I’ve alwyas been running 5w30 full synthetic or dexos in my hummer h2 with about 240,000 Kms but last winter was super cold between -25c to -40c daily with the truck being parked outside. Was thinking of running redline 0w30 or any other 0w30
good choice? Or is it bad to switch the weight since my truck has always been fed 5w

thanks

 

I have always been a big Mobil 1 fan but this year I have switched to Amsoil synthetic for everything I have. I watched a few cold tests on YouTube and I was surprised with the results on more than a few tests. Oil is a funny thing and it has a cult like following. Keep it clean and changed and you will be fine

 

As it happens I run Mobil 1 0W-40 here in the UK so not being a lubricant expert I pulled up this link which explains the basics and the numbers:

Also this section from the manual:-
If you are in an area of extreme cold, where the temperature falls below -20°F (-29°C), it is recommended that you use either an SAE 5W-30 synthetic oil or an SAE 0W-30 oil. Both will provide easier cold starting and better protection for your engine at extremely low temperatures.

 

Yeah if you are getting temps that low than changing to a 0W might be a good idea.

I've been running Amsoil for years as well. Project Farm on Youtube recently did a number of videos on testing a bunch of brands including Penrite, Mobile 1, Red Line, Royal Purple, etc and Amsoil won. This is one of them.