Coolant leak. Coolant visible just above engine block (head gasket, maybe) and a small puddle appeared directly under that overnight. Probably a few ounces. Had topped off radiator and reservoir a couple of days before. Wife detected odor when we returned from outing. After 35 miles in town and stop and go, the radiator was not even hot, just barely warm. I removed radiator cap and ran engine at a couple thousand rpm for 5 minutes or so. The thermostat must have opened since there was flow in the radiator. I'm guessing the water pump works also, since there was flow in the radiator. What is the most likely source of the leak?