For extreme cold, I would run Maxima Ultra 0W30 (if my owner's manual spec'd a 0W30).

http://www.maximausa.com/produ...troke/maxum4ultra0.asp

 

Do a "SEARCH" for amsoil in rubicon.

Im on my second year using it. Love it. I also use it in my wifes recon.
This is only my opinion and you will here many on the subject of oil.
I have had no problems with it. Good luck and use the search to find out all you want to know about oil.

 

Thanks again and it's great to hear the knowledge and web links re oil and from those who have used the stuff. I called the Amsoil tech line and they didn't miss a beat in saying the 0W-40 4-stroke is alright for the Rubicon. We'll see and also how it performs in 80F weather as well as 20 below weather.

Klondiker

 

I'm curious to know if the synthetics make a noticeable difference in ease-of-startup situations with the Rubicon in cold weather. Does anybody have a before-and-after experience to share concerning this situation with the Rubi?

 

I used Amsoil 0W-40 synthetic throughout last fall and winter and the Rubicon started fine down to 20 below 0 - although I didn't use it much then, just started it to find out the engine turn over. It was a huge difference from the Honda GN4 I previously used. The GN4 didn't allow much turnover at temps just below freezing when I used it the previous fall, but the Amsoil 0W-40 worked fine. I'm finding out now that Amsoil is a PAO oil, still better than the basic oils, but better still are the ester based oils, such as Maxima Ultra and Redline (in black bottles, not the white). Pricey at around $18.00 a litre, Amsoil here is around $14.00