ive used 10w.40 for nearly 3 yrs of owning the car and works great,gets regular changes as well.i did however use the millers 5w.30 and it didnt go down very well.we dont rag the car me and the missus use just to get around to work do the shopping and for the kids and ocasionly go out places.but 10w.40 has never give us problems.i think its how the car has been treated to be honest