Every engine needs oil between its moving parts not only to reduce friction but also to carry away heat. Oil is the primary means by which the rod and main bearings are cooled, as well as the pistons. So any reduction in oil flow may cause these parts to run hot, gall and seize.

Low oil pressure is often a contributing factor in engine failures. The underlying cause may be a worn oil pump and/or excessive clearances in the main and rod bearings as a result of high mileage wear or neglect (not changing the oil and filter often enough).

Oil starvation is almost always fatal to any engine, and is usually the result of a failed oil pump, a plugged oil pickup screen inside the oil pan, or a low oil level. Bearings that have been damaged as a result of insufficient lubrication will be shiny and worn where the crankshaft journal wiped away the bearing material.

Overhead cam(OHC) engines are even more vulnerable to oil starvation and low oil pressure problems than push-rod engines because the cam and valve train are farther from the pump.
When an OHC engine is first started, it takes a while for oil pressure to reach the cam bearings. If the oil viscosity is too heavy (especially during cold weather), it may delay the arrival of oil long enough to starve and seize the cam. For this reason, most vehicle manufacturers recommend using a 5W-30 oil inlate model OHC engines year round, but especially during cold weather. Refilling the crankcase with the recommended viscosity oil can prevent a recurrence of this type of failure.

If you suspect engine damage may have been caused by a low oil level, check the dipstick to see how much oil is in the pan. A low oil level may be the result of neglect, oil leakage and/or oil burning.

Oil-fouled spark plugs and a heavy buildup of black wet deposits on the backs of the intake valves and in the combustion chambers would tell you the engine had been using oil. Oil usually enters the combustion chamber past worn valve guides and seals, and also past worn or broken piston rings and worn cylinders. Worn valve guides can sometimes be knurled to reduce clearances, but usually it requires installing new guides, guide liners or valves with over sized stems.

Installing new valve guide seals can often reduce oil burning dramatically. An engine that sucks a quart of oil every few hundred miles may be able to go several thousand miles without using any oil with a new set of valve guide seals.

Any evidence of oil leakage around the front or rear crankshaft seal, pan gasket, valve cover gasket or other gaskets, would tell you new gaskets and seals are needed. Most of these gaskets and seals will have to be replaced anyway if you are opening up the engine.

Bearings ruined by dirty oil will have foreign material embedded in the surface and/or be scored by debris. Check for a plugged oil filter and/or a missing air filter or oil filler or breather cap. The underlying cause here may be not changing the oil often enough.

Culled from Automedics

Motoringnigeria..com