How to Add Coolant: 2025 GMC Sierra 2500 HD AT4 6.6L V8

Adding engine coolant (also known as antifreeze) to your 2025 GMC Sierra 2500 HD is pretty easy. Engine coolant / antifreeze circulates through your engine to keep it cool in the summer but won't freeze in the winter. Make sure to check your engine when it is cold for an accurate reading. The video above shows you where the coolant reservoir in your Sierra 2500 HD is located and how to add coolant / antifreeze. Be sure to check your owners manual to determine the correct type of fluid to add - for GMCs, it will typically be in a section titled Fluid Capacities in the back of your manual. Mix the coolant / antifreeze with distilled water so that you have a combination of 50% coolant and 50% water. Some coolants will come premixed-that is, you don't need to add any water. These coolants will typically say 50/50 or pre-mixed on the front of the coolant bottle.

Removing the coolant reservoir cap on a warm engine could cause the cap to fly off at a high rate of speed and fluid to spray out of the reservoir. Always wear safety goggles when working on your Sierra 2500 HD. Promptly wipe up any spilled fluid as it is highly toxic. Animals love its sweet taste, so even a spilling a small amount on your garage floor can end up in the dog's stomach pretty quickly. If you notice an oily surface in your coolant, immediately have your mechanic inspect your Sierra 2500 HD for head gasket leakage