N ORDER TO START effectively, engines must reach a critical cranking speed. As temperatures drop, achieving critical cranking speed becomes more of a challenge. Low temperatures cause motor oils to thicken, and if they thicken too much and impose excessive drag on moving parts, critical cranking speed will not be reached and the engine will fail to start.
Motor oils used in winter climates must maintain a sufficient low cranking viscosity to allow engine turnover at the lowest temperatures. If a motor oil is able to meet the challenge of allowing the engine to turn over, it immediately faces another critical challenge: providing quick, critical lubrication to the engine's bearings and other moving parts.
Two types of engine pumping failures can result from cold-thickened motor oil: air- binding failure, and flow-limited failure. Air-binding-failure occurs when the thickened motor oil surrounding the pump inlet screen gets sucked into the pump, but is not replaced by new oil from the sump. The oil pump inlet screen then becomes starved for fluid, and oil pressure becomes erratic as air is entrained and proper oil flow cannot be maintained. Flow-limited failure occurs when the motor oil becomes so thick that it cannot be pumped through the inlet tube and through the narrow passages that deliver oil to the engine's moving parts.
All motor oils thicken in cold temperatures, but how much they thicken is significant to the level of protection an engine receives. Pour point tests (ASTM D-97) pinpoint the temperature at which a motor oil thickens to the point where it ceases to flow. Of course, when oil stops flowing altogether, it is useless. For an engine to receive even minimal protection from an oil, it is important that it has a pour point lower than typical winter temperatures.
Conventional motor oils face significant challenges in low temperatures because they contain paraffinic (wax) materials. As temperatures drop, the wax components crystallize and agglomerate into large structures. Eventually, the motor oil jels, and becomes resistant to flow and fails to provide the engine with the lubrication it needs. In order to hinder the development of these wax crystals, conventional motor oils are additized with polymers known as pour point depressants. These pour point depressants prevent wax crystals from agglomerating and can lower the oil's pour point. In fact, petroleum motor oil without additives typically has a pour point of only around 5°F, but the inclusion of pour point depressants can lower the pour point approximately 25°F.
Synthetic motor oils do not contain the paraffinic materials present in conventional motor oils, so they do not require pour point additives. Synthetic motor oils naturally flow at much lower temperatures than conventional motor oils, maintaining their cold- temperature protection properties over a longer period of time.
Cold weather operation also increases problems associated with condensation. The colder the weather, the longer it takes for the engine to warm to the point where condensation evaporates. During short trips, the engine may not have a chance to evaporate the condensation at all. Eventually, condensation causes acids to form in the oil, causing corrosion.
Rust and corrosion inhibitors serve to neutralize and protect engines against water and acids. These oil-soluble additives have a greater affinity for metal than for water, thereby forming a protective film on engine parts. The Total Base Number (TBN) of a motor oil is an indication of how well it combats acids. The higher the TBN number, the greater the degree of protection.
AMSOIL Motor Oils are formulated with high TBN. In fact, AMSOIL 5W-30, 10W-30 and 0W-30 Motor Oils all have TBN's over 11, allowing them to effectively fight acid and corrosion for extended drain intervals.
AMSOIL Synthetic Motor Oils remain fluid in the coldest operating conditions. Maintaining their fluidity and protecting ability in temperatures as frigid as -60°F, AMSOIL not only permits easy engine cranking for quick starts, but flows to crirical engine components in a quarter of the time that conventional oils take. Considering that up to 60 percent of all engine wear occurs during cold starts, this immediate lubrication is essential to long-term engine wear.
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