One of the most common symptoms of the need to replace the heater core in a Dodge Ram 1500 is a sweet smell inside the truck, according to RepairPal. The smell is characteristic of a coolant leak; it means that vaporized ethylene glycol from the vehicle's cooling system is leaking in the vehicle.
As the leak grows worse, drivers often notice a coolant leak under the dashboard. This leak is sometimes just a few drops, but over time, it grows significant enough that the carpet and components under the dash become wet.
The additional moisture in the vehicle causes windows to fog, especially if the heater is blowing. The defrost cycle blows more moisture on the cold windshield, where it condenses.
While mysterious coolant loss is also an indicator of a blown head gasket, it also indicates the possibility of a heater core problem. The loss of coolant reduces the efficiency of the cooling system in keeping the engine at a safe operating temperature, resulting in radiator boil over and engine overheating.
The lack of heat in a vehicle also indicates trouble with the heater core, according to RepairPal. Sludge from the heating system plugs the coils, so the engine's hot water no longer passes through to heat the vehicle.