By changing to API?Group II base oils, gas turbine fluid formulators have improved their products oxidative and thermal stability. With that switch, however, came reduced solubility and the costly side effect of increased varnish formation.
The importance of careful fluid selection cannot be overstated. There are no indications that original equipment manufacturers plan to revert back to Group I oils; in fact, as time progresses, the likelihood of moving to even more refined oils, such as Group III and Group IV, increases. Likewise, the demands placed on turbines and the operating conditions required to meet them are here to stay.