LOSTAR Coolant Overflow Reservoir Bottle Tank for 2008–2017 Kenworth & Peterbilt Trucks, Direct-Fit Replacement with Cap

The LOSTAR Heavy Duty Coolant Overflow Reservoir (603-5403) is a direct-fit replacement expansion tank engineered to restore proper coolant recovery on compatible 2008–2017 Kenworth and Peterbilt trucks.

This replacement radiator overflow bottle is manufactured from durable plastic and supplied with a matching cap so you can swap out a damaged or leaking tank quickly. Engineered to meet original-equipment form and fit, the part is designed for trucks equipped with Cummins or CAT engines and matches dealer part number N5346001. Whether you need a one-off repair or you're stocking parts for a fleet, this reservoir offers a reliable, affordable option to get cooling systems back to working order.

Which truck models and years will this reservoir fit?

The LOSTAR overflow bottle is made for model years 2008 through 2017 and fits many Kenworth and Peterbilt chassis. It covers widely used model families so you can confirm compatibility before purchase.

• Fits 2008–2017 Kenworth and Peterbilt trucks
• Compatible model examples: T660, T680, T600, T800, T880, W900
• Also fits several 300–399 series models such as 335, 348, 367, 377, 384–389
• Designed for trucks with Cummins or CAT engines only

How does this replacement part compare to the original dealer component?

This LOSTAR bottle is produced to match the size and mounting points of the original so it installs without modification. It replaces dealer part number N5346001 and comes brand-new with a cap included.

• Direct-replacement dimensions and mounting alignment
• Includes matching cap for a complete repair
• Plastic construction tested to quality-control standards
• Sold as a single, ready-to-install unit—no additional parts required

What are the practical benefits of installing this overflow bottle?

Swapping a damaged or brittle coolant reservoir restores proper coolant recovery, reduces leaks, and helps maintain system pressure. The new bottle helps protect the radiator, hoses, and engine from overheating risks associated with loss of coolant.

• Stops leaks from cracked or warped overflow tanks
• Maintains correct coolant level for efficient heat management
• Prevents air entry into the cooling system, promoting stable performance
• Quick bolt-on replacement minimizes downtime for repairs

What should you check before ordering and during installation?

Verify your truck’s model year and engine type (Cummins or CAT) and compare mounting points to ensure fitment. During installation, inspect hoses, clamps, and the cap seal to prevent future issues.

• Confirm year range: 2008–2017 and specific model compatibility
• Verify engine type: Cummins or CAT required
• Inspect and, if needed, replace radiator hoses and clamps while installing
• Ensure cap seals properly and torque fasteners per service instructions

Who is this for: Truck owners, fleet maintenance managers, and professional technicians who operate or service 2008–2017 Kenworth and Peterbilt trucks with Cummins or CAT engines and need a dependable, OEM-style coolant overflow reservoir. If you’re replacing a cracked, leaking, or aging tank and want an economical direct-fit unit that matches dealer part N5346001, this LOSTAR reservoir is sized and supplied to make the repair straightforward.