Which symptom is most closely associated with a defective thermostat in the cooling system?

Which symptom is most closely associated with a defective thermostat in the cooling system?

• A. Overheating at high speed
• B. Radiator hose collapse as the engine cools
• C. Rapid coolant loss
• D. Engine misfire

Answer: (B)

The thermostat’s job is to regulate coolant flow between the engine and the radiator so the engine stays at the right temperature. If the thermostat is defective and won’t open properly, coolant can’t circulate to the radiator when the engine is hot. That causes the cooling system to operate under abnormal pressure while hot, and as the engine cools the coolant contracts, creating a vacuum in the closed system. Without a venting path, this vacuum can pull on the upper radiator hose, causing it to collapse. This hose collapse as the engine cools is a telltale sign that the thermostat isn’t allowing normal flow to regulate temperature. Overheating at high speed can occur with a stuck-closed thermostat, but the collapsed hose during cooling more directly reflects the flow restriction and vacuum dynamics caused by a faulty thermostat. Rapid coolant loss points to leaks or other issues, and engine misfire isn’t a typical symptom of a thermostat problem.

The thermostat’s job is to regulate coolant flow between the engine and the radiator so the engine stays at the right temperature. If the thermostat is defective and won’t open properly, coolant can’t circulate to the radiator when the engine is hot. That causes the cooling system to operate under abnormal pressure while hot, and as the engine cools the coolant contracts, creating a vacuum in the closed system. Without a venting path, this vacuum can pull on the upper radiator hose, causing it to collapse. This hose collapse as the engine cools is a telltale sign that the thermostat isn’t allowing normal flow to regulate temperature.

Overheating at high speed can occur with a stuck-closed thermostat, but the collapsed hose during cooling more directly reflects the flow restriction and vacuum dynamics caused by a faulty thermostat. Rapid coolant loss points to leaks or other issues, and engine misfire isn’t a typical symptom of a thermostat problem.