At really cold temperatures a 0W will flow better than a 5W.
At less cold temperatures, the 5W may be thinner.
Were I you, I would use a 0W and be done with it.
That would be the best compromise, IMHO.
If your above the gell point you have to look at the SAE viscosity NOT the W rating. As shown on the (less than accurate) viscosity chart a 20 will have MUCH lower viscosity then a 30 in the areas of interest above -30C - REGARDLESS of the CCS numbers or W ratings. The W rating is more about the wax content , PPD % and % Long chain paraffinic in the stock. Remember PAO with it's attendant cold flow properties are not necessarily the best lubricant, but being able to pump and flow is better than not A 5w-20 Dino like MC SS (or pick U fave) would be what the OP wants in Maine.
Originally Posted By: c3po
Originally Posted By: Drew99GT
Originally Posted By: Nayov
I want the most watery-thin oil for winter and I don't care about its properties at operating temps.
Run straight MMO then.
Go with Castrol Edge 0W-20 and replace a quart of your motor oil with a quart of MMO.
Yes there is nothing lighter at the temps your going to see, closely followed by the Toyota 0W-20 and Honda 0W-20.
Originally Posted By: c3po
Originally Posted By: Drew99GT
Originally Posted By: Nayov
I want the most watery-thin oil for winter and I don't care about its properties at operating temps.
Run straight MMO then.
Go with Castrol Edge 0W-20 and replace a quart of your motor oil with a quart of MMO.
Or if you prefer conventional oil, run Valvoline 5w-20. In PQIA comparison of 5w-30 oils, Valvoline has the lowest cold temp viscosity number. Substitute 1 bottle with MMO as long as it's cold temp viscosity is not higher than Valvoline 5w-20.