If you’re familiar with the “three months or 3,000 miles” oil change advice, you’re a little out of date. Depending on the oil quality, the car in question, and the driving conditions you normally deal with, you may be able to wait anywhere from 5,000-10,000 miles between oil changes. Toyota, for instance, recommends sticking with synthetic oil and changing it every 10,000 miles or 12 months.
However, just because you don’t have to change your oil as often as you might have thought doesn’t mean you should be avoiding it altogether. There’s a lot that can go wrong if you aren’t sticking to the schedule:
The purpose of engine oil is lubrication, which keeps the metal engine parts moving smoothly against each other, instead of regularly grinding tiny pieces off each other. It also keeps the engine clean by washing away the tiny particles of dirt that get past the air filter and the gasoline residue left in the cylinders. The main reason oil goes bad is because it picks up too much dirt, much the way a mop only cleans up so much dirt before it starts spreading it around instead.
One of the main reasons that you want to get the dirt out of the engine cylinders is that it can scrape the metal and wear down the most important and irreplaceable parts of your engine. If this goes on long enough, metal flakes will also start to build up in the oil, adding to the problem.
Oil isn’t the only ingredient in the bottle you add to your reservoir. Like spices in a soup, additives are what make the engine oil do its best, avoid burning, and maintain the perfect viscosity even when you start your engine in the middle of winter. There was a time when you needed to use different oil weights for summer and winter, but thanks to modern additives, one oil can handle it all. However, these additives tend to break down over time and, as a result, the oil becomes much less effective.
Between the loss of additives and the increase in dirt, old oil will turn into sludge and slowly stop lubricating your engine entirely. If you avoid changing your oil long enough for this process to reach its natural conclusion, your engine will seize up completely. The resulting heat will cause the moving parts to melt together, forming a useless block of steel that will cost thousands upon thousands of dollars to replace. In fact, replacing an engine can be so expensive that in many cases it’s cheaper just to buy a new car.
So while you don’t have to change your oil every three months anymore, the bottle you start with is not going to last the lifetime of your vehicle. And don’t forget your dipstick: you can find out how old your oil is at any time by wiping your dipstick on a paper towel and checking to see whether it’s turned black.
