I have a 95 SC 400, had her for 3 years and had timing belt, water pump and 90,000 mile checkup and replacements done. She now has 134,000 miles and a problem. She's leaking coolant somewhere. When I start the car everything is fine, about the time the temp gauge reaches midway the heat comes on if there is enough antifreeze in the system. That's when white smoke starts coming out from under the hood. The car never overheats or even gets past the midpoint in the temp gauge. I have replaced the upper and lower radiator hoses hoping that it was a dry rot problem.......it wasn't. I took it to a mechanic that usually works on her and was told it was the radiator and $500 to fix it. After reading some posts here I'm not quite convinced. The mechanic has in the past charged me $50 for a $2 piece of plastic. Feel like I need a second opinion, any help?