Should I use 5w30 or 10w30 in a 99 LHS?

I recently purchased my 1999 Chrysler LHS in great condition, with 70,000 miles on it.

The mileage just turned 75,000 miles and I brought the car to Valvoline to have the oil changed. I just realized that they put in 5w30 instead of 10w30. The manual is clear in showing 5w30 from below 0 degrees F to 38 F. And 10w30 from 20 F to over 100 F. I live in the Pacific Northwest, summer is about 80 to 100 degrees while winter is about 30 to 40 F.

Normally I would just use 10w30 year round, but this got me doing some research & I've found that a lot of people recommend the 5w30 year round.

Does anybody here have any recommendations or strong opinions any other way for 5w v. 10w 30?

Also while we are talking about this, what are your thoughts on synthetic oil for this engine?

Thank you, it is appreciated!

 

What engine size?

 

It has the 3.5 V6.

 

10w 30 if u start using synthetic u will need to keep using u cant go back to normal oil so be prepared for that

 

10W30 Year round, 5000 OCI, save your money and use regular oil.
FWIW Timing belt on the 3.5 neds to be done 7 yr/105k and you are overdue. If the belt goes, piston to valve contact will be very expen$ive to fix...
(160k on one/140k on my other)