Nobody is going to become expert in detecting mechanical faults just by reading a book or ‘How To’ article. What we can do here is provide readers with sufficient clues to identify an engine that’s soon going to need major work, therefore avoiding the cost of sending that vehicle for professional inspection.

Don’t assume just because an engine doesn’t rattle or blow plumes of smoke that everything internally is sound or a costly failure isn’t imminent.

However there are obvious checks a buyer can perform that involve looking, feeling, listening and smelling.

Before your test drive and with the engine cold – see ‘Test Driving’ – remove the radiator or overflow tank cap to check the colour and cleanliness of the coolant. Many engines built during the past 25 years have alloy cylinder heads which require anti-corrosive coolant, not plain water. Corrosion-inhibiting coolant can come in a variety of colours but they certainly don’t include rusty brown.

Engine oil should be at the correct levels – take your own rag to wipe the dipstick before checking the level. Dirty oil indicates neglected maintenance. If there’s a gooey or milky residue inside the oil filler cap or showing on the dipstick it’s a fair bet that the cylinder head has cracked or a head gasket is leaking.

Overhead-camshaft engines have their own sets of problems, including wear to the camshaft lobes that will cause ‘chattering’ or clicking sounds. The timing belt or chain that keeps the shaft turning in unison with the pistons is a vital component and must be changed or adjusted regularly. If a chain is loose or a belt slips or breaks, valves can hit the pistons and cause extensive damage.

If the vehicle doesn’t come with a receipt confirming replacement of the cam-belt within the past 60,000 kilometres or three years, budget for immediate belt replacement when negotiating the purchase price.

Rumbling or knocking from inside the engine can indicate crankshaft, bearing or piston wear – all expensive to repair and deal-breakers when buying a low-value car unless you can rebuild the engine yourself and purchase the vehicle very cheaply.

Don’t forget to inspect the exhaust system as far as is possible for leaks or damage. Petrol-engined cars and commercial vehicles built since 1986 have catalytic converter that are meant to minimize exhaust emissions. Most of those original ‘cats’ are now very dead; their condition affecting engine performance and likely to fail emission tests that may be conducted as part of some State roadworthy inspections.

Cars built during the past 20 years will usually be equipped with fuel-injection – reliable and economical when well-maintained but thirsty and expensive if neglected. Engines that are difficult to start when hot, blow black exhaust smoke and stutter under acceleration will often be suffering a fuel system malady.

Some problems can be cheaply rectified, others involve replacement of electronic sensors or the injectors themselves and all of that can be very costly.

Turbochargers that are fitted to some cars and a lot of diesel-fuelled 4WD and commercial vehicles need special attention. Heat generated as exhaust gas passes through the turbocharger affects nearby components, so look for burned or missing insulation or taped-over wiring. Failing turbochargers emit white smoke due to oil or coolant getting past internal seals.

Overheating is a common problem with older cars. Frequently, the remedy is a radiator flush, new coolant and maybe a water pump but that won’t cure damage that has already been done to engine components. Look at hoses for leaks and cracks and stains around the water pump. Rust marks or leaks from the radiator core – the finned section below the top tank – provide further evidence that repairs were neglected.

Engines have rubber mountings that can soften with age or break. You can often see the front mountings by looking down beside the engine. Use a small torch for extra illumination. Thumping from the cabin floor, ticking noises that indicate the fan blades are hitting their shroud or marks from fan blades hitting the radiator point to worn or broken mounts.


Checking the fluid level in an automatic transmission can be difficult. Most need to be dipped when warm and with the engine running to give an accurate reading. Still check the oil on the dipstick which should be red, not dirty brown or black and be concerned if it smells burned or has a gritty feel.

The oil level in a manual gearbox is even harder to see, but excessive heat and gear selection problems can be a giveaway. If the car has a floor-shift, feel the metal shaft of the lever after your test-drive. If it’s hot after just a few kilometres and gears become harder to engage, the gearbox is likely short on lubricant.

Visually inspecting a manual or automatic transmission for leaks will be difficult unless the vehicle is on a hoist. If rubber or vinyl boot around the gear-lever is torn or loose, this must be repaired so fumes don’t enter the cabin.

Down-changing when a manual gearbox is cold can reveal worn synchromesh which makes selecting the desired gear difficult. Shifting quickly from third to second gear is a good test, as is selecting reverse immediately after the vehicle has stopped.

If an automatic transmission takes more than two seconds to engage, it has potentially expensive problems. If there is a noticeable shudder when accelerating this can be due to contaminated fluid or worn clutch units. Both can be expensive to fix. Knocking sounds can be due to loose bolts where the transmission’s driven plate mates to the engine. Not difficult for a technician to check as autos have inspection covers, however if there is a problem the transmission must come out.