1996 Ford Ranger thermostat

Leaving the thermostat out entirely reduces the pressure that your cooling system operates at. This decreases the temperature at which the coolant boils and can cause bubbles of air in the coolant at the hottest places in the engine. These bubbles then act as a thermal insulator which makes those hot parts of the engine even hotter. But your temperature guage will still be showing 'normal' temperatures. If the engine runs hot in one particular area, it can damage the piston rings eventually causing the car to smoke, burn oil, and eventually cause total engine failure.

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