An oil change removes alot of it. But its not going to remove all of it. Plus as soon as the short trips begin again, so does the sludge..You're doing the right thing by staying on top of this and cleaning the hoses. Those brutally cold temps don't help at all. I did 2 oil changes in 2 days. (Not on purpose, its a long story, but it did remove alot of sludge) I'm in a warmer climate than you so I'm waiting for spring right around the corner and I won't have this problem until probably next winter. You may also consider switching to 0w -40 oil in the coldest months. I will be switching to 0w -40 before next winter, and I expect better results. Don't get me wrong, switching to this oil doesn't mean you can drive short trips all you want and think everything is solved but it will help tremendously.