yea i live in a wide ranged climate called Buffalo, NY haha. My uncle is from CO but I use 20W-50 in summer and 10W-40 in winter. Both being Castrol GTX high mileage or the full syntec. 20W50 is a bad bad idea for cold climated like ours in winter!! But it works well in hot summers. Keeps the oil pressure good and mine have always run great with it. Come to think of it I used 20w50 when I bought my old bimmer this summer but the weather is aldready starting to drop so I better get on that oil change back to 10w-40 soooon! Hope this helps.