Oil viscosity represents a measurement of how well oil flows. When oil flows smoothly, its viscosity is said to be high. When it clumps up or moves slowly, the opposite is true. The temperature of an engine and that of the outside environment have a significant effect on the viscosity level of engine oil. The minerals present in the oil and its refinement level determine its viscosity, as well -- up to certain prescribed temperature limits.
Engine oil flows best -- it has optimal viscosity -- within temperature ranges of zero and 200 degrees Fahrenheit. For this reason, oil brand products are rated with regards to how well they perform within these temperature limits. Beyond these parameters, many oils begin to either clump up in the cold or burn up from heat. The effect at either end of the temperature spectrum is a loss of lubrication in the engine. This, in turn, creates friction and heat, which ultimately damage and ruin exposed engine parts.
Extreme Cold Effects
Depending on the engine oil's formulation, each product has a "pour" point: This limitation is the lowest temperature point at which the oil will still flow before it starts to coagulate into a gel. Normal engine oil may not do well much beyond freezing (32 degrees Fahrenheit). However, specially formulated oils can retain viscosity at temperatures as low as -5 degrees Fahrenheit, during prolonged use.
Extreme Heat Effects
When engine oil reaches the upper limits of its heat toleration, it may seem extremely viscous, but in reality the oil minerals are beginning to break down. This chemical deconstruction ultimately results in a boiling or burning up of the oil. The liquid will carbonize and turn into a tar-like substance as it breaks down completely. Again, the engine loses lubricant in the process, and too much oil loss will expose parts to friction, heat, and ultimately damage.
Types of Oil and Environment
When driving in a cold environment, more viscous oil will benefit the engine, as the liquid can still flow smoothly through cold lubrication systems. Particularly regarding the starting of the engine, a thin-flowing oil can protect cold parts that would otherwise grind badly in cold temperatures. Lower viscosity oils protect parts under hotter temperatures by still retaining chemical integrity at heat points where thinner oils would just burn up. Parts continue to move freely instead of getting gunked-up with tar and carbon flakes. Many race car teams use specially-formulated oils with very thick consistency to protect performance engines running at very high speeds and transmission demands.
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