We're not trying to scare you, but any time you have your car or truck heater on, you have scalding hot water traveling through the heater core in your passenger compartment only inches away from your feet. The water that travels through the heater core is actually engine coolant, the same green or orange stuff that runs through your radiator. Since your engine produces so much heat that has to be expelled anyway, the engineers decided to send it through a heater core to warm the passenger compartment instead of using an electric or gas-fired heater. It's a great idea as long as the system, heater core included, works correctly, which it usually does. But as your car or truck ages, the heater core suffers from the same problems that your vehicle?s radiator suffers from: corrosion and leaks. Corrosion in a radiator or heater core is primarily due to a lack of coolant changes. If you've changed your antifreeze religiously every two years or so, you may not have any crud built up in your heater core. If, on the other hand, you're going on 80,000 miles without a coolant change, your heater core may look like Marlon Brando's coronary arteries. Leaks in your heater core come as a result of corrosion, either from the acidic coolant eating away at the joints of the heater core or from the additional pressure that results from a blocked heater core weakening the joints. Either way, it's not good. Once your heater core begins to leak, interior damage, foul odors, mold, and rust are close behind. And even if it's not leaking, a blocked heater core can significantly reduce the amount of heat you get on those cold mornings, making your car unpleasant to drive. The bottom line: If your car is losing coolant but you can't figure out from where, if your carpets seem damp for no reason, or if your car is putting out substantially less heat than it was before, get the heater core checked out. After all, a new heater core is far less expensive than new carpet and floor pans!