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Hot and Cold Temperature Extremes Call for Superior Motor Oils 

Hot Temperatures

A significant challenge faced by today’s motor oils is maintaining an adequate level of protection during high temperature conditions. Without a quality motor oil protecting it, an engine can be damaged through motor oil breakdown, viscosity increase and deposits – all caused by excessive heat. 

All motor oils are subject to vaporization when exposed to high heat. How much an oil vaporizes is measured by the NOACK Volatility Test (ASTM D-5800). Conventional motor oils tend to vaporize the most, the lightest fractions evaporating first and leaving behind a thicker, harder-to-pump motor oil. The uniformly sized molecules of synthetic motor oils are much more resistant to vaporization. Less oil evaporates and viscosity remains consistent. 

The flash point of a motor oil is the lowest temperature at which application of a flame will cause lubricant vapors to ignite. Higher quality base stocks exhibit higher flash points, and the higher a motor oil’s flash point, the better the protection. 

AMSOIL motor oils are formulated with high flash points, keeping volatization to an absolute minimum and maintaining their superior protective and performance qualities in extreme heat conditions. In fact, a look at the chart shows AMSOIL 5W-30 Synthetic Motor Oil loses significantly less of its original weight during high-temperature service when compared with competing motor oils.

As motor oils operate in high heat, especially over extended periods, they tend to thin out and lose their ability to provide adequate wear protection. Viscosity Index (VI) indicates the degree of an oil’s viscosity change over a given temperature range (between 40°C and 100°C). The higher a motor oil’s VI number, the better it is able to maintain its viscosity over a broad temperature range, translating into better wear protection in both hot and cold temperatures. Motor oils with low VI do a poor job of maintaining viscosity in temperature extremes. They are very viscous (thick) at low temperatures, while very thin at high temperatures.

Motor oils formulated with synthetic base stocks usually have naturally high VI numbers, giving them the ability to resist viscosity change in high-temperature operation. Conventional motor oils, on the other hand, require high amounts of viscosity index improvers that increase the relative viscosity of motor oils during high temperature operation. Viscosity index improvers can be thought of as springs, coiling at cold temperatures and uncoiling in high temperatures. Uncoiling makes the molecules larger, increasing internal resistance within the thinning oil and reducing the overall viscosity loss of the fluid.  

Viscosity Index Numbers  

AMSOIL Synthetic Motor Oils have “ultra high” viscosity indices, allowing them to stay in grade and provide superior wear protection throughout extended drain intervals. In fact, AMSOIL 10W-30 Motor Oil was recently subjected to a triple length Sequence IIIF test. Even after being subjected to the test three times longer than the standard length, AMSOIL 10W-30 performed three times better than the standard test limits. The competitor’s motor oil showed dramatic viscosity increase in less than half the time.  

Oil heated in the presence of air oxidizes, forming damaging acids and deposits. The higher the temperature, the higher the rate of oxidation. Oxidation inhibitors are added to motor oils to minimize the high temperature deterioration process, while detergents and dispersants minimize the formation of sludge and deposits, neutralize acids and hold solid contaminants in suspension. AMSOIL Synthetic Motor Oils are formulated with the highest quality additive packages, resisting the damaging effects of heat and oxidation much longer than conventional motor oils and keeping engines running clean and deposit-free.  

Cold Temperatures

In 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 achieved 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 significant 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 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 the 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 wear protection from an oil, it is important 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 gels, 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 by approximately 25°. 

Synthetic motor oils do not contain the paraffinic material present in conventional motor oils, so they do not require pour point additives. Synthetic motor oils naturally flow at much lower temperatures than conventional  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 water, 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 critical 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 life.