Dayco 71603 Radiator Coolant Hose - Lower

Dayco 71603 Curved Radiator Hose

The Dayco 71603 curved radiator hose is a lower coolant hose built for select BMW and Mercedes-Benz applications that require a dual I.D. fitment. Made from EPDM rubber and finished in black, it is shaped to route coolant cleanly through the engine bay while matching the original hose path.

Dayco’s Curved Radiator Hose line focuses on application-specific cooling system replacement parts for vehicles that need accurate bends, proper hose sizing, and dependable coolant transfer. This hose follows that approach with a dual inside diameter design and SAE J20R4 Class D-1 / SAE J1684 Type EC compliance.

Key Features

• Part number 71603 for application-specific cooling system service
• Curved lower radiator hose design
• Dual I.D. hose with 1 1/2 in. end 1 inside diameter and 1 5/8 in. end 2 inside diameter
• EPDM construction for coolant hose service
• Black finish
• Built to SAE J20R4 Class D-1 and SAE J1684 Type EC specifications
• No heat shield and no protective sleeve

Detailed Description

This Dayco radiator coolant hose is engineered for lower hose routing on select BMW 535i, BMW 735i, BMW 735iL, and Mercedes-Benz CL500, S420, S500, 400SEL, 500SEC, 500SEL, and 400SE applications. The curved profile helps maintain the factory-style coolant path, while the EPDM material is suited for standard radiator hose service in the cooling system. If you are replacing a worn lower radiator hose on a BMW 735iL or Mercedes-Benz S500, part number 71603 provides the correct dual-diameter configuration for the listed vehicles.

This part cross-references Gates 21890 for the same application.

What It Helps Address

• Coolant leaks from a cracked or aged lower radiator hose
• Softening, swelling, or collapse of the original hose
• Improper hose routing caused by a damaged curved hose
• Cooling system service on BMW and Mercedes-Benz models with dual I.D. hose requirements
• Replacement of a hose that no longer seals correctly at the radiator or engine connection

Installation Notes and Tips

Verify the end diameters before installation, since this hose uses different inside diameters at each end. Confirm lower hose routing against the vehicle’s original layout on the listed BMW and Mercedes-Benz models, and inspect clamps, necks, and adjoining cooling system components for wear before reassembly. After installation, refill and bleed the cooling system according to the vehicle service procedure.

Quality Assurance

Dayco manufactures this hose to SAE J20R4 Class D-1 and SAE J1684 Type EC standards for radiator coolant hose service. The EPDM construction and application-specific curved design support consistent fitment on the listed vehicles, including BMW 535i and Mercedes-Benz S500 lower hose applications.