🔍 Key Concepts

• the basic function of a thermostatic valve in a diesel engine cooling system • what happens to coolant temperature control if the thermostat sticks open or sticks closed • difference between temperature problems and level/pressure/heater problems in cooling systems

💭 Think About

• Ask yourself: what is the primary job of a thermostatic (thermostat) valve in a cooling system? • If the thermostat fails stuck open or stuck closed, how would that affect the engine’s operating temperature? Too cold? Too hot? • Which answer choices describe a direct effect on temperature control, and which describe secondary or less-related issues like level, pressure, or external heaters?

✅ Before You Answer

• Identify which option is most directly linked to controlling coolant temperature, not just any cooling-system symptom. • Consider both failure modes: thermostat stuck open vs stuck closed—which answer choice would cover either abnormal condition? • Verify that the option you pick could reasonably occur without any changes to tank level or external heater operation.