I did a few forum searches but didn't find the specific info I was looking for...<p>I drive a 2005 S40 2.4i. Because it's not a turbo, I am following Volvo's 7500 mile interval using Mobil 1 synthetic oil. If I were using conventional oil, I'd do 3750 mile intervals. <p>Anyway - I've had my oil changed twice - replaced the factory fill at 3750 with conventional oil and then 7500 using Mobil 1 5w30. I went with 5w30 because it was December and the greater Cleveland area gets VERY COLD in the winter. <p>I'm getting ready to go back for the 15k mile oil change and can't figure out if I should use 5 or 10w30. I won't go in for another oil change until spring and just want to make sure 10w30 will be ok throughout the winter. We've only had a couple of days over 86 degrees but seeing that Mobil's 10w30 pours at -45, it seems to me I can use it year round. <p>Any thoughts? Opinions? Other mid-westerners with suggestions.<p>Thanks!