A used car is one of the bigger purchases you'll make this year. The costly mistakes usually happen before anyone opens the hood: no report pulled, no structured walkthrough, no test drive that would have shown the problem.

This isn't a full mechanical inspection, and it won't catch everything. It's what you can check yourself, in about 20 minutes, before you decide whether the car is worth paying a shop to look at properly.

Before you go

Run a Carfax or AutoCheck report on any car you're seriously considering. It won't show private maintenance history, but it flags title problems, odometer rollbacks, reported accidents, and rental or fleet history.

Check the asking price against comparables (KBB, CarMax, and local listings for the same year, make, model, and mileage) before you're standing in the driveway.

Walk around it first

Stand at the corner of the car and sight down the body line. Gaps between the hood, doors, and fenders should be even. Uneven gaps usually mean prior collision repair.

Check the paint in daylight. Color mismatch between panels, overspray on the rubber trim, or a texture change from one panel to the next points to repaint work, which can mean hidden accident damage.

Check the wheel wells, door bottoms, and frame rails for rust. Surface rust on underbody parts is common and not a red flag by itself. Rust that's eaten through a frame rail or a body panel is.

Under the hood

Oil should run dark amber to brown. Black sludge is a sign it hasn't been changed on schedule; milky oil can mean coolant is getting into the engine, worth having a mechanic check for a head gasket problem before you buy.

Check coolant through the reservoir only, never by opening a cap on a hot engine. It should look clean, not rusty or cloudy, and match fresh coolant for that make (color varies by manufacturer and coolant type, so don't rely on color alone).

With the engine off, check the serpentine belt for cracking or fraying, keeping hands clear of the belt and any fans. If the car uses a timing belt, ask when it was last replaced; that's information the seller should have, not something you can see.

The test drive

Before you get behind the wheel, run the VIN through NHTSA's recall lookup at nhtsa.gov/recalls. Recall repairs are free through an authorized dealer, though eligibility can depend on the vehicle's age. If anything comes back with a "do not drive" warning, don't test drive the car until that's fixed.

Ask to start the engine cold, before anyone else has driven it that day. A cold start shows rough idle or odd noises that a warmed-up engine won't show you. If the oil pressure warning light stays on after starting, shut the engine off and don't drive the car until that's checked. If the car's already running when you get there, ask about it.

Find a clear, empty area and brake progressively: start gentle, then firmer only if the pedal feels firm and the car tracks straight. Stop the test if anything feels off. At highway speed, listen for humming that gets louder as you go faster, which often means a wheel bearing, and check that the transmission shifts without hesitation or a hard clunk.

The one non-negotiable

Whatever the walkthrough turns up, have an independent mechanic run a full pre-purchase inspection before you commit, one you choose, not the seller's shop. A car that looks and drives fine can still be hiding a problem this walkthrough won't catch.

If anything on this list turns up a red flag, or a price or a shop's write-up just doesn't add up, run it past us first. Free, no pressure.