Have you been losing coolant? If so, suspect a leaking head gasket. If not, check the radiator to see if the cooling fins are plugged with bugs or debris, or if they are corroded. If they crumble like a rotten chocolate chip cookie, they aren't transferring heat to the air. The clue is the lower radiator hose will be as hot as the top one but not much heat will be blowing from the fan.
To check for a leaking head gasket, your mechanic can check for the presence of combustion gases at the radiator with a special tool. You could also add a small bottle of dark purple dye to the coolant, drive it a while, then check with a black light, especially at the tail pipe. The dye will show up as a bright yellow stain that you can follow to the source.
Thursday, October 13th, 2011 AT 4:38 AM