I apologize for the long winded post but the other day I had to use my truck. 2013 LML Sierra with 158K kilometres on it. Outside temperature was about -17c. Truck was not plugged in. Started truck and let it warm up about 10 minutes. Hooked up my sled trailer and noticed some coolant in the snow. Checked level and it was down. I proceeded to add more coolant but when I loosened cap antifreeze spilled over into the fender side of overflow tank. I topped it off and parked it. Fast forward 4 days later I had to use my truck to take my wife to work as we had a snowstorm. Outside temps were -26c and truck wasn't plugged in. It started no problem and let it warm up a half hour. About 40 kilometres into the trip my low coolant warning came on. Checked coolant and engine side was low and fender side was half full and AF was leaking on the ground under RH fender. Pulled it into shop and liner around overflow tank was soaked with AF. Pulled cap slowly to let air out. We pressure tested the system and it checked out. Topped up the AF and I left for home and checked it twice at the side of the road. By the time I got home it was down a bit. Did not see coolant in snow where it was parked. Temp guage in the summer had never hit the 100 mark unless I was towing. In winter it's a high as the summer reading not towing. Any ideas what's going on here? What to check for?
