Cold Day? Keep Warm in Your Chevy or GMC Truck with a New Heater Core! Even with cooler weather, there are still plenty of nice days to enjoy cruising in your classic Chevy or GMC truck. Make sure you're kept warm and comfortable -- and that your defroster works properly -- by replacing your clogged or leaking heater core. We have them for all 1964-72 Chevy and GMC trucks, with or without air conditioning.