PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 2/TASK 2
with an improperly adjusted or malfunctioning automatic choke system.
(b) A vehicle with a defective ignition system can cause oil dilution due to
misfiring spark plugs. Whenever a spark plug misfires, most of the unburned fuel
will be forced into the exhaust system but a small portion of it will also pass the
(c) An engine with a malfunctioning thermostat, or an engine that is operated
for short durations only, will never reach a sufficient temperature to burn the
fuel completely. A small amount of oil dilution occurs in all engines from initial
startup through warmup. When, however, the engine reaches its operational range
(180 F (82.2 C] to 200 F [93.3 C]), this condition is corrected as the excess
gasoline vaporizes in the crankcase and is carried off by the crankcase ventilation
American Petroleum Institute (API) Rating System.
(1) General. The API system for rating oil classifies oil according to its
performance characteristics. The higher rated oils contain additives that provide
maximum protection against rust, corrosion, wear, oil oxidation, and thickening at
high temperatures. There are currently six oil classifications for gasoline
engines (SA, SB, SC, SD, SE, and SF) and four classifications for diesel engines
(CA, CB, CC, and CD). The higher the alpha designation, the higher is the quality
of the oil.
(2) API Designations.
light loads, moderate speeds, and clean conditions. SArated oils generally
contain no additives.
(b) SB (Minimum Duty Gas Automotive). Adequate for automotive use under
favorable conditions (light loads, low speeds, and moderate temperatures) with
relatively short oil change intervals. SBrated oils generally offer minimal
protection to the engine against bearing scuffing, corrosion, and oil oxidation.