A method to use a heat transfer oil, comprising: a. selecting a heat transfer oil having an auto ignition temperature greater than 329° C. (625° F.) and a viscosity index greater than 28×Ln(Kinematic Viscosity at 100° C., in cSt)+80; wherein the heat transfer oil comprises a base oil, made from a waxy feed, with the base oil having: i. greater than 10 weight percent and less than 70 weight percent total molecules with cycloparaffinic functionality, wherein the one or more fractions have at least 31.2 wt % 1-unsaturations by FIMS; b. providing the heat transfer oil to a mechanical system; and c. transferring heat in the mechanical system from a heat source to a heat sink.