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What Would Happen If I Never Changed the Oil in My Car?

Would the car slow down? Stop running? Explode? What’s this stuff for, anyway?

Everyone knows what oil does to a car… Uh… Right? Something about… [checks internet] …lubricating the engine? Well, whatever the hell it does, everyone seems to grasp that it’s somehow vital to keeping an engine running. But how vital is it exactly? What happens if you never change your car oil? Would your Honda spontaneously erupt into a fireball like in an action movie, or what? 

To help answer this, I dropped by my local auto garage, armed with some mildly dumb — okay, very dumb — questions. San Diego’s Cliff Brown Automotive is a total throwback: Unlike at the branded dealership service center, there are no young guys running around plugging computers into a car engine. Cliff’s car bays are always full of an intriguing combination of classic whips, vintage matte-finish pickups, late-model muscle cars, company trucks and government vehicles — and the small, wood-paneled office nostalgically smells of freshly burned cigarettes. It was here that mechanic Barry Y., the general manager, patiently explained what all this motor oil business is about.

So first things first, what oil does for an engine: Yep, lubrication. There are a bunch of moving parts in an engine, and the oil is a barrier between them that helps keep them moving smoothly — much like C3PO’s spa treatment in A New Hope. It doesn’t take a genius, then, to imagine a hot engine without good oil in it probably wouldn’t be running at all. “It builds friction to the point of the engine ceasing, which would cost a lot of money to fix!” Barry says.

Makes sense so far. So about those oil changes — what happens if you don’t change the oil and it starts turning black? 

The blackness is actually soot, and slowly builds up as a result of incomplete combustion. When your oil starts to sludge, bad things happen to your engine, Barry says. Namely, at the bottom of the oil pan there’s a pickup screen, which leads to the pickup tube. All your oil passes through that screen prior to running through your oil filter and then throughout your engine. And if that screen plugs up with debris, you’re going to lose oil pressure. “And when you lose oil pressure, that’s when you have loss of lubrication of the internal parts,” Barry says. It’s kind of like what a steady diet of Meat Lovers pizza will inevitably do to your body’s arteries and blood circulation over time.

Obviously, this sounds bad! But can not changing the oil actually destroy your engine? How long would it take for your car to stop running? 

According to Barry, not too long. “If you never, ever changed your oil and you’ve got sludge buildup and your passages are blocked off… Let’s say you have a 100,000-mile lifespan on an engine,” Barry says. “You can cut the life of the engine in half just because you never changed your oil.”

And here’s where things get interesting: He says an older motor would actually last longer in this (hopefully hypothetical) scenario. That’s because new engines are built with much smaller tolerances than before, meaning there’s a tiny amount of space between the moving parts. There’s something else, though. “Older engines last longer, and they’re built better than the newer motors today. I’m serious as a heart attack!” Barry says. Just like with everything else these days — say, refrigerators and washing machines — they’re built so cheaply yet are so expensive to fix that, when some stupid sensor stops working, it’s often cheaper to just buy a new one and throw the old one away.

What Happens If You Never Change Your Oil

Well, the car wouldn’t explode, but the engine would eventually seize up. The engine’s cylinder head, as well as the engine block, are all made of aluminum, and they’ll suffer damage to the inner cylinder walls or the crankshaft. “So basically, a lot of times you just throw that motor away, call the dealer, get another motor,” Barry says. “Or if the customer doesn’t have that kind of money, see if you can find a good used one at a wrecking yard.”

It’s more common than you think — at least, the sludge is. Even though many of his customers are regulars, Barry says he still sees probably 10 percent of all cars coming in with sludge issues.

Let’s back up a bit, though: That whole sludge thing is worse than people might imagine. Once the oil starts sludging, your engine is already somewhat ruined, per Barry, because you can’t fully get it out. There are chemicals that break up the sludge particles off the engine block, but then it gets sucked up against that pickup screen in the oil pan, which blocks the oil flow. “Once you got sludge, the damage is done,” he says. 


So we now know what happens if you never change your oil. But how often should you do it? As frequently as your carmaker says? Actually, probably more. Barry says the manufacturers are crazy for telling car owners to only change the oil every 10,000 miles on newer cars. He stresses that this is his opinion, but nevertheless: “Depending on the type of driving you do, and especially in California where there’s a lot of traffic, stop and go, and high speeds, I recommend changing with full synthetic oil every 5,000 miles,” he says. “Whereas if you look at a new car’s maintenance schedule it says every 10,000. Which is ridiculous!” 

In short, change your damn oil! Your engine will be irreversibly damaged if you procrastinate about it, and will literally break if you never get around to it. All of which is a much bigger hassle than the oil-change center trying to upsell the shit out of you every visit.