Sorry if this question seems very basic. I'm intermediately knowledgable mechanically speaking, but I'm not positive on this one. I just took my car in to get full serviced (I can do it...but it's worth the $ for the aggrevation)(oil filter), and they put 5/20 oil in it. They also told me the sticker said in the last oil change they'd put 10/30 in it and that was incorrect. The 5/20 didn't sound right to me, so I went online and ford is recommending 5/30 for the Mark VIII, so my question is...do I need to go back there tomorrow and make them put 5/30 in it? What do you all put in yours, and how harmful could this be? I've asked a few people, and they either didn't know, or said there wasn't much of a difference between 5/20 and 5/30. So the answer seemed to be to track down some Mark VIII experts. Thanks.

mobil 1 5/w30 for the north, and 10/w30 for the south. both synthetic i use 5/w30 here in fl

You be fine w/ 5W-20, esp. this time of year in CO. I know a lot of mod motors are running 5W-20. I'd worry more about the 10W-30. Now ask what brand oil and filter. :W

Thanks very much for your input. So what brand oil and filter would you guys recommend? On a random side note, I had them replace the air filter. What our your opinions on doing cold air? I haven't, because I figured to really get any upgrade I'd have to do headers and exhaust too...which are both whole other extensive forum topics on their own.