Motorad 251-180 Engine Coolant Thermostat

180°F Thermostat for Mercedes-Benz Cooling Systems

The Motorad Standard 251-180 engine coolant thermostat is a direct-fit cooling system component built for Mercedes-Benz diesel applications that call for a 180°F opening temperature. It uses OEM-quality materials, a copper case, and a wax compound for quick reaction to coolant temperature changes.

Compatible With 1987-1998 Mercedes-Benz 300D, 300SD, 300SDL, 300TD, 350SD, 350SDL, S350, and E300 applications listed below, this thermostat is built to OE specifications and processes for consistent temperature control.

Key Features

• 180°F thermostat opening temperature for standard engine coolant regulation
• Copper case and wax compound for rapid response to coolant temperature changes
• Offset design with air relief valve
• Jiggle pin weep hole included for air bleeding during service
• OEM-style seals used where applicable
• Sealing flange outside diameter: 2.64 in.
• Bypass diameter: 1.64 in.
• Bypass length: 0.97 in.
• Flange thickness: 0.06 in.
• Motorad Standard line replacement thermostat, part number 251-180

Detailed Description

Motorad Standard 251-180 is an engine coolant thermostat engineered for Mercedes-Benz cooling systems that require a 180°F operating range. The offset design, air relief valve, and jiggle pin weep hole support proper coolant circulation and easier air evacuation after service. The copper case and wax element are selected to react quickly to temperature changes, helping the engine reach and maintain its intended operating temperature.

This part cross-references Gates 25180 for the same application. The 251-180 thermostat is listed for 1996-1998 Mercedes-Benz E300, 1994-1995 Mercedes-Benz S350, 1991-1993 Mercedes-Benz 300D, 1987 Mercedes-Benz 300D, 1992-1993 Mercedes-Benz 300SD, 1991 Mercedes-Benz 350SD, 1990-1991 Mercedes-Benz 350SDL, 1987 Mercedes-Benz 300SDL, and 1987 Mercedes-Benz 300TD.

What It Helps Address

• Engine running too cool or too warm due to thermostat wear
• Delayed warm-up after cold starts
• Temperature fluctuation from a sticking thermostat
• Air trapped in the cooling system after thermostat service
• Cooling system control issues on Mercedes-Benz diesel applications

Installation Notes and Tips

Verify the 180°F temperature rating and bypass dimensions before installation. The gasket or seal is not included, so inspect the sealing surfaces and use the correct seal or gasket for the application where required. The thermostat includes a jiggle pin weep hole and air relief valve, which should be oriented according to the vehicle service procedure to help purge trapped air.

For best results, install on a clean housing surface and refill the cooling system with the correct coolant mixture. Confirm fitment against the vehicle’s year, make, and model before service. Fits 1996-1998 Mercedes-Benz E300, 1994-1995 Mercedes-Benz S350, 1991-1993 Mercedes-Benz 300D, 1987 Mercedes-Benz 300D, 1992-1993 Mercedes-Benz 300SD, 1991 Mercedes-Benz 350SD, 1990-1991 Mercedes-Benz 350SDL, 1987 Mercedes-Benz 300SDL, and 1987 Mercedes-Benz 300TD.

Quality Assurance

Manufactured by an OE supplier using OEM-quality materials and safety standards, this thermostat is built to OEM specifications and processes for dependable cooling system service.