The main factor that limits the use of mineral oils in high temperature applications is their oxidation stability, rather than the viscosity thinning or thermal stability. In the presence of air, it is generally not advisable to use mineral oils in any application at temperatures above 200 degrees F (93 degrees C).

From "The Practical Handbook of Machinery Lubrication"

Rules for Dealing With Aftermarket Additives and Supplemental Oil Conditioners

RULE #3: Increasing the percentage of a certain additive may improve one property of an oil while at the same time degrade another. Example (a) Some additives compete with each other for the same space on a wear surface. If a high concentration of a special anti-wear agent is suddenly added to the oil, the corrosion inhibitor may become ineffective. The result may only be an increase in corrosion related problems.

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Question: What temperature and viscosity units do ISO Viscosity Grades relate to? Please use the correct units for the ISO standards.

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Sludge and varnish can occur in even the most well-maintained machines. In this article learn how sludge and varnish form and analysis techniques for monitoring them.
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