Chevrolet Repair: 1996 4.3 liter chevy coolant?, head gasket, liter v6

Question
sir,
my 1996 chevy 4.3 liter v6 has 155K miles.  after driving for some distances, i.e 20+miles, when i stop, i smell coolant, but nothing is dripping from the engine, the overflow resevoir, or anywhere.  when the heater is on, the air smells like coolant (youknow that hot radiator smell).
the engine has never run hot and it stays within the 140-200 degree range, never running hot, although i have to add coolant every so often. a friend says my block is cracked and the coolant is going out of the exhaust. i change the oil regularly and do other things to help keep the truck in good condition (brakes, rotate tires, serpentine belt, etc..)
what do you think?
thank you for your time,
chris in new orleans

Answer
Hi Chris.... do you have coolant smell in the cab....check heater core for a possable leak....if you think it is burning coolant, pull the plugs and look for discoloured ones...could be head gasket. if you suspect the heater core pull heater box and see if it is wet inside. there is a drain in them and coolant could be escaping out there and running down firewall then dissapearing as you drive. hope this helps