Check the carpet and floorboard on the passanger side for coolant leak from the heater core.. Simply using the heater would NOT cause a leak as the coolant flows thru it at all times.. However using it will flow the incoming air over the core and give you the smell of coolant if there is a leak...small or large.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist