Mirage with 158,000 miles which weight?

[UncleS2]

Might try a 10w30 for the colder months, & if that works OK, stick with it year-round. If you want something a bit "stiffer" for summer, try a good 15w40.

 

[MustangGT]

I've got a 1989 Mirage with 158,000 miles. I've been using 10W-40 the last year or so with no problems, I've noticed that some people here have discouraged the use of 10W-40. My manual says I can use 10W-30 too, is it a good idea to switch? What really is the difference between the two oils? During the summer my maunal says I can use 20W-50 if it is above 32F outside (summer), is it a good idea for extra protection at higher temps?

Thanks