Valvoline,Pennsoil,Quaker State

Blackstone Labs analyzes the contents of used motor oil to check how well engines wear over time. Earlier this month, the lab used its vast database of used oil analyses to study whether certain oil brands tend to contain more metal wear particles; the results might make you think twice before throwing down cash on performance racing oil.

Blackstone receives oil samples from thousands of people around the country interested in learning how well their engines are wearing over time—in part, to predict and avoid catastrophic damage. For example, I sent in an oil sample in, and learned that engine coolant was getting into my engine. If unaddressed, this could have ruined my bearings.

Upon receiving samples, Blackstone sends the oil through a spectrometer to learn how much of that oil—in parts per million—is made up of wear elements like aluminum (which may come from pistons or the engine case), chromium (from piston rings), iron (from cylinders, camshafts, or other parts of the valvetrain), copper (from bushings, bearings, oil coolers), lead (from bearings) and tin (also from bearings).

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What this means is that Blackstone has thousands of reports showing wear particle concentrations of certain engines using certain oil types for certain oil drain intervals. In its July newsletter, the lab decided to use this data to compare different brands, and the findings suggest that buying expensive oil may not provide much of a benefit to engine longevity.

Image: Blackstone Labs

The first engine Travis Heffelfinger (the Blackstone Lab senior analyst who authored the study) looked at was the Subaru EJ 2.5-liter engine, for which the lab has 5,234 reports completed. Those 5,234 reports are associated with oil samples that, on average, were used in the engine for 3,900 miles before draining.

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Travis then broke down those 5,234 reports by oil type, which owners tell Blackstone when submitting their samples. The second row in the table above shows that 1,321 samples were Rotella T6 5W-40, 483 were Mobil 1 5W-30, 184 were Subaru brand 5w-30, and so on.

Row three shows the average drain interval for each brand and type of oil (they’re all fairly close to 4,000 miles), and rows four through eight indicate parts per million of various wear particles.

The takeaway, Heffelfinger writes, is that despite the additive contents (rows nine through 15) being different (in part, because different brands use different additive blends that all accomplish the same goals), wear across the board seems quite uniform. He writes:

For wear metals, though, there’s not nearly as much variation. Iron is between 8 and 11 ppm all across the page, and copper is between 7 and 12 ppm for each set of averages. Other metals had even less variation, and no single oil type had the lowest level of all metals.

Because the oil drain intervals weren’t all exactly the same, Heffelfinger goes on, showing a bar chart of iron wear rate (which is known to increase in proportion to vehicle mileage) per 1,000 miles driven.

Image: Blackstone Labs

What the chart shows it that, even if you normalize the iron wear by mileages on the oil sample, the difference across the board—the lowest wear rate is 2.03 ppm per 1,000 miles, the highest is 2.58— is miniscule.

In other words, for every 1,000 miles, the Rotella T6 wears just over one half a part per million slower than the Royal Purple. As Heffelfinger writes in his report, that’s “...almost completely negligible. In a typical engine, a half a part per million of the oil in the sump is such a small quantity that you wouldn’t be able to see it without a microscope.”

To bring that point home, he says that a half a part per million of a 660,000 gallon Olympic-size swimming pool amounts to just over five cups of water, meaning “if you know it’s there, it might bother you, but realistically, you’ll never notice the difference.”

Heffelfinger crunched similar data from GM 5.3-liter V8 engines, Cummins 6.7-liter ISB engines, and Volkswagen 1.9-liter TDIs.

Image: Blackstone Labs

You can read the full analysis here. While some of the data points—like the amsoil in the tables above—seem to show less wear from one oil type versus another on a per-mile basis, Heffelfinger doesn’t think the difference is significant enough. He ultimately concludes that, in terms of wear rate, oil brand really doesn’t seem to be a huge factor, stating:

We see much more variation in wear levels from the type of engine, the time on the oil, the viscosity, the use the engine sees, etc. Whatever differences exist from oil brand to oil brand, we don’t see a lot of difference in terms of wear for most types of engines.

It’s worth noting that the data is only based solely on what owners and fleet managers have sent in to Blackstone with various drain intervals, so there are some limitations. For example, there might be a bigger difference in wear rate among brands if all of the oil samples had much higher mileage on them. Or perhaps longer oil use wouldn’t bring one brand to the forefront—we don’t really know based on the data.

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Plus, we don’t know much about the driving styles or weather conditions associated with each sample; averaging the samples will help to limit the effect of these factors, but it’s not a perfect solution.

Still, looking at wear metal contents for different engines, and breaking results up by oil type is an interesting study. And despite its limitations, the report’s conclusion really isn’t too surprising. Engine oils have to meet certain specs to be API certified, and even the cheapest of modern oils are known to do a damn good job at keeping engine wear down (modern engine designs have a lot to do with this, too).

While perhaps this study isn’t entirely exhaustive and conclusive, it supports my choice to use cheap Walmart brand oil in my old Jeeps. Plus, something tells me even it is better than what was available when the earliest version of that inline-six was first designed in the 1960s.