X4XZ Coolant Overflow Reservoir 603-973 w/Cap — Fits 2014–2018 Chevy GMC Cadillac Trucks & SUVs

The X4XZ 603-973 coolant reservoir with cap is a direct-fit replacement tank designed to restore proper coolant overflow control and pressure management for compatible 2014–2018 Chevrolet, GMC and Cadillac V8/V6 trucks and SUVs.

This replacement coolant overflow tank (OE# 603-973) fits a wide range of GM models including Silverado, Sierra, Tahoe, Suburban, Yukon, Yukon XL and Escalade from model years 2014 through 2018. Built from durable plastic and supplied with a matching cap, the reservoir accepts thermal expansion from the cooling system and helps maintain stable engine temperatures by returning excess fluid to the radiator as the engine cools. It’s sold as a single unit and matches common OE mounting points and hose connections for a straightforward swap.

Will this reservoir fit my vehicle?

Compatibility covers many GM pickups and SUVs listed for 2014–2018. Always compare the shape, hose locations and mounting tabs shown in the second main image to your existing tank before ordering to confirm fitment.

• Fits: 2015–2018 Escalade (6.2L), Escalade ESV (6.2L)
• GMC Sierra/Sierra 1500 models (4.3L, 5.3L, 6.2L) across 2014–2018
• Chevrolet Silverado/Tahoe/Suburban models listed for 2014–2018
• Compare OE# 603-973 or replacement numbers: 22856231, 13502354

How does this part affect cooling system performance?

The reservoir stores expanding coolant when the engine warms and returns it as temperatures drop, preventing air pockets and helping maintain proper coolant levels. A cracked or leaking tank can lead to loss of fluid, overheating risk and irregular temperature readings, so replacing a failing reservoir helps restore normal cooling behavior.

• Prevents coolant loss from overflow and evaporation
• Helps the system self-bleed air during temperature cycles
• Works with the radiator cap to control system pressure
• Reduces risk of heat-related engine strain from low coolant

What are the construction and quality features of the X4XZ tank?

The tank is molded from resilient plastic engineered to resist heat and road chemicals, with factory-style hose fittings and mounting tabs positioned for correct alignment. X4XZ tests these units for fit and function to match OE performance, though professional installation is recommended to ensure secure hoses and proper torque on the cap.

• Durable plastic body designed for prolonged thermal cycling
• Includes matching cap; sold as one complete reservoir unit
• Manufactured to match factory mounting points and hose ports
• Backed by 1-year product service and 24-hour customer support

How easy is installation and what should I check during replacement?

Installation is relatively straightforward for someone comfortable with basic vehicle maintenance: drain coolant to safe level, disconnect lower hose and electrical clips, unbolt the old tank and transfer fittings if needed. Inspect hoses, clamps and radiator cap condition while replacing the tank to avoid future leaks.

• Recommend professional installation if unsure about cooling systems
• Drain coolant to an appropriate level to avoid spills
• Verify hose orientation and secure clamps after fitting
• Refill and bleed the cooling system per manufacturer procedure

Who is this for: The X4XZ 603-973 coolant reservoir is aimed at owners and mechanics servicing 2014–2018 GM full-size trucks and SUVs that need a reliable replacement overflow tank—whether repairing a cracked or leaking reservoir, restoring coolant system integrity, or performing routine engine bay refreshes. It’s also suited for fleet maintenance shops requiring a durable, OE-matching part backed by a one-year service policy and responsive customer support.