I get the max temp discussion, too hot is bad ... but when its cold out, how long should I idle to get the temperature above ... what temp? Is 65F ok to start driving? 45? I have a post-radiator tranny cooler installed, and am planning to tow a 5000 lb travel trailer to Maine and upstate NY, leaving in September and returning in late November, using a 5.3L Trailblazer. There is no aftermarket bypass installed, and I guess that is the question here. I've towed 12,000 miles thru the rockies with no problem, but other than a late season blizzard in Yellowstone, never been in any cold weather. I live in Florida.