Dorman Front Pressurized Coolant Reservoir with Cap — Direct-Fit for Chevy/GMC 2500/3500 2001–2007

The Dorman 603-125 is a direct-fit pressurized front coolant reservoir with cap designed to replace the original tank on select Chevrolet and GMC 2500/3500 models from 2001–2007.

This replacement coolant expansion tank is manufactured to match the original equipment’s shape, mounting points and pressure-cap interface so it installs cleanly and performs like the factory part. Built from heat- and vibration-resistant materials, the Dorman 603-125 helps restore proper coolant containment and routing after a crack, leak or degraded reservoir requires replacement. Before ordering, confirm vehicle compatibility using your make, model and trim in the fitment tool to ensure an exact match.

Which vehicles is this reservoir compatible with?

The Dorman 603-125 is listed for a range of Chevrolet Silverado and GMC Sierra heavy-duty models and their Classic variants spanning model years 2001 through 2007. It covers both 2500 HD and 3500 applications for the specified years, but not every trim or engine option may be covered.

• Chevrolet Silverado 2500 HD and 3500 model years 2001–2006
• Chevrolet Silverado 2500 HD Classic and 3500 Classic for 2007
• GMC Sierra 2500 HD and 3500 model years 2001–2006
• GMC Sierra 2500 HD Classic and 3500 Classic for 2007

How does this Dorman reservoir match the original part?

This tank is engineered to replicate the factory part’s fit and functional features so it mounts and connects using the existing brackets, hoses and cap interface. Dorman designs replacements to minimize modifications at installation and to restore the intended coolant flow and pressurization.

• Engineered to match OE mounting points and hose connections
• Includes pressurized cap interface compatible with factory-style caps
• Molded from materials chosen to resist underhood heat and vibration
• No special tools or fabrication typically required for installation

What are the durability and performance features of this reservoir?

The Dorman 603-125 is produced from reinforced plastics formulated for long-term exposure to engine bay temperatures and coolant chemistry. The part is manufactured to resist cracking and leaks that can occur from thermal cycling and mechanical stress.

• Durable construction designed for heat and vibration resistance
• Precision molding to reduce stress points and potential leaks
• Designed to maintain coolant pressurization and overflow control
• Backed by Dorman’s aftermarket experience and quality controls

What should I check before buying and installing the reservoir?

Confirm exact fitment with your vehicle trim and year to avoid fitment issues. Inspect hose ends, mounting brackets and the cap sealing area for compatibility and make sure the replacement cap (if not included) matches the vehicle’s pressure rating.

• Use the vehicle fitment tool to verify make, model and trim compatibility
• Compare hose diameters and mounting bracket locations to the old tank
• Verify the cap pressure rating and replace the cap if required
• Drain and dispose of coolant properly when replacing the reservoir

Who is this for: The Dorman 603-125 reservoir is aimed at owners and technicians servicing Chevrolet Silverado or GMC Sierra 2500/3500 trucks (2001–2007) who need a reliable, OE-style coolant expansion tank replacement. It suits anyone replacing a cracked, leaking or otherwise failed reservoir who wants an affordable, direct-fit aftermarket option designed to restore proper coolant containment and routing without custom modification.