Replacing a radiator in a GMC Sierra is am ambitious project. But, if you are mechanically inclined, you can save money by doing it yourself. Here's how to replace the radiator in a 1999 or later GMC Sierra with a gasoline engine.
Open the radiator and drain the fluids carefully into a resealable container. Remove the shroud bolts on the upper fan and remove the fan shroud. If your Sierra has an upper panel, remove the fasteners and the panel. If it has upper insulators, remove the insulators and the brackets.
Detach the radiator hoses. Inspect them carefully for any sign of wear, cracks or bulges, and replace them if necessary.
Remove the oil coolant lines and coolant recovery system lines. Remove the bolts holding the lower fan shroud, and remove the shroud.
Pull the radiator away from the lower brackets and lift it out of the vehicle. Install the new radiator on the brackets and tighten the bolts according to specifications. If your vehicle has upper insulators and an upper panel, replace them now.
Reconnect the oil coolant lines and coolant recovery system lines and reattach the radiator hoses.
Fill the radiator with a mixture of half distilled water and have engine coolant. Start the motor and let it run for a couple of minutes, then add more fluids, if necessary.
