I've looked at the Honda UK oil recommendations for my car (2001 Prelude 2.2L VTEC) and they recommend 10W-40 to be used in this engine. Honda Canada recommends 5W-30 for the same engine. Obviously the bearing clearances are not an issue with 10W-40 otherwise Honda UK would not recommend it. Apart from a slight decrease in fuel economy and power, are there any disadvantages in running 10W-40 (Amsoil 10W-40) in this engine? Would the engine run hotter or cooler with a more viscous oil? I'd only run it in summer here in Toronto, going back to 0W-30 in winter. Also, is it OK to keep changing oil viscosities? I've heard it's best to choose one oil and stick with it.