Located between the engine block and the radiator, the thermostat in an MX5 NB (1998–2000) determines when coolant is allowed to flow through the main cooling circuit. This allows the engine to warm up faster and keeps the operating temperature stable even under varying conditions. When replacing the thermostat, the cooling system gaskets are often checked at the same time, because temperature differences and pressure buildup converge precisely around the thermostat housing. A small leak may seem harmless, but it can ultimately have a major impact on the reliability of the entire cooling system.
