Visual Checks:

Make sure the motor oil is at full level. This will tell you if the motor is leaking or burning oil. Even if the oil level is full, the motor can still have an oil consumption problem. Look under the front of the car for oil leaks. Common sources of leaking oil are valve covers, oil pan, and front and rear engine seals. Any oil visible on the sides of the engine is a good indication of these problems. One way to check the inside of the engine for sludge build up is to remove the oil fill cap and inspect it. Also look inside the valve cover for sludge and oil build up. This inspection will indicate how often the oil was changed and if the engine was neglected. A well-maintained engine, regardless of mileage, will be fairly clean inside.

Ideally, you want to start the motor cold to assess for difficulty starting, and blue smoke, which indicates oil being burned or sucked into the cylinders- perhaps through worn valves. Let motor run for awhile at idle, then race the motor slightly and check tailpipe for smoke, thus indicating a oil burning problem. Engines with these problems should be avoided unless you want a headache.