The test drive: what to check, and in what order

Two questions belong on the phone, not in the car park. First: is the car registered and insured, and does the insurance cover a drive by me? With a private seller, any driver using the car with the keeper's permission is normally covered, but the terms vary and the keeper ought to know his. Second: who bears any damage during the drive, and what is the excess?

With a dealer this is settled; he will ask to see your licence and has cover for test drives. With a private seller it is not settled, and that is exactly why the question belongs beforehand — not out of formalism, but because an open question after an incident is an argument both sides lose.

And the third precondition: the engine must be cold. Arrange the appointment so the car has stood for hours, and say so. A seller who has “just warmed it up for you” has taken half the drive away — in which case you reschedule rather than drive.

A usable test drive lasts twenty to thirty minutes and contains five kinds of road, because each makes something different audible. Leave it to the seller and you drive the loop he knows, which in experience contains no bad surfaces. Look at the area on a map beforehand and propose the route rather than being given one.

Radio off, a window open a crack, the fan on its lowest setting. Anyone talking during the drive hears nothing; which is why a companion who asks the questions while you drive is useful. And drive the last few minutes slowly again with the engine warm, because some noises appear only when warm and others only when cold.

Drive a tight figure of eight at walking pace, both ways, on full lock, windows down. A regular clicking in time with the wheels comes from the driveshaft joints; a groan when turning at a standstill points to the steering or its assistance. Neither is audible once you are on the road.

Then the brakes at a standstill: does the pedal go firm and stay there? A pedal that slowly sinks under steady pressure is a finding, not a feeling. Pull the handbrake or apply the electric parking brake on a slope and check that it holds. Select reverse and move a little — noises in reverse have causes of their own.

To close the phase, operate everything that runs on electricity, one item at a time: every window, mirrors, seat adjustment, heated seats, heated rear window, wipers on all settings, hazards, main beam, rear fog light, interior lights, all door locks by remote and by key. Those five minutes turn up more small defects than the rest of the drive.

In town the subject is the transmission of power and everything that behaves differently cold than warm. On a manual: where does the clutch bite, and can the revs be raised in a high gear under hard throttle without the speed following? That is the classic test for a slipping clutch, and it takes two seconds.

On an automatic, the first few minutes are what count. A jolt when engaging drive, a perceptible thump on upshifts, a pause before pulling away, and a change that is harsh cold and soft warm — all of these are findings, not characteristics of the model. On dual-clutch gearboxes a slight shudder when crawling in traffic is inherent; a bang on a change of load is not.

Along with that, the brakes at low speed: if the pedal pulsates, the discs are out of true. If the car pulls to one side under braking, one side is not working. And on a straight stretch put the air conditioning on its coldest setting, wait two minutes and feel the air — then the opposite, on full heat. Both have to happen quickly and unmistakably.

A road with patches, cobbles or transverse ridges is the most important stretch of the drive, because the suspension has to work there. Take it slowly, window open, and pay attention to the kind of noise rather than its volume. A metallic rattle over short ripples often comes from anti-roll bar links and is a small repair; a dull thump over a single edge points to bushes or dampers.

A creak that comes and goes with the flexing of the body is a different order of thing. It may come from a piece of trim — in which case it changes when somebody presses against it — or from the structure, and then the car belongs on a lift before anything else is discussed.

On the same stretch, check whether the car runs straight with the wheel released, where the road safely allows it. A pull to one side may be alignment, mismatched tyres or a brake caliper — in any case it is an item on your list, not a property of the road.

On an empty country road, give the engine work: accelerate hard from low revs in a high gear, two or three times. Listen for a metallic ringing under load, feel for flat spots in the pull, and watch the mirror for smoke. Blue means oil, black means an over-rich mixture, white can mean coolant — and a brief haze at cold start is normal on some engines.

On a turbocharged engine you expect boost to build, not a whistle that gets louder with load. On a diesel with a particulate filter, a regeneration may start during the drive; recognisable by a raised idle, a fan still running after shutdown, and a smell. That is not a defect — but if the seller knows nothing about it and the car has only done short trips, the filter goes on the list.

On the gearbox under load: floor it once and wait for the downshift. An automatic may change briskly and decisively but must not hunt. On a manual, drive every gear once under load, including first and reverse — a gearbox that whines in second under load will not whine on the overrun.

On a motorway or dual carriageway the subject is vibration and noises that do not exist below that speed. Classify every vibration by two things: at what speed does it occur, and where do you feel it? A shimmy in the steering wheel within a particular speed window usually comes from an imbalanced front wheel; a vibration in the seat comes from the rear. If the vibration disappears again at higher speed, that is typical of imbalance and untypical of a wheel bearing.

A wheel bearing announces itself as a steady hum that grows with speed and changes when you steer gently left or right — a soft curve shifts the load to one side, and that is precisely when it gets louder or quieter. Wind noise coming from a single direction points to a door seal or a piece of glass that has not been refitted properly.

Finally, on a clear dry stretch with nobody behind you, one hard stop from higher speed, then another. The car must stay straight, the pedal must not pulsate, and on the second stop the bite point must not be noticeably lower. If it travels downwards, that is a reason to end the drive and have the brakes inspected.

The most revealing part comes when the drive is over. Park the car, leave the engine idling and walk round it once. Put your nose near the bonnet: sweet means coolant, acrid means oil on a hot manifold, sharp means clutch or brake. Look underneath for drips, and note where they are.

Then open the bonnet — carefully, the cooling system is under pressure. At the expansion tank, the level and the colour are what matter; an oily film in it is a serious finding. At the oil filler cap, the underside matters: a light brown, foamy deposit can come from nothing but short trips, or from coolant in the oil, and the difference is the most expensive question of the day.

To finish, restart the engine warm. A starter that turns heavily when hot, and a puff of smoke on the day's second start, are findings the cold start does not show. And look at the instrument cluster once more: has a light appeared during the drive that was not there before?

Write nothing down during the drive, but everything immediately afterwards: each finding with the phase it appeared in and the condition — cold or warm, under load or on the overrun, at what speed. That attribution is what a workshop needs, and it is gone within two hours.

Two things come out of that list. First, items for the negotiation — but only those for which you can obtain a quote; how to do that is covered in the article on negotiating. Second, the brief for the workshop if you have the car inspected: a specific question about a noise you can describe leads to a diagnosis faster than a request to “have a general look over it”.