Things to Replace After Buying a Used Car

You have just saved a ton of money! Instead of blowing tons of cash on a brand new vehicle, you picked up a used car with a little wear and tear for a fraction of the price. Maybe you got the vehicle from a used car dealership or a guy on Craigslist or Facebook Marketplace. Maybe the car 30,000 miles and maybe it has 130,000 miles.

Regardless of where you bought your used vehicle or what condition it’s in, there are certain bits of maintenance that you should do immediately after buying ANY USED Car. In this article I will discuss the top things that I check and replace as soon as I park my “new to me” vehicle.

Hopefully, you thoroughly inspected the vehicle

First things first, before you bought the car hopefully you gave it a thorough once-over. I usually recommend to non-DIY people to have a mechanic inspect the vehicle before you purchase it, but if you regularly perform a variety of repairs on your cars it’s usually safe for you to inspect it.

You can check out a more thorough article here on things to consider when buying a used car.

Things to replace

Most of the maintenance parts I will discuss should be replaced regardless of the vehicle’s condition, however, if you inherited some major repair problems you can add those to the list as well.

Spark Plugs (Wires if applicable)spark plugs replacement

Unless the used car you just bought has really low mileage, I’m talking lower than the recommended spark plug replacement, you should change the plugs. Why? Spark plugs are extremely important to your vehicle, they are also inexpensive (couple bucks apiece), and 9.5 times out of 10 they are replaced within thirty minutes.

When spark plugs go bad they cause a variety of problems, rough idle, reduced fuel economy, engine misfires, and hard starting conditions. Not only that but running on bad spark plugs can also damage your engine.

Spark plug wires are not used very frequently anymore, typically you will find these on older vehicles from the 90s and early 2000s. The wires have for the most part been replaced by ignition coil on plugs, which are substantially more expensive to replace.

I only recommend that you replace the wires if you have them, they are inexpensive and should be changed with spark plugs anyways. The ignition coils are a different story, they are not typically replaced preventatively and I do not recommend it.

Change your fluids!

Starting off fresh with new fluids is generally the best route to take when buying used cars. You just can’t know for sure when the fluids were last changed, and sellers forget (or lie).

Oil changeengine oil replacement

I don’t care if the guy you met on Craigslist said that he changed the oil two days ago, if that stuff ain’t a beautiful amber color it’s time to change it! With the vast majority of vehicles nowadays you are going to want to put synthetic oil in. At your discretion you can likely use a high mileage oil if your used vehicles as over 100,000 on the odometer.

Coolant flush

Coolant/antifreeze should be flushed as well. Coolant plays an extremely important role in keeping your engine at operating temperature, and you don’t want to be running on coolant that’s past its lifespan. Not all vehicles take the same coolant so do a little due diligence before you dump the new stuff in.

Brake fluid

Brake fluid is also an extremely important component of your vehicle and it is commonly overlooked. In fact, drivers will often drive a vehicle for most of its life without ever having the brake fluid flushed.

So why is it important if so many people get away with not changing it? Because as brake fluid ages it becomes contaminated with particles that lower the boiling point of the fluid. Contamination eventually reduces the stopping power of the car and can even result in the brakes not working at all. In addition, as brake fluid becomes contaminated with moisture from the air it will slowly rust some of your other brake components.

The good news about brake fluid is that once it has been changed it typically only needs replacement every two years or so.

Transmission fluid

Please, please, please, if you bought a used Ford or a Dodge or any other vehicle known for transmission issues, change the fluid! Fluid replacement is necessary if the used vehicle you purchased has 60,000 miles or more.

It amazes me that I see so many people with vehicles that are known for automatic transmission problems, and yet they neglect to change the transmission fluid. The vast majority of domestic vehicles do not have “sealed transmissions” which means they are supposed to have regular transmission fluid and filter changes.

If you bought a higher mileage used car and you decide to ignore all of the other advice I give you, at least change the transmission fluid.

Check the tires

Shined up tires can hide a lot of defects that will not become obvious until you get on the road, and oftentimes not until you get on the interstate.

Make a close inspection checking the date the tires were manufactured, check the tire tread, and inspect the sidewalls for cracks.

Oftentimes you can tell if a car has been sitting for a while because the tires will have plenty of tread, but they will have cracks on the sidewalls. This is often a sign of substantial dry rot, and the tires should be replaced immediately unless you want to end up on the side of the road.

Don’t forget to check your brake pads

If your brake pads don’t have much meat left on them you might as well go ahead and change them.

Change your filters

Engine air filter, cabin air filter, and don’t forget your fuel filter!

Engine air filter

The engine air filter literally takes two minutes to change on nearly every vehicle, and it typically costs around 10 bucks. Most of these filters are replaceable, but every now and then you get a performance air filter like a K&N that only needs to be cleaned and re-oiled.

Cabin air filter

Most modern cars have cabin air filters, older vehicles from the 90s are more hit and miss. Cabin air filters are usually located behind the glove box, you will be surprised at the amount of grime and crap ends up in a cabin air filter. In my experience they are typically far more disgusting than an engine air filter. Cabin air filter replacement makes a huge difference in the air inside the vehicle.

Fuel filterfuel filter replacement

Fuel filters are another extremely important and often overlooked component. The fuel filter is located on the fuel line, typically underneath the vehicle on the driver’s side. The fuel filter ensures clean fuel is going into the engine.

Modern-day fuel injectors have tiny holes that could very easily get clogged up by any grime or dirt that is in the fuel. In addition, fuel filters that are not regularly changed can even clog when they have to much grime or dirt.

Fuel filters generally cost under $20. Although fuel filter replacement can be messy, it’s extremely easy, and should take under thirty minutes!

Things to check when the vehicle has high mileage

So for high mileage vehicles that have around 100,000 miles or more, there are a few additional things I recommend that you do.

Get some carburetor cleaner, if the idle control valve is easily accessible, remove it and clean out the valve. 99% of the time it’s an old idle control valve and it will be packed with grime and carbon. Overtime all that carbon can prevent the valve from opening and closing, therefore causing your engine to stall at idle.

Take the carburetor cleaner and some paper towels, and clean out the butterfly valve on the throttle body. The butterfly valve develops the same problem as the idle control valve, it gets coated with carbon and grime and then it has difficulty opening and closing.

Stephen Metellus

I am a BMW enthusiast and owner of! I have been repairing, flipping, and parting out BMWs for nearly ten years. I love these vehicles and I hope you will find my articles and YouTube channel helpful for whatever BMW project you have in store!

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