Cadillac Repair: 1990 Sedan DeVille/Cold Engine, heater hoses, floor ducts

Question
When the temperatures dropped this winter, my engine became very slow to warm up, which causes the engine to rev high before shifting.  It does not seem to want to warm up as all, as the heater does not blow warm air.  I replaced the thermostat, but this did not help.  Any suggestions would be very welcome.

Answer
Hi Todd,

      Looks like you did the first thing I would have suggested and that is to replace the thermostat. I will assume that you have checked the antifreeze level in the radiator to find that it is up at the top. If it is low aprox. 4" or more then that will not allow hot coolant to flow through the heater core. Also I will assume that the airflow from the vents or floor ducts is strong but just not hot correct?

        Since you have an older car 2 things that can happen is the heater core can plug up inside and need to get flushed out or replaced. What I do is warm the engine up until the thermostat opens and then feel the temperature of the upper rad. hose. It should be almost too hot to hold onto. Now go to the 2 heater core hoses that are under the plastic panel on the passenger side under the hood. Feel both of those hoses. If the hot water valve...I don't remember if it was still in use on the '90 or eliminated shortly thereafter...is allowing coolant to flow through it and one heater hose is hot and the other almost hot then the core should be ok inside. If only 1 heater hose is hot and the other is only warm then the heater hoses need to be removed and the core flushed out in both directions. If flushing doesn't help then replaceing the core will hopefully get the heat back.

      The other thing that usually happens is the programmer motor gears wear out allowing the hot/cold door to stay in one position...in this case more to the cold setting. To see if that is the problem remove the screws that hold the glovebox and then remove the glovebox. In behind you will see the programmer that has a rod on top and attaches to the hot cold door which changes the temps. What I do is to warm the engine up until the thermostat opens and set the temp to 90 and watch it go all the way to one direction. Then litely grasp the rod and set the temp to 60 and see if there is any skipping feel in the rod as it slides through your finger and thumb. Do this several times to check for skipping because it might work ok in one direction but skip going the other way. The rod can also be removed and manually moved in each direction to check for hot or cold. Then to adjust it set the temp to 60 or 90 and pull the rod all the way to that side and snap it in place.

      There is the possability that the thermostat is opening too soon but I would suspect the heater core or programmer motor to be the problem.

      Let me know if you need anymore help. Bill