I have a 04 525i with 122k on the engine currently, I have owned the car around 4-5 months now, prior to owning it I am unsure what oil was used in car, but when I did my first oil change in the car I used Valvoline full synthetic high mileage 05 w30, I like the way it feels in the car but if I'm right I believe I am getting worse gas mileage than when I got the car and one thing I know for sure is since doing the change I have developed a leak somewhere around the oil filter housing, most likely the housing itself which I am not sure is something that is caused by maybe not fighting the cap to the right torque, maybe the oil is thinner than what was privioiosly used causing it, or if the o-ring that cane with the new filter was bad and that's what is causing it. Another thing I have noticed since doing the change is that somewhere from the bottom of the engine, possibly the drain Pan I am leaking something as well, however this leak only happens when the car is running and it is a slight drip, it almost leaves behind the same thing condensation does when parking running the ac just a lil smaller of a puddle an I am almost positive its oil being left behind, I used a pump running thru the dipstick tube when I did my oil change so im thinking maybe I need to change the drain plug as well as seal there too? One final thing is somehow one qt of the oil I bought was conventional, the same brand and viscosity just not synthetic and it was added to the car awhile back when I noticed I was low on oil after a drive, since I haven't driven it much because I want to make sure 1 that this isn't going to mess the engine up at all and 2 if you guys think I should change the oil again soon an maybe go with 10w30 or 5w40 to see if that helps with any of the leakage im having?
