Oil changes are often recommended when a certain mileage or time limit is reached. The most
familiar interval is 3,000 miles or three months, but what’s more important — the mileage or
the time?

Experts say trust the odometer, not the calendar. Driving has far more of an impact on your engine oil; if a car is sitting, there is less need to replace the engine oil. Oil-change intervals used to be much more frequent than they are today. Around 50 years ago, you would have had to change your oil every 500 miles. Today, the drain intervals for some oils dwarf even the 3,000-mile standard, with some special performance oils recommending changes at 15,000 up to 35,000 miles.

Where and how you drive can influence how often you need to change your oil. Factors include extreme heat, towing a trailer and driving where there’s dust and sand.

In short, it’s not pretty.

One of the problems is that there will begin to be buildup in the cooler parts of the engine, like the crankcase and around the camshafts and valves. This can lead to carbon deposits, or sludge, coming out of the old oil. That could require an expensive engine cleaning or force you to replace worn-out piston rings.

It can get worse. The pistons could eventually seize or the camshafts could be damaged. Getting a bill for either one of these repairs would make even a few high-quality oil changes look like pocket change. Consider regular oil changes to be like really cheap insurance for your engine.