The function of the Isuzu Thermostats is to control the flow of coolant out of the engine. The thermostat can accomplish this task because of the bi-metal spring in its makeup. The opening and closing of this spring are predetermined by the temperatures of your Isuzu engine so it can warm up faster and provide heat in the winter sooner.
Connected to the spring in the thermostat is a valve. It is this valve in the engine that prevents or permits the flow of coolant out of the Isuzu engine block. In rare instances, this valve becomes stuck in the open or closed position. In either situation, the Isuzu thermostat should be replaced so the engine can function as it was designed too.
The problem when a thermostat is stuck in the open position is the flow of coolant out of the engine is uncontrolled on a continuous basis. Because of this the optimum operating temperature of the engine can not be reached or maintained. The performance and mileage of the Isuzu engine is then compromised until this condition is changed and a new part is installed on your engine.
If the thermostat is stuck in the closed position, no coolant is permitted to flow out of the engine block. When this is the situation on your vehicle, the engine will overheat is a very short allotment of time once it is started. To fix this condition for the short term requires gaining access to the top of this temperature control device by removing the upper radiator hose on its housing unit and punching a screwdriver through it. This will permit the coolant to flow again until a new component can be installed in your vehicle.