Another symptom of a faulty thermostat is bizarre sounds. You may hear rumbling, boiling, or knocking coming from the radiator. All these signs point to an issue with your car's cooling system. The thermostat also affects the temperature of air that flows in your vehicle through the vents.
Temperature Fluctuations: One of the most common signs of a bad thermostat is erratic temperature readings on your dashboard gauge. If you notice that the temperature gauge moves from normal to hot quickly or fluctuates unexpectedly, it's a clear indication that your thermostat may be malfunctioning.
The thermostat is a mechanical device that acts to keep water in the engine until it reaches a certain temperature, then the thermostat opens and allows the hot water to flow into the radiator and cooler water to return to the engine from the other end of the radiator.
High temperature readings
The main symptoms of a failing thermostat are related to engine overheating. It can be easily noticed because the temperature gauge in the vehicle will probably read unusually high. This can be caused by the valves being stuck in a closed position.
Sometimes, the problem is not immediately obvious. You might hear a hissing sound or notice a radiator not reaching the desired temperature despite thermostat adjustments. These are clear signs that your TRV might not be functioning correctly and needs attention.
While there is a small chance that there is an issue with the running temperature of your engine, by far the most common issue with trouble code P0128 is a faulty thermostat. The exact location of the thermostat and issues related to a damaged thermostat may vary depending on your vehicle.
This is an easy problem to solve yourself by simply removing the plastic outer casing and, with a very soft brush, delicately brushing off its coil and contact surfaces. It is most effective to clean the thermostat first at its lowest setting, then again at its highest setting.
The primary indicator that your radiator is or has failed is an overheated engine. Many moving parts in your engine operate at high speeds. Heat accumulation results from insufficient cooling, increasing friction. If enough heat is generated, internal components may melt, necessitating the engine replacement.
If you drive with a bad thermostat, your car could overheat, causing severe and expensive engine damage. And while it's technically possible to drive without a thermostat, we don't recommend it. Your car will not reach an acceptable operating temperature, resulting in higher fuel consumption and excessive engine wear.
Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.
If your engine is overheating but the coolant is full, there may be an issue with the radiator or cooling system as a whole. This could be caused by anything from a mechanical fault of the radiator fan to a damaged expansion tank.
Go to the radiator that was quickest to heat up. Close its lockshield valve in a clockwise direction and then open it by one-quarter turn. Measuring the temperature: with the fastest radiator warm, take a couple of temperature readings using your digital thermometer. First, from the pipework next to the valve.
Other than your car consistently running hotter than normal, other signs of a clogged radiator may include radiator hose problems, low coolant levels, rust-colored coolant, and leaking coolant.
If the coolant level is low, add the correct coolant to the reservoir (not the radiator itself). You can use diluted coolant by itself, or a 50/50 mixture of concentrated coolant and distilled water. When coolant rises to the cold fill line, replace cap and tighten it until you feel it click.
Another problem that a carbon dioxide test could possibly reveal is a ruptured cylinder head, which causes similar symptoms to a failed head gasket. In many cases, a cylinder head crack will be too tiny for the human eye to spot, yet it could still be a major problem.
If the coolant level is dropping and there is no external leak evident, then the coolant is probably leaking internally, into the engine. If the car has recently overheated then this could have caused the head gasket to fail. If it has, it could be leaking coolant into the combustion chambers.