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How Temperature Impacts Oil Condition

“If an oil with a viscosity grade (ISO VG) of 680 has an oil temperature of 60 degrees C but the journal bearing temperature is 88 degrees C, will it affect the oil condition or can the oil withstand this temperature?”




  1. Temperature affects many things in the realm of machinery reliability.
  2. At this elevated temperature, you would expect :
    • The viscosity decrease, the lubricant film become thinner,
    • An acceleration in abrasion and scuffing conditions,
    • The oil to age sooner,
    • The additives deplete quicker,
    • An acceleration of corrosion
    • The formation of sludge and varnish.
  3. A few of the side effects of running at a higher temperature, but play a critical role in the overall health of the machine and the lubricant.
  4. The relationship between temperature and chemical reaction rates (oxidation or the chemical aging of the oil) was theorized by Svante Arrhenius around the turn of the 19th
  5. Lubricants will degrade twice as fast for every 10 degrees Celsius the temperature is increased after their base activation temperature has been reached.
  6. Viscosity is the single most important property of a lubricant, and everyone knows that a change in temperature leads to a change in viscosity.
  7. This temperature difference accounts for a drop in viscosity of 71 percent, assuming the lubricant in question is a mineral-based fluid with a viscosity index of 95.
  8. This drop-in viscosity has a staggering effect on the film strength and the ability of the lubricant to keep the journal bearing from operating in a boundary (metal-on-metal) condition.
  9. The selection and use of an ISO VG 680 oil in a journal bearing is outside the ordinary. This specific application would have to be very slow-moving and/or very heavily loaded to warrant the use of such a high viscosity.
  10. The ISO VG 680 oil provides 59.38 cSt.
  11. This is extremely excessive, and the consequences can result in heat generation and energy consumption because of internal fluid friction.
  12. Elevating the temperature to 88 degrees C will affect the oil condition, but the root cause of the heat may be an incorrect lubricant selection.
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