The viscosity valve or thermostat operates the oil cooler bypass valve when the oil is cold.

• A. True
• B. False
• C. Only when engine is overcooling
• D. Only in cold weather

Answer: (A)

The main idea here is how oil temperature is controlled in the engine’s lubrication system using a bypass for the oil cooler. A viscosity valve or thermostat acts as a temperature-sensitive switch that governs the oil cooler bypass valve. When the oil is cold, this device keeps the bypass open so the oil flows around the cooler rather than through it. This lets the oil heat up quickly to its operating temperature instead of being cooled down further by the cooler. As the oil reaches the desired temperature, the valve gradually closes the bypass and routes oil through the cooler to regulate and maintain proper temperature. So the statement is correct: the viscosity valve or thermostat operates the oil cooler bypass valve when the oil is cold. The other options aren’t accurate because the system’s purpose is not about overcooling or ambient weather, but about warming the oil efficiently by bypassing the cooler during cold startup and then circulating through the cooler once warm.