Calorstat TH5699.80J Engine Coolant Thermostat

Engine Coolant Thermostat for Mercedes-Benz

Calorstat TH5699.80J is a standard engine coolant thermostat built for precise coolant flow control in select Mercedes-Benz diesel applications. It includes a gasket and seal, plus a jiggle pin weep hole for easier air bleeding during service.

• Standard engine coolant thermostat
• Start to open temperature: 176.0°F
• Gasket or seal included: Yes
• Seal type: Gasket with rubber seal material
• Jiggle pin weep hole: Yes
• Locating lug for correct positioning
• By-pass valve diameter: 42.0
• Valve-seat diameter: 66.6
• Sealing flange outside diameter: 2.62
• Height between flanges: 1.2

Fitment Details

Compatible with Mercedes-Benz diesel models listed below. Fits 1998-1999 Mercedes-Benz E300, N/A. Fits 1994-1995 Mercedes-Benz S350, N/A. Fits 1990-1993 Mercedes-Benz 300D, N/A. Fits 1992-1993 Mercedes-Benz 300SD, N/A.

This part cross-references Motorad 251-180 for the same application.

How This Thermostat Works

TH5699.80J regulates coolant temperature by opening at 176°F, helping the engine reach and maintain operating temperature. That temperature control supports stable warm-up, consistent heater performance, and proper cooling-system circulation in Mercedes-Benz E300, S350, 300D, and 300SD diesel platforms. The locating lug helps align the thermostat during installation, while the jiggle pin weep hole assists with trapped-air release.

Common Reasons to Replace

• Engine runs too cool or takes too long to warm up
• Temperature gauge fluctuates during driving
• Coolant flow is restricted by a sticking thermostat
• Heater output is inconsistent after coolant service
• Cooling-system service reveals a worn gasket or seal

Installation Notes

Verify housing condition and clean the sealing surfaces before installation. Use the included gasket/seal and align the locating lug correctly so the thermostat seats fully. After installation, refill and bleed the cooling system according to the vehicle service procedure to remove trapped air.

Quality Assurance

Calorstat TH5699.80J is an OE-style thermostat for the listed Mercedes-Benz applications. Vernet is an OE supplier to Mercedes, and this part is built to match the specified temperature and dimensional requirements for service replacement.