Radiators

Early Bronco radiators are available in factory-replacement aluminum and copper/brass units, as well as high-capacity aluminum radiators for builds with upgraded engines or AC systems. Tom's Offroad stocks radiators designed to fit the 1966–1977 Bronco's engine bay dimensions, with options for standard 2-row and high-performance 3-row cores.

To drain the coolant on an early Bronco, locate the petcock drain valve at the bottom of the radiator and open it with the engine cold. Place a catch container below the drain. If no petcock is present, disconnect the lower radiator hose. Allow the system to fully drain before flushing and refilling with fresh coolant mixed to the appropriate 50/50 antifreeze-to-water ratio.

Early Broncos with cast iron engines use conventional green antifreeze (HOAT or IAT formula) mixed 50/50 with distilled water. Avoid using extended-life OAT coolant (orange or orange-red, like Dex-Cool) in older cast iron and aluminum combinations without confirming compatibility. Change coolant every 2 years or 30,000 miles to maintain corrosion inhibitor effectiveness.

Signs that an early Bronco radiator needs replacement include visible corrosion or cracks in the core, coolant leaks at the tank seams, overheating despite proper coolant level and thermostat, and internal blockage causing poor flow. A pressure test will reveal most leaks. If the core is more than 50% blocked on a flush test, replacement is more cost-effective than cleaning.

An aluminum radiator is a worthwhile upgrade for any early Bronco, especially those with performance engines or air conditioning. Aluminum transfers heat more efficiently than original copper/brass units, dissipates heat faster, and is significantly lighter. A quality 2- or 3-row aluminum radiator from Tom's Offroad will outlast a rebuilt original and improve cooling margins on hot days and steep trails.