We keep a total of 6 Farmall and Olivers in an unheated shed. During cold weather, every start of every tractor is accompanied by a light mist of sooty water droplets. It lasts for a minute or so until the manifold and muffler begin to warm. It's simply condensation from the spent combustion gases being blown out the stack. If you keep the muffler covered, the coolant level stays up and the tractor otherwise runs fine, I wouldn't worry about it. ...Bob M
PS - You would not believe the stuff that issues from the stack when I cold start the old Cummins diesel-powered Kenworth! You better be wearing dark clothes or else stand upwind when that lights off!