Heater Hose

Position a bucket with a capacity of at least two gallons underneath the radiator and directly below the drain plug. On the GMC Sierra, the drain plug is usually on the bottom passenger side of the radiator.

Open the drain plug and allow the cooling system to drain completely. Once complete, pour the old coolant into a sealable container for proper disposal.

Loosen the hose clamps and pull them back from their connections to the engine and the heater core. You'll need either a screwdriver or pliers, depending on the type of hose clamp. The heater core is behind the engine and up underneath the windshield. The heater hoses dead end at the firewall between the engine and passenger side of the GMC Sierra.

Make a few lengthwise slices on the heater hose with a knife. You should never try to pull or twist the hose off without these cuts, as that can damage the heater core.

Remove the old heater hoses and scrape away any leftover debris on the fittings. Next, place a bit of gasket sealer on the fitting but don't place any on the inside or outside of the new hoses.

Place the hose clamps on the new heater hoses and slide them into place over the fittings. You may want to replace the clamps as well, as they can wear down over time and also cause leaks. Be certain there's enough hose on the fittings to secure the clamps.

Tighten the hose clamps, refill the radiator with fresh coolant and start the engine of the GMC Sierra. Let it run for about 15 minutes to check for any leaks from the new heater hoses.