You're looking for any and signs of mechanical neglect by former owners which you could end up paying for. If under the bonnet is an unfamiliar place to the seller they probably haven't done any basic servicing like checking the oil, water and brake fluid levels.

Try to make all engine checks with the engine cold, it's more revealing of the engines's condition, be wary if it has been warmed up time you get there, a warmer engine is quieter and less smokey, if it has been warmed up be suspicious, there may a number of major engine and gearbox problems.

Check that the engine is clean, if the engine is extensively oil covered you could be looking at an engine that has always run with too little oil in it, an engine that will have much greater mechanical wear than it's age and mileage might indicate.

Check the radiator for leaks. Open the radiator cap and look for any sign of an oil film on the the water - usually a sign of a defective head gasket - check also the colour of the liquid inside the radiator, it shouldn't be brown, rusty, smelly, water. It should be green showing the presence of anti-freeze, sign of being looked after. Generally the stronger the green the better the anti-freeze content.

While around the radiator it's worth checking the condition of the hoses and their clips and any fan or drive belts nearby. 

Under the bonnet check that the engine is reasonably clean  with no obvious oil leaks. Does it idle comfortably at  under 1, 000 rpm ? Is the exhaust emission fairly clean as an excessively sooty or oily exhaust can mean major problems later. Are there any unusual noises when you rev  it up ?

Open the oil filler neck is there a mayonnaise type substance inside that means water

Check the oil both with the dipstick and by undoing the oil filler cap. If the oil is  thick and grey it's old and tired not having been changed for long time, if there's any sign of water in the oil the head gasket is probably defective allowing oil and water to mix, repairs would be expensive.

If there's a thick, creamy, material - known in the trade as mayonnaise - on the underside of the oil filler cap this is a clear sign there has been water in the oil for some considerable time. Fresh oil should be black and free running.

With a turbo car check carefully the colour of the engine oil, if it's been overheated - a common problem - the turbo may be damaged which can cost hundreds of pounds to put right.

Look at the rear panels and boot lid and under the rear bumper, lots of soot means a smokey, oil burning, engine with big troubles.

Run a finger into the end of the exhaust pipe, if the deposits are black the car is running too rich or burning oil, if light brown it's probably running too lean and needs some adjustment, mid grey/brown is about right. 

A smoky diesel - grey or black smoke - is always bad news implying high and hard mileage perhaps with little regular servicing, as a minimum the injection system clearly wants setting up properly, not cheap.

Check if the cam belt has been replaced in the last 30, 000 miles, if not it could break which can destroy an engine, very expensive. Get at least £100 for a replacement knocked off as a contribution. 

If the car has an automatic gearbox find the filler and check the fluid for colour, it should be thin, clear and pink, if it's rather muddy and grey it hasn't been replaced for a long time. Beware, a new autobox can cost a £1000.

If it won't start at all do not buy, if it starts but sluggishly allow about £40 for a new battery.

As the engine starts check there is not excessive smoke or a lot of odd noises.
A bit of blue smoke on start is not uncommon with older cars but if it doesn't ease after a few seconds and if it reappears when you push the accelerator pedal down several times then there are some expensive things going wrong in the engine and you don't want that expense.

Listen carefully to the engine noises as it starts, a light clattering at the top of the engine usually means the valve gear needs some adjustment, not enormously  expensive, perhaps allow £100. A deep rumbling noise at the bottom of the engine suggests the bearings may be worn, a very expensive problem that you really don't want. Walk away.

Once started listen to the exhaust note, if it sounds rough it very probably is, either there are engine problems or the exhaust or silencer are split or holed.

Look at the dash, if the oil light stays on it could be big trouble, walk away.

If you find anything wrong try to get the vendor to knock a suitable amount off the asking price, if they won't budge walk away.


Abstracted from the book “Buying a Used Car” © G Benge 1997-2007

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