I changed my oil about 6000kms ago using Quaker State Conventional 5W-30. Living in Canada I was wondering if I could use 0W-30 when I'm soon to change my oil being that we can get to -50c in the winter months. I know the viscosity of the oil doesn't change but I can't find anything on the internet about others doing this. Any help would be great!

 

I generally wouldn't, especially on an older engine where clearances generally get bigger so you need a thicker oil to help "fill" those clearances, although you are still staying with a 30 warm viscosity, so it shouldn't really make as much difference. If you are experiencing hard starts you might consider it, but if you are using the truck for short drives in cold weather I would stay with the 5W-30 so your engine doesn't experience insufficient lubrication during those short drives where you may not reach operating temperature.