A defective thermostat can result in engine overheating and potential internal damage. Improve the reliability of your 6.4L cooling system with the Mishimoto Ford 6.4L Powerstroke High - Temperature Thermostats These thermostats are designed as a direct - fit replacement for your aged factory units. The Mishimoto thermostats have a higher activation temperature (198 F208 F) compared to the factory thermostats (192 F203 F). The higher activation temperatures restrict coolant flow longer to allow a quicker engine warm - up, making these thermostats ideal for use in cold climates. Pair this thermostat set with the Mishimoto 6.4L Powerstroke Aluminum Performance Radiator for a complete cooling system overhaul. As with all our products, these thermostats include the Mishimoto Lifetime Warranty, ensuring superior product quality and craftsmanship.