My car manual recommends 5w30 however 10w30 can be used over 20F. I had oil changed and to my dismay (probably non-issue) bulk Pennzoil 10w-30 was installed. The 5w and 10w are cold weight I believe, any other difference.
Since it's almost summer you will be fine with the 10w-30. In NH though, I'd make sure they put in 5w-30 before winter. My take is that 10w-30 will hold up better because the spread isn't as wide but then I'm not a highly technical person like some other BITOG members either.
Yes, the less the spread, the better, although this isn't as much an issue as it was in decades past. More spread typically requires more polymers to achieve same, which can burn and shear. A 10w-30 would be helpful in summer, although not required. Johnny is correct that the 5w would be appropriate for your winters, while the 10w would certainly not. Bulk oils are almost always -- if not always -- identical to bottled oils.
If it was synthetic, I would've said to just run 5w30 year round since a good 5w30 synthetic can handle the summer just as well as the 10w30. In fact I've been known to mention on here in the past that I feel 10w30 is an obsolete viscosity for synthetics, why bother when you can buy 0w30s and 5w30s which do the job just as well?
But when it comes to conventional oil, you're still better off running 10w30 in the summer over 5w30, simply because 5w30 conventional oils thin out much easier than 10w30. Plus the smaller amount of VII in a 10w30 conventional should keep your engine cleaner too.
quote: If it was synthetic, I would've said to just run 5w30 year round since a good 5w30 synthetic can handle the summer just as well as the 10w30.
Patman is knowledgeable and a good read. Other opinions exist, of course, such as the following:
Redline Oil -"10W-30 is the best choice to replace a 5w-30 or 10W-30, petroleum based or other brand synthetic oil, if maximum durability is preferred."
Not sure "maximum durability" is defined as protection over the course of a normal OCI, or rather permits extended OCI, or neither...
Some of the best oil advice I got before coming to this site was "run 5w30 in cold weather and 10w30 in warm weather". I think this is still good advice for folks who live in a region where the seasons change and whose vehicles like 30 wt.