i have a 2004 volvo xc90. in the owners manual it says to use castrol oil and that synthetics will be provided for customer at request. now then i called a volvo dealership and an oil change shop and they both told me that volvo recommends using synthetic. can i not use conventional? also the owners manual called for oil changes every 7500mi.
http://new.volvocars.com/ownersdocs/2004/2004_XC90/04xc90_09a.htm#pg129
(you have to scroll up a bit for the oil info on the link)
RepairPal Certified shops can diagnose and repair your 2004 Volvo XC90. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Synthetics are fine however not a good idea to change from one to the other depending on mileage. Synthetics will clean the enginer very well and in high mileage vehicles this can cause problems. Also the 7500 mile frequency is because the engine has a 7 quart capacity. The larger the capacity the longer it can go between changes typically.
thank you!