Q: What are the symptoms of a bad coolant temperature sensor

The coolant temperature sensor on this engine sends a feed back voltage data to the computer. The computer uses this data to monitor the engine temperature from about minus 40 degrees F to over 300 degrees F. The coolant sensor may cause the engine to run the cooling fans at the wrong time if sensor is reading too high of temperature output. The engine may run extra rich or lean if the temperature output is not correct. If engine ran too rich you may notice black smoke out of exhaust or lower than expected fuel mileage and possible fouling out of the spark plugs. If engine ran too lean then the engine may have pre ignition and hesitate on acceleration and have less power. The main thing to look for when a coolant sensor is not working correct is the engine temperature is overheating or getting hotter than it normally does. Have the engine checked for overheating. The mechanic can compare the coolant sensor reading with the actual engine temperature using a laser temperature tester and a computer to scan the engine data. If the coolant sensor is not registering correct temperature it should be replaced.