I use it for both of my daily drivers, an 06 Corolla and 05 Dodge 3500 Cummins, its hard to say if it makes a quantifiable difference in MPG or smoothness and idle quality. The Corolla likes Redline in the transmission, very smooth definitly a winner, I use 5w30 in the engine and the only difference I see is zero oil use between changes even at sustained high rpm trips. The Dodge has run Redline 15w40 for about 25000kms and I just sent a oil sample away with 14000kms on the oil, I think the benefit is more long term rather than sensory, by that I mean its hard to tell a big difference driving it around but I believe there is a small bonus that adds up over time. When I've got 500000kms I bet the difference would be easier to tell. We're subjected to -40C in the winter and Diesels have more power and run hotter than ever before so I feel the Redline is warranted in my application. Need to switch to 5w40 this winter! To be realistic though I am hopelessly biased, I love Redline oils so I'd use them for anything and they're an American company, whats not to like!