Winter Generator Oil

[repairman54]

A zero bottom number is a must to pull over a gen set at real cold temps.
I tried 5-30 synth. in my 10hp Craftsman stored outside. At zero F you would lift the gen set off the ground trying to pull it over to start it and never get it to spin over fast enough to start. 0-30 synth. in it spun over and fired right up.
Only use 0-30 synth. now in my stationary Generac as I need dependable starts at minus 30 F.

 

[Doc8404]

I run Castrol 0w40 since I have it on hand for his ATV

 

[mark pruett]

I always figured a 0w30 was lighter than a 5w30 or 10w30, but from reading, that may not be the case.

Sort of... the 5w-30 nomenclature essentially says that at a specific hot temp (100C / 212F) it has the viscosity of a 30 weight oil. So a 0w-30, 5w-30 and 10w-30 all have hot viscosities that are within the same "30 weight" band (between 9.3 and 12.5 centistokes).

When they're cold, they all differ- basically it's about how easily they pump at various temps. Here's a set of tables that shows how it works:

https://wiki.anton-paar.com/en/sae-viscosity-grades/

So in your case, where it's started in very cold temps, you probably can't go very wrong getting the lowest "w" rating you can, as long as the upper "hot" number is 30 or 40.