SEVERE DUTY ENGINE CONDITIONS AS RELATED TO OIL AND FUEL 400088
Engine performance (availability and operating costs), maintenance (parts affected) and life (general overhaul period) are today a problem of severe duty engine conditions. Severe conditions, generally, are measured in terms of high power output (horsepower per cubic inch of piston displacement or BMEP). Such operations have brought about high piston ring groove and valve guide temperatures, which greatly increase ring and valve sticking tendencies.
In the case of some passenger car engines at high speed and some truck and bus engines overloaded, ring sticking is not a problem but high crankcase oil temperatures cause excessive oxidation resulting in varnish on piston skirts and overhead valve mechanism. Time between crankcase drains, alloy type bearings and blowby contamination all relate to the severity of engine conditions.
Severe duty engine conditions have brought forth an intensive study of the oil and fuel problem as affected by high piston ring groove and valve guide temperatures and high crankcase or oil circulating temperatures. It is the desire to develop better oils so that the performance of high output engines can be increased to the limits set by the lubricants yet limit the types of oil necessary to a minimum. It is particularly difficult to evaluate the stability of motor oils since the aging condition prevailing in the engine is subject to constant change and differs from one engine to another.