Fresh oil keeps the engine’s moving parts from grinding on each other. Old oil gets dirty and thin, and the engine wears faster. How often depends on your car and the oil it uses.
Many modern cars on synthetic oil go 5,000 to 10,000 miles (8,000 to 16,000 km) or 6 to 12 months, whichever comes first. Older cars or those on conventional oil often want it sooner. Your owner’s manual gives the exact figure, and many cars have an oil life monitor on the dashboard that does the math for you.
Mostly short trips, towing, very hot or cold weather, and stop-start traffic are all harder on oil. If that’s you, change it towards the short end of the range.
Changing oil at home is manageable with the right tools, but you need a safe way to lift the car, and a place to dispose of the old oil properly. A shop is quick and also checks other fluids.
Even if you drive very little, oil ages. Most makers say change it at least once a year. Check your manual.
Usually, yes. It resists heat and breaking down better than conventional oil, which is why synthetic intervals are longer.
Sludge builds up, parts wear faster, and in the worst case the engine can fail. It is one of the cheapest ways to protect your car.
General guidance, not professional advice. Intervals are typical ranges and vary by car, so check your owner’s manual and ask a qualified mechanic if you’re unsure.