Although the humble thermostat isn't generally considered to be a "high-tech" component, it continues to serve a number of very critical functions in the modern, computer-controlled import vehicle. To better understand these functions, let's first consider that carbon and water are two major by-products of internal combustion that accumulate in an engine's motor oil. Unfortunately, carbon and water combine with motor oil to form sludge inside the engine. This sludge not only gums up and corrodes piston rings, valve guides and hydraulic lash adjusters; but it also clogs oil pump screens and other internal lubrication passages in the engine, not to mention blocking the holes that drain oil from the cylinder head and engine block into the oil pan. Eventually, even a low-mileage engine can be destroyed by sludge accumulation caused by an inoperative thermostat.

CRANKCASE VENTILATION

Early in the 20th century, auto manufacturers realized that the only way to control sludge was to remove water from the crankcase oil. Because oil temperatures remain low during short-trip and low-speed driving, water condensation accumulates in the engine oil. Pioneer engine designers began to realize that the only way to remove water from the crankcase oil was to raise engine-operating temperatures close to the boiling point of water. To accomplish this, engineers designed a thermostatically controlled valve (the modern thermostat) to bloc...