How to Test a Used Car Before You Buy It

A test drive reveals things a static inspection cannot, and a surprising number of mechanical faults are only visible once the vehicle is moving under load. The test drive is also where an impulse purchase happens, so knowing what to check in what order is what separates a useful test from a pleasant drive.

This guide covers the walkaround, the drive, and what each observation tells you.

Before Driving: The Walkaround

Start at the front corners and work around. The purpose is not to find cosmetic defects, it is to find evidence of an accident or of neglect, and those are visible before the engine is started.

Check that the panel gaps are even all the way round. A gap that is wider on one side, or a door that sits proud of its neighbour, indicates that the panel has been removed, repaired, or resprayed. Check the paint depth with a gauge if you have one, since a respray reads differently from original paint and a panel that has been filler-repaired reads differently again.

Look for evidence of accident repair in the areas that are usually repaired first and are hardest to inspect: the front bumper region, the rear quarter, and the sill. Check the underside for a kerb hit on the sills and for a scuffed subframe. Look at the tyre wear across the full width of the tread, because uneven wear indicates geometry problems that may never have been corrected.

Check the tyres for age as well as depth, from the date code, and check that all four are the same make, model, size, and construction. A single different tyre produces a pull and a wet handling difference, and it is a strong indication that a previous owner replaced one at a time.

Starting It

Start the engine and listen to it cold. A healthy engine starts quickly, catches on the first or second crank, and the idle is even from the moment it fires. Listen for the first thirty seconds, because a rattle, a knock, or a whistle that disappears once warm indicates something that is worth asking about.

Watch the oil pressure warning light. It should extinguish within a second or two of the engine firing, and a light that lingers or flickers is a genuine concern. Watch the temperature needle, which should move up to its normal operating position and stay there.

Look under the vehicle for anything that drips while the engine is idling. Check for a strong smell of fuel, coolant, or burning, and check for smoke from the exhaust. A vehicle that smokes for a few seconds from a cold start is normal; one that smokes once it is warm is not.

During the Drive: The First Few Minutes

Pull away gently onto a quiet road first, which is where a transmission fault shows itself. Then drive in stages rather than taking one continuous route, because each stage brings up a different set of faults.

Cold Stage: Warm-Up Behaviour

Watch the temperature gauge come up to operating temperature and stay steady. A gauge that climbs and then falls is normal on a vehicle with a thermostat. A gauge that reaches normal and then slowly continues climbing is not normal and should be investigated. A gauge that never reaches normal is also a fault.

Watch the oil pressure light once the engine is warm. A light that returns when the engine is hot is a genuine concern that many sellers never notice.

Listen for a knock from the engine during warm-up, which can indicate an injector or a valve issue, and listen for a whistle that appears as the engine warms, which can indicate an exhaust leak ahead of a turbo.

Low Speed and Light Load

Drive slowly in a lower gear. This is where hesitation, misfires, and irregular idling are most visible. Watch the revs: if the vehicle accelerates without the revs rising proportionally, a slipping clutch or a torque converter problem is present, and the related symptoms are covered in why a car loses power in low gears.

Steady Cruising Speed

Hold a steady speed on a straight road and check whether the vehicle tracks straight without constant correction. A pull here points to a geometry problem or a brake drag, both of which are covered in why a car feels unstable at speed.

Hard Acceleration

Do not do this in the first five minutes with a cold engine, but once it is up to temperature, accelerate firmly from a low speed in a clear area. This is where a misfire, a judder, a slipping clutch, and a fuel supply fault all become obvious. Watch the revs and watch for a stumble. The judder patterns are set out in car shudders when accelerating in low gears.

Braking

Apply firm braking on a straight, clear stretch at moderate speed. A pulsation through the pedal indicates warped discs. A pull under braking indicates a caliper drag or a geometry problem. A grinding noise means the pads are finished and the vehicle should not be driven further without addressing it. A soft or spongy pedal indicates air or moisture in the hydraulic system and is a safety concern.

Over a Bump or a Pothole

Where a suitable road surface exists, drive over a known bump. Every rattle from the suspension, the anti-roll bar links, the wheel bearings, and the exhaust hangers becomes audible. A knock from the suspension on one side is worth asking about, and a rattle from the exhaust usually means a hanger has broken.

Reversing

Reverse slowly, which is where a dragging brake is most obvious because the braking is applied and the vehicle is slow. A noise or a tendency to pull strongly to one side in reverse is a strong indicator of a seized caliper or a sticking slide pin.

Coming to a Stop

Brake gently and bring the vehicle to a halt. Then look in the mirror at the brake lights, and check that they illuminate. Watch the temperature gauge immediately after a long climb and a descent, since a cooling system fault will show there.

After the Drive

Park on level ground, leave the engine running, and check the oil level on the dipstick after a couple of minutes. An oil level that has fallen noticeably, or that is near minimum immediately after a drive, indicates consumption and is a significant warning. Check underneath again for fresh leaks, and check the coolant level in the expansion tank once the engine has cooled.

Restart the engine after a few minutes and listen to the warm start. A hesitation on a warm start that was absent on a cold start points at the fuel system or the ignition, and it is a common and informative finding.

Check the temperature gauge on the return journey. If it climbs higher after the drive than it did before, there is a cooling system issue.

Questions to Ask While You Are There

Ask about the service history and whether it is complete, because the answer tells you as much as the records do. Ask whether the vehicle has been in an accident, and if so whether it was structural. Ask why it is being sold. Ask whether any warning lights have come on. And ask whether the battery has been replaced and when.

The service history check is set out in how to check a used car service history, and the coolant and battery checks relate to why a car loses coolant and why a car battery dies in hot weather.

Commission an Independent Inspection

If the vehicle looks right and drives acceptably and you intend to buy it, that is the moment to commission an independent pre-purchase inspection rather than after. An inspection by someone with no financial interest in the sale, with the time to lift the vehicle and check the underside, the fluids, the codes, and the history, is the single most useful thing you can arrange. The questions worth asking of the inspector are in how to choose a workshop you can trust, since the same standards apply.

A test drive tells you whether the vehicle is currently working. It does not tell you whether it is about to need a cambelt, whether the cooling system has a marginal hose, or whether the head gasket is at the early stage. An inspection does, and it is the difference between buying a vehicle and gambling on one.