My 95 Metro has begun overheating. I've replaced the thermostat without effect. My radiator was leaking a few years ago and I used a chemical sealant. Thought maybe the radiator was plugged so I pulled an almost new one from the junkyard. No change. Recently the water pump began leaking. I replaced the water pump and put in a new timing belt at the same time. It still overheats. I'm at a complete loss as to what can be the problem. The coolant seems to be flowing okay and I get a hot intake hose as well as exit hose from the radiator. I can drive for short trips okay but after about 15 minutes it will overheat and the coolant boils out. Any suggestions as to what I should check?