15w40

Still got the spark plug...

This is from cat.

 

The first # is the cold rating , the second is the viscosity measured at operating temp .... They are different tests.

Going lower on the First # will never hurt any motor...actually it usually improves the life because oil gets to moving Parts faster on Startup .... However, it usually comes at a price for the oil because it requires viscosity index improvers that cost money

The more critical number is the second number because that's where the engine generally lives at under operating temperature and load.

A synthetic oil will more precisely hold the stated viscosity with less drifting up/down from thermal effects.

 

The Cat syn oils are really good performing oils

 

I'd go 5w-40 cat syn... Still a 40 at operating temperatures but much better cold flow when you hit the key

 

I should start using 10w40 or 5w40 for spring/summer.

 

I think you mean 15w40 conventional oil or 5w40 synthetic....

And either would be fine.. (I prefer synthetic)

 

synthetic. For the 14.6 c15. I meant 10w30

 

Use the 5w40 either cat or rotella T6

Year round.......

Conventional oil use 10w30