Although paraffinic oils are the most commonly used because of their greater stability at high temperatures, naphthenic oils are of interest in cases of low operating temperatures. These oils degrade by oxidation and form corrosive acids in the presence of metal catalysts.

They are generally limited to temperatures of 120°C for low to medium viscosities and 160°C for high viscosities.

 

However, at these temperatures, they produce a high proportion of coking residues which prohibit their use in cases where grease additives are necessary.