Can anyone please explain these two things, and why they wont happen with 5W-20 and 5W-30 oils? Thank you.
Viscosity breakdown and Thermal breakdown
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Viscosity break-down is the result of the molecule chain lengths being broken. This can be caused by heat (thermal or by mechanical means (shearing), or by excessive fuel dilution. I'm not a chemist by profession but, maybe a real Chemist can explain it better. Ed
Originally Posted By: Eddie
Viscosity break-down is the result of the molecule chain lengths being broken. This can be caused by heat (thermal or by mechanical means (shearing), or by excessive fuel dilution. I'm not a chemist by profession but, maybe a real Chemist can explain it better. Ed
+1 on what they are and ANY oil can and will undergo these processes. That is why we change our oil. When it will happen depends on the application, engine, quality of the lubricant. It will happen in all cases if any oil is run long enough.
Viscosity break-down is the result of the molecule chain lengths being broken. This can be caused by heat (thermal or by mechanical means (shearing), or by excessive fuel dilution. I'm not a chemist by profession but, maybe a real Chemist can explain it better. Ed
+1 on what they are and ANY oil can and will undergo these processes. That is why we change our oil. When it will happen depends on the application, engine, quality of the lubricant. It will happen in all cases if any oil is run long enough.
Thermal breakdown is a broad term referring to the degradation of molecules as a result of (high) heat. The two most common mechanisms are "thermal degradation" and "oxidative degradation".
Thermal degradation occurs solely as a result of heat and does not require reactants, although it can be catalyzed by metals. In other words, the fluid just gets so hot that molecules begin to breakdown from the heat alone, even in the absence of oxygen. Thermal degradation for lubricant base oils usually begins well over 400°F, so it is not generally a significant factor for motor oils.
Oxidative degradation occurs as a result of molecules reacting with oxygen. It is considered a "thermal" reaction because the rate of oxidation increases rapidly with heat. In fact, the rate of oxidation doubles with each increase in temperature of just 18°F. Oxidation is a major cause of base oil breakdown, which is why all formulations contain good doses of anti-oxidant additives which react preferentially with the oxygen.
Viscosity breakdown simply means a loss of viscosity my any means. The most common means are mechanical shearing of the large polymeric molecules (VI Improvers), oxidation of the polymeric molecules, fuel dilution, and potentially thermal degradation of weaker large molecules.
Tom NJ
Thermal degradation occurs solely as a result of heat and does not require reactants, although it can be catalyzed by metals. In other words, the fluid just gets so hot that molecules begin to breakdown from the heat alone, even in the absence of oxygen. Thermal degradation for lubricant base oils usually begins well over 400°F, so it is not generally a significant factor for motor oils.
Oxidative degradation occurs as a result of molecules reacting with oxygen. It is considered a "thermal" reaction because the rate of oxidation increases rapidly with heat. In fact, the rate of oxidation doubles with each increase in temperature of just 18°F. Oxidation is a major cause of base oil breakdown, which is why all formulations contain good doses of anti-oxidant additives which react preferentially with the oxygen.
Viscosity breakdown simply means a loss of viscosity my any means. The most common means are mechanical shearing of the large polymeric molecules (VI Improvers), oxidation of the polymeric molecules, fuel dilution, and potentially thermal degradation of weaker large molecules.
Tom NJ
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