Cadillac Repair: 97 Deville Concours Overheats Intermittently, coolant temperature sensor, head gasket problem

Question
Two weeks ago, my car overheated where message center said stop engine.  Added coolant next day, was ok until rpm's went over 2500 for 5 - 10 minutes.  I drove it for 5 hours the next day, just kept the speed under 2300 rpm.  The Cadillac mechanic did the dye test for exhaust gases in the radiator - no change in color.  He said the heater core had a leak and thought it was the head gasket anyway.  I have plenty of heat when needed, but use about 2 quarts of coolant a day.  I can drive at 2300 rpm - 68mph and all is fine, but when I slow to 45 mph, the gauge starts to creep to 2:00.  I did add some Bars-Leak, but nothing changed.  Any suggestions, Thanks.

Answer
Hi John,

      2 quarts a day is kind of alot. Enough that you should be able to see something on the ground or in the cylinders. What I would do is run the engine in the shop or in your case at your mechanics and let it warm up until the thermostat opens. Shut the engine off and make sure the antifreeze level is at the full mark. Then install a special coolant pressure gauge that uses air pressure from the airline so it will have a constant 15psi all the time. After the engine has cooled off remove the tester and see where the coolant level is. By this time you might see antifreeze on the ground and be able to follow the trail to where it is comming from. If there still is no signs of external leaking then remove all the spark plugs and useing a flashlight look into the cylinders to see if any is inside. You very well could have the start of a head gasket problem or a head bolt that the threads have pulled out of the block.

     As for the temperature, it is normal to see the gauge go up to 226 degrees or so but if 230 or higher then there is a problem. There is a possability that the coolant temperature sensor might be out of calibration and reading a higher temperature that it really is. Useing an infra red thermometer is the best way to tell its accuracy.

     Let me know if I can be anymore help. Bill