Currently GMC markets two truck lines, the Sierra and Canyon, but their earliest truck models stretch all the way back to the 1910s. These trucks all use a radiator to help cool the engine and keep it at a constant operating temperature. Radiator fluid circulates through the truck's engine, absorbing heat from the engine. The fluid releases this heat out to the surrounding atmosphere as it then passes through the radiator. Because the radiator is such an important part of the engine, it's important to service it properly. Flushing a GMC truck radiator will help get rid of any deposits in the engine.
Park your GMC truck in a flat location. You will need plenty of room to work around the front of the truck, so ensure that it is not parked next to a wall or other surface. Shift the transmission into park (on automatic models) and put on the parking brake. Shut off the engine and remove the keys from the ignition.
Pop open the hood. Prop the hood open with the hood catch. Allow the engine at least half an hour to cool.
Open the radiator cap. Depending on your GMC truck model and radiator cap type, there may be a lever which you first have to lift before you can remove the cap. Remove the cap by turning counter-clockwise. If the cap stops moving, press down with your palm while turning at the same time. Lift the cap out of the radiator.
Place the drain pan underneath the drain cock on the underside of the radiator. Open up the drain cock and allow the fluid inside to drain into the pan.
Remove the radiator overflow container and hose. Drain these into the pan. Rinse each out with water from the garden hose. Replace in the engine when finished.
Close the drain cock. Fill the radiator with water from the garden hose. Insert the keys into the ignition and start the engine. Empty the fluid inside the drain pan into a another container while the GMC truck engine warms to operating speed.
Allow the engine to run for approximately 10 minutes. This allows time for the thermostat to open and circulate the clean water throughout the engine. Shut the engine off. Use the pliers to open the drain cock. Take care, as the water inside will be very hot. Drain all of the water out of the engine. Tighten the drain cock when finished.
Fill the radiator with a 50/50 mixture of distilled water and radiator fluid. Start the engine and allow it to come to operating temperature again. While the fluid is circulating, top off the radiator tank with the distilled water. Fill the reservoir with distilled water to the fill line. Replace the cap on the radiator.
