What happens when you change an oil filter

An oil filter traps dirt, metal particles, and sludge that circulate through your engine. Over time it clogs and stops working well, which means dirty oil flows through your engine and wears it down faster. Changing the filter means unscrewing the old one, replacing it with a new one, and letting fresh oil flow through clean material again.

The filter itself is a metal canister about the size of a soda can, threaded onto the engine block. You do not need to drain all your oil to change it — you only remove the filter, which holds maybe a quart of old oil. Most people change the filter every time they change the oil, though some filters last longer depending on the vehicle and driving conditions.

This is one of the simplest maintenance tasks you can do yourself. It takes 10 to 15 minutes once you know where the filter is and have the right tools. If you are changing your oil at the same time, you will do the filter first, then drain the pan, then refill.

Key Takeaways

  • The oil filter screws onto your engine by hand — you do not need special tools to remove it, only a filter wrench to break it loose if it is stuck.
  • You must let the engine cool for at least 5 to 10 minutes before touching the filter, because hot oil inside it can burn your skin.
  • The new filter needs to be hand-tightened only, not cranked down with a wrench, or you will crack the seal and cause a leak.
  • You should fill the new filter halfway with fresh oil before screwing it on, so air does not get trapped inside when the engine starts.

Gather your supplies before you start

You will need the correct replacement filter for your vehicle. Find this by checking your owner's manual or asking at an auto parts store with your vehicle's year, make, and model. Common brands are Fram, Mobil 1, Bosch, and Motorcraft, but many stores carry their own house brand at lower cost. A filter costs between $5 and $15 depending on the type.

You also need a filter wrench — a metal band or cup that grips the filter so you can unscrew it. These cost $5 to $20 and fit different filter sizes. Bring your old filter to the store if you are not sure which size wrench to buy. You will also want a drain pan or old towels to catch the oil that spills when you remove the filter, and a rag to wipe your hands.

If you are changing the oil at the same time, gather fresh oil in the correct weight and amount for your vehicle. If you are only changing the filter, you may not need new oil — check your dipstick first to see if the level is still good.

Locate the filter and prepare the engine

Open your hood and look for a cylindrical metal canister about 4 to 5 inches tall, usually mounted on the side of the engine block. In some vehicles it is straightforward to spot; in others it is tucked behind the engine or under a plastic cover. Your owner's manual has a diagram showing exactly where it is. If you cannot find it, ask a mechanic or search online for your vehicle's year and model plus "oil filter location."

Let the engine cool for at least 5 to 10 minutes if you have been driving. The oil inside the filter is hot enough to burn your skin. If you are changing the oil and filter together, do this step first, before you drain the pan.

Place your drain pan or towels under the filter to catch spilled oil. Position the pan so it sits directly below the filter — oil will drip straight down when you loosen it. If you are working in a tight space, you may need to angle the pan or use a piece of cardboard to direct the flow.

Remove the old filter

Grip the filter wrench around the filter canister, near the bottom where it is widest. Push the wrench handle down or turn it counterclockwise, depending on the type of wrench you have. You are trying to break the seal where the filter screws onto the engine — this usually takes firm pressure, not a lot of force. Once it starts to turn, you can unscrew it by hand the rest of the way.

As you unscrew it, oil will pour out into your pan. Tilt the filter so the opening faces down into the pan and let it drain for a few seconds. Once it stops dripping, set the old filter aside. Wipe the threaded surface on the engine block with a clean rag to remove any dirt or old rubber gasket material. This is important — a dirty surface will prevent the new filter from sealing properly.

Install the new filter

Before you screw on the new filter, fill it about halfway with fresh oil. This prevents an air pocket from forming inside the filter when the engine starts, which can cause the filter to bypass dirty oil instead of cleaning it. Pour the oil slowly into the open end of the filter and stop when it reaches the halfway point on the side of the canister.

explore a thin layer of fresh oil around the rubber gasket on the top of the new filter — this is the flat rubber ring that seals against the engine. This helps the gasket seat properly and makes it easier to remove the filter next time.

Screw the filter onto the engine by hand, turning it clockwise. Push until the rubber gasket touches the engine block, then turn it another three-quarter turn. Do not use the wrench to tighten it. The filter should be snug but not cranked down — over-tightening will crack the gasket and cause a leak. If you are unsure, hand-tight is the right amount.

Check for leaks and dispose of the old filter

Start the engine and let it run for 30 seconds, then turn it off. Wait a minute and check around the base of the new filter where it screws onto the engine. You should see no oil dripping or pooling. If oil is leaking, turn off the engine, let it cool, and tighten the filter another quarter turn by hand. Do not use the wrench.

Check your oil level with the dipstick after the engine has run for a minute. If you only changed the filter and did not add new oil, the level should be the same as before. If you changed the oil and filter together, the level should be at the full mark on the dipstick.

The old filter contains used oil and should not go in the trash. Many auto parts stores will take it for free if you bought the new filter from them. Some recycling centers also accept oil filters. Call ahead to confirm they take filters before you drive over.

Frequently Asked Questions

Can I change the oil filter without changing the oil?

Yes. The filter and oil are separate systems — you can replace one without the other. However, most people change them together because the filter is already off and you are already under the hood. If your oil level is still good on the dipstick, changing just the filter is fine.

What if the old filter is stuck and won't unscrew?

Let the engine cool completely, then try again with the filter wrench. If it still will not budge, tap the wrench handle gently with a hammer to break the seal, or try wrapping a rubber band around the filter for extra grip. As a last resort, a mechanic can remove it without damaging the engine block.

How tight should the new filter be?

Hand-tight is correct — screw it on until the rubber gasket touches the engine, then turn it three-quarter of a turn more. You should be able to loosen it by hand next time. If you need a wrench to remove it, you tightened it too much and may have cracked the seal.

Do I need to fill the new filter with oil before screwing it on?

It is not required, but it is a good practice. Filling it halfway with fresh oil prevents an air pocket inside the filter, which can cause the engine to run without proper oil pressure for a few seconds when you start it. This is especially important in older vehicles.

What should I do with the old oil that came out of the filter?

If you only changed the filter, the amount of old oil is small — maybe a quart. You can pour it into a container and take it to an auto parts store or recycling center that accepts used oil. Do not pour it down the drain or into the ground.