Dorman Engine Coolant Reservoir Replacement Tank with Cap — Non-Pressurized Direct-Fit for Select Cadillac/Chevrolet/GMC — Heat-Re

Dorman 603-100 is a direct-fit, non-pressurized engine coolant reservoir with cap designed to replace the factory overflow tank on select Cadillac, Chevrolet and GMC models.

This replacement coolant reservoir is molded from durable plastic and built to match the original equipment’s fit and function so you can restore coolant containment and maintain proper system appearance. Dorman’s design aims to resist the heat and vibration found in the engine compartment while providing an accessible fill point and reliable mounting points. The part ships with a matching cap and aligns with factory hose connections for an easier installation compared with aftermarket universal tanks.

How does this reservoir match my original equipment?

The Dorman 603-100 is engineered to mirror the factory tank’s dimensions, mounting bosses, and hose inlet/outlet locations. That close fit reduces modification time and helps preserve factory routing for hoses and brackets. Parts that follow OE geometry also help avoid interference with nearby components under the hood.

• Direct replacement shape and mounting points for select Cadillac, Chevrolet and GMC vehicles
• Cap included with the reservoir to match original fill method
• Hose connection locations engineered to align with OEM hoses

What materials and durability features does the tank offer?

Manufactured from quality automotive-grade plastic, the reservoir is designed to withstand common underhood stresses like heat cycling and vibration. The material resists warping and cracking that can develop over years of thermal exposure. Dorman leverages aftermarket experience to optimize wall thickness and reinforcement where it matters most.

• Heat-resistant plastic designed for continuous engine-bay exposure
• Reinforced mounting areas to resist vibration-related wear
• Factory-style cap to maintain sealing and convenient filling

How straightforward is the installation process?

Installation is typically straightforward for anyone familiar with basic underhood maintenance: drain the system as needed, unfasten the old reservoir, disconnect hoses and electrical connectors, then swap in the Dorman unit. Because it’s a direct replacement, no trimming or bracket fabrication is generally required. Always verify fit for your exact model and follow vehicle-specific service steps to avoid spills and ensure proper reassembly.

• Many installations are bolt-in with original fastener locations
• No special tools required beyond standard hand tools and coolant catch pan
• Use the vehicle’s service guide or Dorman’s fitment tool to confirm compatibility

Will this reservoir control coolant levels and leaks like the original?

The Dorman 603-100 is intended to restore the visual appearance and liquid containment of the factory tank. While it is non-pressurized and relies on the vehicle’s cooling system design, it provides a sealed fill cap and proper hose interfaces to help prevent leaks when installed correctly. It’s built to replicate the original part’s behavior, not alter system pressure characteristics.

• Sealed cap design to limit evaporation and splashes
• OEM-aligned hose fittings help reduce leak points
• Manufactured to meet aftermarket durability expectations

Who is this for: The Dorman 603-100 is aimed at DIY mechanics, independent shops, and vehicle owners who need a cost-effective, direct-fit replacement for a cracked, discolored, or leaking coolant overflow tank on select Cadillac, Chevrolet, or GMC vehicles. Choose this reservoir when you want an OE-style fit, a supplied cap, and a durable plastic construction that withstands routine underhood conditions. Always confirm exact vehicle fitment using your make, model and trim level before purchasing.