I bought my XC90 used and the previous owner used Mobil1 10W30 so for the time being I did the same. Since Volvo recommends 5W30 and also recommends only topping up with whatever oil is currently in your car, is it safe to simply switch to 5W30 when I change my oil next? I'm assuming it's ok, but just making sure. Thanks.

 

Yes its fine to switch back to dino oil. In fact service manual states not to use synthetic if you change oil at recommended intervals.

also, if you have an Advanced Auto Parts store nearby, Castrol Oil with Oil Filter is on sale for 14.99 (5 qts)