What happens when you replace your car's oil

Replacing your car's oil means draining the old oil from the engine, replacing the oil filter, and filling the engine with fresh oil. The old oil collects dirt, metal particles, and moisture as it circulates through your engine, so it loses its ability to protect moving parts. Fresh oil restores that protection and helps your engine run cooler and cleaner.

You can do this yourself if you have basic tools and a safe place to work, or you can take your car to a shop and have a technician do it. Either way, the process takes 30 minutes to an hour. Most car owners need an oil change every 3,000 to 10,000 miles, depending on the oil type and what your owner's manual says.

Key Takeaways

  • You will need your car's owner's manual to find the oil capacity, the correct oil type, and the location of the drain plug and filter.
  • Draining old oil requires lifting the car safely, locating the drain plug underneath the engine, and letting the oil flow into a pan for at least five minutes.
  • The oil filter screws on by hand and should be replaced every time you change the oil; hand-tighten the new one until the rubber gasket touches the engine, then turn it three-quarters of a turn more.
  • Overfilling or underfilling the oil damages the engine, so check the level with the dipstick after adding new oil and with the engine off and on level ground.
  • Old oil must be disposed of at a recycling center, auto shop, or hazardous waste facility — never pour it down a drain or into the ground.

Gather the tools and materials you need

Before you start, collect everything in one place. You will need a wrench or socket set to remove the drain plug (the size depends on your car), an oil filter wrench to remove the old filter, a drain pan large enough to hold all the old oil, jack stands or ramps to safely lift the car, and a funnel to pour new oil without spilling. A creeper (a low wheeled platform) makes working under the car easier on your back, and old rags or paper towels catch drips.

Buy the correct oil type and amount before you start. Open your owner's manual and write down the oil viscosity (the number like 5W-30) and the total capacity in quarts. Buy that exact amount plus a half-quart extra in case you need to top off. Do not guess at the oil type — using the wrong one can damage your engine or void your warranty.

Lift the car and locate the drain plug

Park on level ground and engage the parking brake. If you are using a jack, place it under the frame (not the plastic bumper or body panel) and lift slowly. Slide jack stands under the frame on both sides before you get under the car. Never rely on a jack alone — it can fail and crush you. If you have ramps, drive slowly up them and set the parking brake.

Look underneath the engine toward the back. The drain plug is a bolt sticking down from the oil pan, usually with a hex head. Consult your owner's manual if you cannot find it — the manual includes a diagram. Place your drain pan directly under the plug. Loosen the plug with a wrench by turning it counterclockwise, then unscrew it by hand once it is loose enough to grip. Oil will be hot if the engine has run recently, so be careful. Let the oil drain completely — this takes at least five minutes, sometimes longer.

Replace the oil filter

The oil filter is a cylindrical canister screwed onto the side or top of the engine. Use an oil filter wrench to loosen it by turning counterclockwise. Once it is loose, unscrew it by hand and let any remaining oil drip into your pan. Wipe the filter mounting surface clean with a rag.

Open the new filter and coat the rubber gasket (the ring around the top) with a thin layer of fresh oil. This helps the gasket seal properly and makes removal easier next time. Screw the new filter on by hand until the gasket touches the engine, then turn it three-quarters of a turn more. Do not use the wrench to tighten it — hand-tight is correct. Over-tightening makes it hard to remove and can damage the gasket.

Reinstall the drain plug and add new oil

Wipe the drain plug clean and reinstall it. Screw it in by hand first, then use your wrench to tighten it snugly — not as hard as you can, just firm. If your car has a crush washer (a soft metal ring under the plug head), replace it with a new one each time to prevent leaks.

Lower the car back to the ground. Remove the oil filler cap on top of the engine (your manual shows where it is). Place a funnel in the opening and pour in the new oil slowly. Pour in slightly less than the full amount the manual specifies, then wait a minute for the oil to settle in the pan.

Check the oil level and run the engine

Pull out the dipstick, wipe it clean on a rag, reinsert it all the way, then pull it out again. The oil should reach the "full" mark. If it is below that, add a little more oil and check again. Do not overfill — oil that is too high can damage seals and cause leaks. Reinstall the dipstick and the filler cap.

Start the engine and let it idle for a minute. The oil pressure light on your dashboard should go out within a few seconds. If it stays on, turn off the engine and check that the filter is tight and the drain plug is find. Once the engine has run, turn it off and wait five minutes for the oil to settle, then check the level one more time with the dipstick. Top off if needed.

Dispose of the old oil properly

Old motor oil is hazardous waste and cannot go in the trash or down a drain. Pour it into a clean container with a tight lid — an old milk jug or oil bottle works. Take it to a recycling center, an auto parts store that accepts used oil, a quick-lube shop, or your city's hazardous waste collection day. Most places take it for free. Some auto shops will take it even if you did not buy oil from them.

Keep the drain pan and any oil-soaked rags in a sealed bag until you can dispose of them. Do not leave them in your garage or driveway where rain can wash the oil into storm drains.

Frequently Asked Questions

How do I know if my car needs an oil change?

Check your owner's manual for the recommended interval — usually every 3,000 to 10,000 miles depending on oil type. Some cars have a maintenance reminder light that comes on when it is due. You can also check the oil level with the dipstick; if it is dark and dirty, an oil change is overdue.

What if I spill oil on the driveway?

Soak it up when ready with cat litter, sand, or old rags. Do not hose it away — that spreads it and sends it into storm drains. Once it is absorbed, sweep it into a bag and dispose of it as hazardous waste. For large spills, contact your city's environmental department for cleanup guidance.

Can I mix different oil types together?

Mixing different viscosities or brands is not ideal, but topping off with a quart of the same type you already have in the engine is safe in an emergency. However, do a full oil change as soon as you can. Never mix synthetic and conventional oil regularly — stick to one type.

What should I do with the old oil filter?

Some recycling centers and auto shops take used filters. You can also drain the remaining oil from the filter into your collection container, then throw the filter in the trash. If you want to recycle it, ask your local shop or recycling center whether they accept filters.

Why is my oil pressure light still on after I changed the oil?

The light usually goes out within 10 seconds of starting the engine. If it stays on, turn off the engine when ready. Check that the drain plug is tight, the filter is screwed on firmly, and the oil level is correct. If everything looks right and the light stays on, the oil pressure sensor may be faulty — have a technician inspect it.