Cadillac Repair: 2000 Cadi Deville, head gasket problem, upper radiator hose

Question
I recently purchased this car and the " check coolant level " light came on. I filled the overflow resevoir and the engine still got warm, there was no sign of water on the dip stick, so how do you tell if the thermostat is stuck or the head gasket is blown?

Answer
Hi Mike,

     Usually when you get that message it means that the coolant level in the overflow bottle is low or the sensor is defective. Since you added coolant to the full mark and the message is still on I would be looking at the sensor to see if it is a wireing problem or just needs to be replaced.

    As for the car gets warm statement. If you mean that the temperature gauge never really reaches operateing temperature and the air out the ducts is just warm instead of hot then yes the thermostat would be the logical thing to change right after you have determined that the coolant level is full in the radiator which you have already done.

    A sure indicator that the thermostat is stuck open would be to idle the engine say for 10 minuits in park and feel that the upper radiator hose gets warm or hot. Also the heater hoses should feel about the same temperature as the upper radiator hose or hotter. Then go for a drive at 45mph or faster and the longer you drive the cooler the air temp. gets. At that point I would be comfortable saying the thermostat is partially stuck open or opening too soon.

    If on the otherhand 2-3 minuits after the engine has been idleing with the radiator cap off coolant starts to come bubbleing or spraying out then that could be a head gasket sign. Another indicator would be as you are driveing the air temperature from the ducts is hot and then 5 minuits later it goes cold momentarily and the shoots up to overheating and then back to normal or cold. Then I would be looking at a possable head gasket problem.

     Hopefully that answers your questions. Bill