10W30 or 15W40???
 

Its time for my oil and fuel filter change.
Should I switch to 10W30 oil for winter? I've heard that 15W40 might be a little heavy for Wisconsin winters.
2005 PS 6.0 liter CC FX4
Any input is appreciated! Thanks

No -- switch to 5W-40 syn. Handles the extreme temps much better than dino oil. Try this: Buy a quart of those three oils and put them in the freezer overnight. Take them out and pour... You'll be amazed.

Take Izzy's advice and switch to 5W-40 synthetic. The synthetic is extra money, however good quality clean oil is essential to your 6.0 and IMO the extra dollars are worth it for the long haul.

Synthetic 5w40 on a 6.oh.

no matter what you change the winter weight to, the warm weight should stay the same...

get something that is XXw-40.

5w-40 rotella for sure.

15W40 is a summer weight oil. I've never seen documentation for the 6.0L, but I would guess that the cold start rating using this oil is 0F (-18C).

You will have to switch to lighter weight oil for winter in Wisconsin. 10W30 is fairly standard for diesels. However, you could use anything that is suitable for the 6.0L engine. The basic goal is to use oil that will allow you to start the engine at temperatures you expect. The electric jacket water heater can be used to aid starting in very cold weather such as -15F (-26C) and below.

15w-40 will have the same viscosity as straight 15 in the freezing range...

it will have the same viscosity as straight 40 in the operating range...

again I'll suggest that you stick with a _w-40 oil to keep the same 40 at operating temp, as operating temp won't change much even with a lower external temp.

I've been switching to 10w30 for my winters here in Alberta. Make sure the oil your buying is at least CI-4 rated for diesels. I don't bother with the synthetics due to the price and the frequency of the changes I do. Which is nothing against the synthetics, it's just not for me. The 15w40 is going to give you some problems in the winter. (not sure how cold Wisconsin gets) Here -35C to -45C not that unusual. Even on the dino oil, this has been serving me well for the last 4 years on my truck. Plug it in when it's cold and don't idle it much.

Another vote for Synthetic 5w40.