The engine is the heart of the vehicle and should be scrutinized. Before you start the vehicle, take a look at the overall condition of the engine area. Is it clean or oil filled, dirty, and clearly neglected? Many owners bring their dirty engine compartment to the car wash to be power washed with a high pressure hose using degreasing fluid or hot water. If the engine is the only clean part of the vehicle, this is probably the case and calls for extra attention to what you cannot see. The internal parts of an engine depend on oil to live. Check the oil first. If the oil is clean- tan or brown, but not black, ask when the last oil change was completed. Look on the windshield for your local quick-lube's oil sticker and if present, check the date against the mileage on the car. If the oil was changed that morning or recently, remember to check the oil again after your test drive. If it is black after the drive, there is serious wear and the price should reflect that.

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. 

Sounds:

One final check of the engine would be to let it run and reach operating temp. When engine is good and hot race engine slightly and listen for any noises like a rod bearing knock or a weak hydraulic lifter tick. Knocking or ticking sounds that increase with engine speed usually represent significant problems and costly repairs. If you are not able to assess these sounds yourself, call a vehicle inspection service, should you still be interested in the vehicle. Do not buy on impulse because the car is the color you like, while the engine is blowing smoke or knocking. There is always another car out there, so let some other sucker buy this one.