Motorad 251-185 Engine Coolant Thermostat

OE-Style 185°F Thermostat for Mercedes-Benz Diesel Cooling

The Motorad Standard 251-185 engine coolant thermostat is built for Mercedes-Benz diesel cooling systems that require a 185°F opening temperature. Manufactured to OEM specifications with OE-supplier quality materials, it uses a copper case and wax compound for quick response to coolant temperature changes.

Compatible With Mercedes-Benz E300, S350, 300D, 300SD, 350SD, 350SDL, 300SDL, and 300TD applications that call for a standard 185°F thermostat. The Motorad 251-185 is a direct-fit cooling system service part for OE-specified temperature control.

Key Features

• Standard engine coolant thermostat with 185°F start-to-open temperature
• OEM-quality materials and manufacturing processes
• Copper case and wax compound for responsive temperature regulation
• Jiggle pin weep hole for air relief where applicable
• Offset design with OEM-style seals where applicable
• Bypass dimensions: 1.64 in. diameter and 0.97 in. length
• Sealing flange outside diameter: 2.64 in.; flange thickness: 0.06 in.
• Height: 2.06 in.; height between flanges: 1.44 in.

Detailed Description

Motorad Standard 251-185 is an OE-style engine coolant thermostat engineered for vehicles that specify a 185°F operating threshold. The copper case and wax compound help the thermostat react quickly as coolant temperature rises and falls, supporting stable engine temperature control in demanding cooling systems. This part cross-references NGK 48658 and NTK 25185 for the same application.

Fits 1996-1998 Mercedes-Benz E300, N/A. Fits 1994-1995 Mercedes-Benz S350, N/A. Fits 1991-1993 Mercedes-Benz 300D, N/A. Fits 1987 Mercedes-Benz 300D, N/A. Fits 1992-1993 Mercedes-Benz 300SD, N/A. Fits 1991 Mercedes-Benz 350SD, N/A. Fits 1990-1991 Mercedes-Benz 350SDL, N/A. Fits 1987 Mercedes-Benz 300SDL, N/A. Fits 1987 Mercedes-Benz 300TD, N/A.

Common Cooling System Issues It Addresses

• Engine running cooler or hotter than the OE-specified temperature
• Delayed coolant flow regulation after warm-up
• Temperature fluctuation caused by a worn thermostat element
• Air trapped in the cooling system where a jiggle pin weep hole is required
• Service replacement for Mercedes-Benz diesel thermostat maintenance

Installation Notes and Tips

Verify the OE-specified opening temperature before installation and confirm housing dimensions against the original thermostat. Inspect the sealing surfaces, bypass fitment, and coolant condition during service. Use the correct thermostat orientation for the application, and bleed the cooling system thoroughly after installation to remove trapped air.

Quality Assurance

Motorad manufactures this thermostat to OEM quality materials and safety standards as an OE supplier, using OEM specifications and processes for consistent fit and temperature control.