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Actually, 10-Year-Old Motor Oil Can Be Just Fine

Popular Mechanics logo Popular Mechanics 12/6/2018 Ezra Dyer
It's been in the ground for 100 million years. What's six more months?© Provided by Hearst Communications, Inc It's been in the ground for 100 million years. What's six more months?

You bring your car to the oil-change place and they slap a sticker on the windshield: Change it again in 3,000 miles or three months. You probably knew that the 3,000-mile interval was ridiculous, but what about that other deadline? What if you don’t drive much and let your oil sit for six months? A year? I know a guy with a fleet of Ferraris, some of them seven-­figure cars, and he goes only by mileage. “That oil was in the ground for 100 million years,” he says. “What’s six more months?”

Research

Good question, one that I recently answered through semi-intentional negligence. Here’s what happened: In 2008, I bought a Troy-Bilt lawnmower with a Honda engine. After a few years, I realized I hadn’t changed the oil. But, by then, electric mowers were getting cheap, and I really wanted an electric mower. I figured I’d just let the Troy-Bilt go until it blew up. Which it refused to do. I kept mowing my lawn, season after season, the little Honda purring away, until I eventually started feeling bad for the thing. I decided that if I pulled the trigger on an electric mower, I could at least give my Troy-Bilt to someone who would use it. I warmed it up, tilted it over, and drained the oil, saving a few ounces to send to Blackstone Laboratories, an oil-testing company in Fort Wayne, Indiana. A basic analysis costs $28.

I was particularly interested in the TBN (total base number). Oils contain bases to prevent acidification, so the TBN shows how much additive is left to keep it healthy. A TBN of less than one is considered bad. My oil’s TBN? Five. Hooray! The sample was also spot-on for average values of zinc and calcium, but a little high on sodium. Silicon was way high, about four times normal. Flashpoint was a little low, at 360 degrees Fahrenheit.

What does all this mean? Blackstone wrote it out on my oil’s report card: “Universal averages show typical wear for similar Honda engines with about 65 hours on the oil. This oil was in use for ten years, and may even be the factory fill. If so, some of the excess metal is from initial break-in and silicon could be sealer material from assembly. Silicon can also show abrasive dirt contamination, which causes poor internal wear. There’s also some fuel and moisture in the oil. The TBN is okay at 5.0, so the oil actually has additive left in reserve. Make sure the air filter is in good condition.” It still had additive, and the biggest contaminant, silicon, is probably from the initial break-in. The oil was dirty, but leaving it there for ten years didn’t really hurt anything. So, should you wait ten years between oil changes? No. But don’t worry if you miss the date on the Jiffy Lube sticker.

How To Get Your Oil Tested

A $30 analysis will tell you how long your car can really go between oil changes. Knowing to skip even one unnecessary trip to the shop makes it worth it.

Step 1: Set up for a full oil change

You could pull just enough for a sample, but the results might over-represent the dirt lurking around the drain.

Step 2: Warm up your engine

Halfway through, funnel a three-ounce sample into your bottle.

Step 3: Drain your oil

This cooks off any fuel and gets the oil flowing. Have a clean container ready. I used an empty water bottle-dry, of course.

Step 4: Make sure there are no leaks

In Blackstone’s case, you wrap the sample jar in absorbent material, zip that in a plastic bag, then put that in a larger plastic container, which you also seal. That one has a prepaid USPS sticker on it, so off it goes-maybe. Oil is not a hazardous material, but some post offices might give you guff about sending it. Refer them to USPS Publication 52, “Hazardous, restricted and perishable mail.” Or just put your sample in a box.

(Editor's Note: We don't recommend using 10-year-old motor oil)

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