Hey guys im heading up to the mountains and it's going to get ~18deg F in the lowest at night. Probably 20-25 in the morning.

I am running Rotella T5 15W-40 because I live in a warm climate. Only going to be in the mountains for a couple days. Should I change the oil to a thinner viscosity?

Thanks,

 

I wouldn't but have been abusing most of my vehicles for years using 20w-50.
......

 

Dang i'm freaking out here lol. Thinking im going to go grab some T5/T6 10W-40.

 

I've never had a single problem with 15w40 in those temperatures.

 

I wouldn't recommend doing it for months/years on end, but you'll be fine. It'll just clatter a little for a few seconds.

 

I've used 15w-40 year round in central Idaho where the temps are between 0-100f. Never had any problems.

 

Think this answers a lot of ?’s

 

This chart only shows the oil's rated temp ranges, meaning the temperatures where they are inside their rated weight. It doesn't take into account each individual manufacturer's engine tolerances.

I still say that 15w40 is the perfect weight for warmer climates, but I won't use it under 20* (for extended periods) because of the clattering I've heard my engine make with 15w40 under that temp.

 

From the 03-04 owners manual.

 

I'm glad there is finally an oil thread! This is valuable information. Nothing like this has ever been discussed before, especially on the internet. *(runs, ducks, and hides)*

I kid. I prefer 5w/40 myself. Rotella T6. 15w/40 is fine, but I just don't like it in sub freezing climates. Cheers!