I got this from my 93 Manual. It was a response I made to someone who asked the same question a couple of months ago, so I just copied and pasted:
>32 F: 20W-40 or 20W-50 is OK
>-10 F: 10W-30, -40, or -50 is OK
<100 F: 5W-30 or -40 is OK
>32 F: 20W-40 is OK
>-10 F: 10W-30 is OK
<60 F: 5W-30
So to answer your specific question, if you have a non-turbo, you probably don't have to switch between 5W-30 and 10W-30 at all unless you just want to. Both are OK as long as the temperature where you live usually stays below 100F in the summer (if not, use the heavier oil at least in the summer). If it usually goes below -10 in the winter, use the lighter 5W-30 oil. Otherwise, you can use either one.
If you have a turbo, it looks like you don't want to use 5W-30 at all (most places go above 60F even in the winter on occasion), but just stick with 10W-30 unless you are in a very mild climate that doesn't go below freezing; if you are, use the 20W-40.
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