5W40 or 15w40?

0660BigHoss · #1 (**permalink**) 08-21-2011, 08:16 AM

I know I want to run full synthetic. But living in AZ, should I run 5w40 or 15w40? It can get hot as crap here in the summer, but it can also get below freezing in the winter. We also plan on taking it to the mountains at least a few times in the winter where it can get well below zero.

Just wondering if one might be better to run than the other.

Thanks in advance!!

Aussiekeeper · #2 (**permalink**) 08-21-2011, 10:00 AM

I use Schaeffers 5w40 9000 series oil. It get cold and hot here (+105) in San Diego. I know it gets hotter there.....Schaeffers is very good oil.

bwillis2003 · #3 (**permalink**) 08-21-2011, 10:09 AM

Id run 5w-40 regardless, but ya if you get that cold, Id def run it. I used to run Rotella, Im going to try Valvoline this time. Apparently it's a lot better. Main thing is, keep your oil changed when its supposed to be.

worldwide73 · #4 (**permalink**) 08-21-2011, 10:41 AM

Just changed mine today 15w40 semi-synthetic. Change before it gets cold again probably to 10w30 semi-synthetic then.

smokersteve · #5 (**permalink**) 08-21-2011, 12:08 PM

Quote:

Originally Posted by 0660BigHoss

I know I want to run full synthetic. But living in AZ, should I run 5w40 or 15w40? It can get hot as crap here in the summer, but it can also get below freezing in the winter. We also plan on taking it to the mountains at least a few times in the winter where it can get well below zero.

Just wondering if one might be better to run than the other.

Thanks in advance!!

you can run both. Durring the winter 5w-40 will be better becasue it has the lower viscocity. 40w is 40w, ther is no difference, why? becaue 15w-40 is the same as 5w-40 when it is warm. the first number is for cold operation, 5 is thinner than 15 when it is cold.

if you dont drive that much to where you change your oil twice a year, just use 5w-40. if you do, then change to 5w-40 for the winter, then back to 15w-40 durring the summer because it is cheaper. you can do what ever you want.

**windrunner408** · #6 (**permalink**) 08-21-2011, 12:14 PM

I've had my truck since it was new and have run Amsoil 15w-40 HD Diesel & Marine Fully Synthetic oil since my first oil change at 7000 miles and have had my truck in temperatures well below freezing but not below zero at least when I tried to start it and have had zero problems. Now after I started it I let it run for a few minutes before I drove it but never had any problems. Not saying Amsoil is the greatest thing since sliced bread but it has worked great for me and I run it in everything from truck to my car and jeep and harley davidson. I even run it in the differentials. I would say that unless you are going to be in extreme cold, like say below 0 then I would run 15w-40. Otherwise just change it before you get into the cold and once you come out of the cold.

**sbarbee54** · #7 (**permalink**) 08-21-2011, 02:40 PM

5W-40, especially if you are going to take it to the mountains... I live near Tahoe and went up there for new years a couple years back. With the 15W-40 it was a son of a gun to start, it cranked and started on the first try but wow did it Cranked slower than a old lady in a wheel chair though. Have been up in about the same temp with the 5w-50 T6 and it is a world of diffrence. Like everyone says change it every 5K is the most important.