What is the temperature range you experience when running your generators and pumps? It can get down to zero or lower and up to 100 on rare occasions where I live but my generator is stored in an attached garage. The oil will probably never below 25 F at startup. Somehow I doubt that the 5w of the 5w-40 RT6 I've been using is really necessary, and yet I remain hesitant to move up to 15w-40 RT6.I use 15W-50 which does wonderfully in my Subaru powered 5500W generator, Kawasaki water pump and other hard working engines. The pressure washer and lawn mowers and tractors generally get Rotella T6 5W-40.