Hi folks, Picked up a 2004 Sienna. I've driven it 4k miles. Hardly any oil loss and the oil is still clean. Doing a first to me OC. I've read that Toyota has back spec'd this vehicle to 0W20, 0W25. Oil cap says 5W30. Is it worth trying to get a little better fuel mileage by going to the lighter weight? Any advice greatly appreciated. Already baught a jug of Mobil 1 high mileage full synthetic 0W20. Guess I should of asked first, but I'm thinking I'll do fine with it. Thanks in advance...