Well, I got bored the other day, so I grabbed my freezer thermometer, and a quart each of Pennzoil 10w/5w30 and stuck them in my basement freezer for the day. I cranked that pupy up as cold as she would go. When I ckecked it out later, it was 5 degrees below 0 F. Ahh ha, perfect cold staqrt pumpibility testing weather in my freezer (if only I could put my car in there
). Well, the Pennzoil 10w30 was STIFF. I mean, practically no movement at all. Once it did get moving and sloshing, it moved a bit better. The 5w30 Pennzoil on the other hand flowed awesome, **** near still like Mobil 1. NIGHT AND DAY difference. If I took both quarts of oil in my hand and flipped them, the 5w30 instantly went to the other side, while the 10w30 ran like cold Mollasses and took a good 5-6 seconds to drain from one side of the bottle to the other. Well, I awnsered my own questions in some of my previous posts. 5w30 Pennzoil for winter it is. I won't do 10w30 in temps below about 10-20 degrees I'd say, based on how viscous the stuff was compared to 5W. Cheers