Thermostats & Accessories
Why Marine Engine Thermostats Matter
Thermostats are one of the most critical — and most underappreciated — components in any marine engine's cooling system. A thermostat regulates the temperature of the water used for engine cooling and keeps pressure in the cooling system to facilitate heat transfer from the heads and the cylinder walls. Without a properly functioning thermostat, your engine is left vulnerable to the two biggest threats to its longevity: overheating and running too cool.
Marine thermostats are subject to constant temperature changes, corrosion, and water pressure, along with mud, sand, and salt — yet they're expected to perform reliably trip after trip, season after season. Today's emission regulations make the thermostat even more important for correct engine operation, and depending on how regulations are interpreted, running without one — or substituting one with a different rating — may put you in violation.
How a Marine Thermostat Works
Thermostats are designed to open gradually as the coolant or raw water in the engine block heats up, allowing hot coolant to pass through the heat exchanger in indirect-cooled engines, or for raw water to pass through the engine in direct-cooled engines and out the exhaust. If the thermostat does not open, the engine will overheat, causing a temperature alarm to sound and risking engine seizure.
A thermostat also provides water pressure for the block, which is another reason never to leave one out of your engine. As a rule of thumb, thermostats can be damaged by very high temperatures, and replacing them after an engine overheat is recommended.
Thermostats & Accessories: What's in This Category
You can choose from thermostats designed to keep your engine operating in the exact temperature range you need, as well as thermostat parts and accessories like gaskets and housings, and thermostat kits that come with everything you need to make a complete replacement. Whether you're maintaining an outboard, stern drive, or inboard powerplant, having the right thermostat — and the right gaskets and housing components to seal it properly — is essential for a leak-free, correctly pressurized cooling system.
At the specified maintenance intervals, the thermostat should be examined for corrosion, sticking, and for proper temperature regulation. In saltwater or muddy water operation, more frequent inspections may be required.
Top Brands in Marine Thermostats & Accessories
Coleman is a trusted name in the marine space, known for building durable, reliable powersports and marine products engineered to handle demanding conditions. Coleman's thermostat-controlled water cooling systems are designed to maintain optimal temperature for reliable performance, making their thermostat components a popular choice for boaters who want confidence in their engine's thermal management.
Robertshaw brings decades of precision temperature-control engineering to the marine world. Long recognized for their expertise in thermostatic components across multiple industries, Robertshaw thermostats are valued by marine mechanics and DIY boaters alike for their consistent calibration and durability in harsh marine environments.
Shopping Tips for Marine Thermostats
- Match the temperature rating: Marine thermostats are rated by their opening temperature (commonly 143°F, 160°F, or 180°F). Always consult your engine's service manual for the correct specification.
- Replace the gasket too: When installing a new thermostat, always replace the housing gasket to prevent coolant leaks.
- Consider a kit: Thermostat kits bundle the thermostat, gasket, and sometimes the housing together, streamlining the replacement process.
- Inspect after overheating: If your engine has experienced an overheat event, replace the thermostat as part of your diagnosis and repair — it may have been permanently damaged.