My son changed oil in his 200 ford focus and used 10w30 M1 for high mileage engines. The engine has 65K miles on it. I noticed the other day when we were changing the upper CO2 sensor that it had some chatter in the top end for a few seconds, and then quietened down. We live in North Carolina where we get some cold weather in the 20's, during Jan. and Feb. Should he go back to the 5w30 minus the high mileage oil? Does anyone thing the 10-30 is a bad thing?