Calorstat THF1538.91 Engine Coolant Thermostat

Engine Coolant Thermostat for Ford and Lincoln

Calorstat THF1538.91 is a standard engine coolant thermostat built for temperature control in a wide range of Ford, Lincoln, Mercury, and select Volkswagen applications. It opens at 91 C / 196 F to help regulate coolant flow and maintain stable operating temperature in daily driving and towing conditions.

• Standard engine coolant thermostat for OE-style thermal control
• Opening temperature: 91 C / 196 F
• Sealing flange outside diameter: 2.1
• Height between flanges: 1.38
• Cross-references Motorad 2028-195 and Stant 45399 for the same application
• Part number: THF1538.91

Fitment and application details

This thermostat is used in many Ford F-150, F-250 Super Duty, F-350 Super Duty, Expedition, Explorer, Mustang, and Econoline applications, along with Lincoln Navigator, Mark LT, and Town Car models. It also covers select Mercury Grand Marquis, Mountaineer, and Crown Victoria vehicles, plus 2005-2006 Volkswagen Jetta applications listed in the fitment data. Fits 1992-2022 Ford, Lincoln, Mercury, and Volkswagen models shown in the application list, with position noted as N/A.

THF1538.91 is a direct-fit cooling system service part for vehicles that rely on a 91 C thermostat to manage warm-up and operating temperature. The listed dimensions help confirm housing fit and sealing surface compatibility during replacement. Use this part when servicing a Ford F-150 thermostat, Ford F-250 Super Duty thermostat, or Lincoln Navigator thermostat application that matches the cataloged fitment.

Common issues this part can address

• Engine running cooler or hotter than expected
• Slow warm-up after cold starts
• Temperature fluctuation during stop-and-go driving
• Cooling system service on a Ford F-150, F-250 Super Duty, or Expedition
• Replacement of a worn thermostat in Lincoln and Mercury cooling systems

Installation notes and tips

Verify the thermostat housing style, sealing flange diameter, and height between flanges before installation. Drain coolant as needed, clean the mating surfaces, and inspect the housing and gasket sealing area for corrosion or debris. Confirm the 91 C / 196 F opening temperature matches the original specification for the vehicle before reassembly.

Quality assurance

Calorstat supplies cooling system components for service applications that require accurate temperature control and consistent fitment. This part number, THF1538.91, is cataloged with direct interchange references and vehicle-specific application data to support confident selection.