Ok I got an oil change and the shop put in 10-40w. If im correct this is a high mileage oil for older engines? the manuel on my rav recommends 5-30w to 10-30w so why would the shop use 10-40w? He told me it would help my rav run better but so far it just feels like its got sludge in the engine and is having problems getting into gear and switching between them like there is to much oil in the car. I checked the dip stick and it looks fine. So is the 10-40w hurting my car? or am I just parranoyed.