Under the hood

The Engine

A dirty engine points to vehicle neglect. On the other hand, a sparkling clean engine means it has recently been steam-cleaned, quite possibly to hide defects.

Have a good look for any frayed or burnt wiring, oil streaks and poorly attached or damaged hoses. Look especially carefully around the carburettor and fuel lines for petrol leaks.

Check the oil. Black, soupy oil may indicate poor engine maintenance. Look under the vehicle for any oil leaks or other drips. Oil leaks eventually mean expensive repairs.

With the engine running, lift off the oil filler cap. If large amounts of gas come out (and especially if the gas has a blue, smoky tinge) then this is an indication that the engine is badly worn.
As a second check, idle the engine for a few minutes then get your friend to watch the exhaust pipe while the engine is revved.

A single puff of blue smoke from the exhaust during the revving means the engine is worn, although not badly. However, continuous blue smoke coming from the exhaust means the engine is badly worn.
(This test is not valid for diesel cars, but the test of gases coming out of the oil filler cap is).

The Radiator