EVIL ENERGY Engine Coolant Reservoir Overflow Tank 15808716 15778387 Compatible with Chevrolet Avalanche 2500 GMC Sierra 1500 Hummer H2

Q: Which Silverado and Sierra 2500 HD or 3500 engines does the GMT800 Coolant Reservoir Tank fit?

A: The 15075118 Coolant Reservoir Tank is listed for 2001–2006 Silverado and Sierra 2500 HD and 3500 trucks, plus the 2007 Classic versions, but heavy-duty GMT800 trucks with the 6.6L Duramax diesel use a different reservoir (cross-referenced as Dorman 603-125). Before ordering for a heavy-duty truck, check the part number molded on the original tank. If the old tank shows 15075118, 15808716, 15778387, 603-102 or another listed number, this Coolant Reservoir Tank is the correct match.

Q: What comes in the box, and do I need to move the low-coolant sensor from my old tank?

A: The package includes one Coolant Reservoir Tank, one 15 PSI pressure cap, one coolant level sensor with a 2-pin connector, and one tube. On GMT800 trucks the low-coolant sensor sits in the bottom of the reservoir and is generally not sold separately, so there is nothing to transfer: plug the factory harness into the new sensor until the connector locks, and the tank is ready to fill.

Q: Why does my 2003 Tahoe show a low coolant warning at startup when the reservoir is full?

A: On Tahoe, Yukon, Suburban and Silverado models from this generation, a false low-coolant warning with a full tank and normal engine temperature commonly points to a failing level sensor inside the original reservoir. Because the sensor is part of the tank, the usual fix is replacing the complete Coolant Reservoir Tank. First confirm the level with the engine cold, then inspect the 2-pin connector for corrosion or a loose terminal, since a dirty plug can cause the same warning.

Q: When should a Suburban or Yukon XL owner who tows a trailer replace the coolant reservoir?

A: Replace the Coolant Reservoir Tank as soon as the plastic looks yellow and chalky, shows orange crust along a seam, or the coolant level drops between checks. For tow vehicles, inspect the tank before the towing season and before any long trip with a camper or boat, because a hairline crack that only weeps at idle can open up under the higher heat and pressure of climbing grades with a full trailer. Replacing an aging reservoir early costs far less than an overheating event on the road.

Q: Where do I add coolant on a GMT800 truck that has no radiator cap?

A: Many GMT800 Silverado, Sierra, Tahoe and Escalade models are filled through the pressurized reservoir rather than a radiator cap. Add coolant through the Coolant Reservoir Tank with the engine completely cold, and never open the 15 PSI pressure cap while the system is hot, because pressurized coolant can spray out and cause burns.
Q: How do I fill and bleed the cooling system on a 5.3L Silverado after installing the new tank?

A: With the engine cold, pour coolant slowly into the new Coolant Reservoir Tank. Leave the cap off and run the engine in short intervals of about a minute, topping off as the level drops. Raising the front passenger side of the truck slightly can help trapped air escape. Once the thermostat opens and the upper radiator hose feels hot, top off to the full mark, install the cap, and watch the temperature gauge on a short test drive. Recheck the level after the engine has cooled and again after the next few drives.

Q: What type of coolant should go into the GMT800 Coolant Reservoir Tank?

A: These trucks were factory-filled with Dex-Cool (orange). Use Dex-Cool or a coolant specifically labeled as Dex-Cool compatible, mixed with distilled water to the ratio in the owner's manual. Avoid topping off with traditional green coolant, because mixing chemistries can create sludge that coats the level sensor and clogs the heater core. If the system already contains mixed or discolored coolant, flush it completely when installing the new tank.

Q: Does the tank fit a 2007 Silverado or Sierra?

A: Only the 2007 Classic models. The 2007 Silverado 1500 Classic, 1500 HD Classic, 2500 HD Classic, 3500 Classic and the matching Sierra Classic trucks carried over the GMT800 design and are covered. The redesigned 2007 Silverado and Sierra (new body style) use a different cooling system layout and are not compatible with this Coolant Reservoir Tank. The Classic badge or the older body style is the quickest way to tell them apart.

Q: How long does it take to replace the coolant reservoir on an Avalanche or Escalade, and what tools are needed?

A: Most DIY owners complete the swap in about 45 to 90 minutes, including refilling and bleeding. Typical tools include a socket set, pliers for the hose clamps, a drain pan, rags, a funnel and fresh Dex-Cool. Work with the engine cold, release cap pressure slowly, disconnect the level sensor plug before lifting the old tank out, and catch coolant as each hose comes off. Clean up spilled coolant right away, since coolant is toxic to pets.

Q: Will the 15 PSI cap hold up on a Hummer H2 or a truck used for towing and off-road driving?

A: The included pressure cap is rated at 15 PSI (about 103 kPa), which keeps the Hummer H2 or GMT800 cooling system sealed and raises the coolant boiling point during towing, low-speed off-road crawling and hot-weather idling. Do not substitute a higher-pressure cap to stop coolant loss, because extra pressure stresses the hoses, radiator and reservoir seams. If coolant still escapes with a new Coolant Reservoir Tank and cap installed, pressure-test the system to locate a separate leak at the radiator, water pump or heater hoses.