We probably will go to the 10-30 Mobil 1 Extended performance. Our Engine rebuilder recommended the lower viscosity to get oil to the Bearings more quickly on start up. We did get 5 years on this engine(same as Marty on His engine) We used to Change every other Race weekend but then when we started running the Pro-it weekends with 30 minute practice and 45 Minute race. Plus we try to run regional if on same weekend we went to changing every weekend. Always some oil remains in cooler and lines. use the Idemitsu for our premix. Need to find an East coast source for Idemitsu to cut coast of shipping . Our Engine on tear down showed wear but not certain that may have been there when we got the car.