Bad Thermostat Symptoms: Overheating or Running Cold

The thermostat is a small, inexpensive part, but when it fails it can cause big problems, including overheating.

What the thermostat does

The thermostat is a valve between the engine and the radiator. When the engine is cold, it stays closed so the engine warms up quickly. Once the engine reaches operating temperature, it opens to let coolant flow to the radiator and keep the temperature steady.

Stuck closed

If the thermostat sticks closed, coolant can't reach the radiator. Symptoms include:

• Rapid overheating, sometimes within minutes

• Temperature gauge climbing into the red

• Upper radiator hose hot while the lower hose stays cool

This is the dangerous failure. Stop driving to avoid engine damage.

Stuck open

If it sticks open, coolant flows to the radiator all the time, so the engine takes much longer to warm up or never reaches full temperature. Symptoms include:

• Temperature gauge staying low

• Worse fuel economy

• Check engine light, often with code P0128 (coolant temperature below thermostat regulating temperature)

• Weak heater output (less noticeable in Jamaica, but still a sign)

Other signs

• Temperature gauge going up and down erratically

• Coolant leaking around the thermostat housing

Replacement

Thermostats are often replaced when the coolant is changed or during cooling system repairs. Always use the correct temperature rating for your engine, and bleed air from the cooling system after the job.

Don't remove it

Some people remove the thermostat to stop overheating. This causes the engine to run cold, increases wear and fuel use, and can trigger warning lights. Replace it instead.

Need help with this? RCJ Mobile Mechanics comes to you in Portmore, Spanish Town, Kingston, St. Andrew and across St. Catherine. Call or WhatsApp (658) 207-6565 or book a mechanic online.