does it matter or have any affect on your engine using different grades of oil when servicing. for example stealers are doing 2nd service 20k next week, but i also like to do an oil change in between services (6 month) so will it matter if i use a different grade of oil from what the dealers use. car an 08 cdti 150. also got quoted £300 for service but rang back and they quoted £240, i think that's good for a major service or am i wrong, ta all