How often should you change your synthetic oil in months

You bring your car to the auto repair shop and they slap a sticker on the windshield: change your oil 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?

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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?” That’s a good question, and 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.

“The oil was dirty, but leaving it there for 10 years didn’t really hurt anything.”

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 higher than normal. Flashpoint—the temperature when the oil’s vapors ignite, which can signify a contaminant like fuel in the oil—was a little low, at 360 degrees Fahrenheit.

Long story short: the oil was dirty, but leaving it there for ten years didn’t really hurt anything. What does that 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.”

So, should you wait 10 years between oil changes? No. But don’t worry if you miss the date on the Jiffy Lube sticker.

Why Do Repair Shops Say I Should Change My Oil So Dang Often?

Your average 3,000-mile quickie-lube sticker gives you a general suggestion of when to change your oil based on a really severe maintenance schedule. Their job is to sell oil changes, after all. The real authority you should consult first—if you’re erring on the side of caution and not in the market for a new lawnmower—is the owner’s manual for your vehicle. Different vehicles have different maintenance needs, especially with recent advances in automotive technology that have pushed some newer cars’ oil change intervals out to 7,500 or 10,000 miles, or once every six to 12 months.

Why Are Oil Change Recommendations Given in Mileage and in Time?

Oil degrades over time. The longer it sits, the less viscous it becomes and thus, the less effective it will be at keeping various engine components properly lubricated. Synthetic oil is designed to break down more slowly over time, which means you can probably stretch its oil changes out a little longer, but it still breaks down like any other oil. Oil that degrades too much can cause engine sludge that can block oil flow entirely.

How Often Should You Change Your Oil?

Even if you don’t drive very often and you’re not hitting the recommended mileage interval, it's bestto get your oil changed twice a year. Your oil may be fine, but it’s the moisture in your engine that’s the real enemy. If you don’t run your car for very long very often, the engine won’t get hot enough to burn off this moisture, and your oil won’t be as effective at lubricating your engine, eventually leading to shorter engine life.

What Is a “Normal” Vs. “Severe” Maintenance Schedule for Oil Changes?

Remember how we keep calling the quick lube’s usual suggestion “severe?” Owners’ manuals often list both a “normal” and a “severe” maintenance schedule, with the latter being for harder driving, extreme weather, and other cases where there’s extra stress per mile on the engine, such as hauling heavy loads, towing, and track day use.

This is bad news for your grandparents’ couple-blocks-to-church use case: never getting the engine warm enough to burn off any condensation inside is also considered “severe” use. It typically takes about 10 miles to burn off that moisture, so if trips over 10 miles are rare-to-never, follow the “severe” schedule until you can get an expert analysis done.

How Can I Check My Oil?

Few things beat simply pulling the dipstick out of the engine for a visual check. Even new cars can consume a little oil and may need topping off, so this is a good idea to do about once a month anyway. Taking a look at the dipstick can also give you an idea of when you should change your oil based on your driving habits.

Look for common warning signs of engine damage while you’re peeking at your dipstick. If your oil looks lighter or cloudier than usual—frothy like latté foam in extreme cases—you may have coolant leaking into the engine, perhaps from a broken head gasket. Watch out for any glittery chunks of metal, too. That usually signifies internal engine damage, potentially from metal parts not getting lubricated well enough. Either way, if your oil looks a little too glittery for comfort or smells too much like another fluid (such as coolant), that’s a good time to get an oil analysis done to determine how that may have happened.

How To Get Your Oil Tested

An oil analysis will tell you how long your car can really go between oil changes. They’re cheap, too—Blackstone’s standard analysis is just $30, and can tell you if you’re changing your oil too often or not often enough. Knowing to skip even one unnecessary trip to the shop makes it worthwhile.

➡️ Step 1: Set up for a full oil change

Don’t change your oil just yet! You need to pull your sample from your dirty oil, after all. Wait to finish your oil change until after you’ve pulled a sample.

➡️ Step 2: Warm up your engine

Warming up your engine’s oil helps circulate your oil one last time, heating the oil so it can flow more freely out of your oil drain plug.

➡️ Step 3: Drain your oil and take your sample

You could pull just enough for a sample, but the results might overrepresent the dirt lurking around the drain. Instead, be sure to take your oil sample sample mid-flow to get the best representation of what’s in your oil pan. 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 Office locations might give you guff about sending it. Refer them to USPS Publication 52, “Hazardous, restricted and perishable mail.” Alternately, just put your sample in a box.

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Ezra Dyer is a Car and Driver senior editor and columnist. He's now based in North Carolina but still remembers how to turn right. He owns a 2009 GEM e4 and once drove 206 mph. Those facts are mutually exclusive.

Stef Schrader routinely breaks and attempts to take project cars on race tracks. She enjoys fancy cheeses, good coffee, fast Porsches, traveling to new places and rare, weird cars. She lives with a large collection of Fisher-Price Puffalumps and an overloaded parts shed.

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