Cooling system

Did you make sure the coolant level is full? I do not see how the heat would have stopped working from that. The nipple comes from behind the thermostat right off the water pump to feed the heater core coolant.

Hi guys. Allow me to add one tidbit for thought. New radiators usually come with plastic caps on the hose connections. Often those plugs are painted black when the radiators are painted. I saw these same symptoms happen to a coworker who overlooked those plugs when he connected the hoses. This sounds stupid, but it can happen to the best of us.

The clue to this is no coolant will come out when the bleeder screw is opened or a sensor near the thermostat housing is removed.

If you have the Saturn Sl1 they do not get air pockets when you change radiators etc I have never seen one do that.I have worked on them for over twenty four years. What brand thermostat did you buy? Maybe you got a bad thermostat and it will not open?Also, I have never seen a water pump on those cars stop moving coolant. Unless the water pump literally came apart and you would know if that happened.

The car overheating a bad radiator cap or blown head head gasket. Also, is your coolant temperature sensor good? They fail often on those cars. I would replace the cap with a Stant one. I always buy Stant radiator caps and thermostat. Why don't you replace the cap with a Stant exchange the thermostat for a Stant one and see where your at then.

Okay, let me interrupt again with another comment of value. A lot of original thermostats have a tiny bleed hole with a little dangle hanging in it. That is to allow the hot coolant to migrate over to the thermostat so it will open. On some engines the thermostat is a good distance from where the heat is being generated, and the temperature sensor for the gauge is closer to that heat source. Two clues are the thermostat will open if you allow the engine to run long enough at the excessively high temperature, and it will usually open if you run the engine then stop it when it gets too hot, and do that multiple times.

The more common symptom is the gauge goes higher than normal, then suddenly drops to too cold, then repeats four or five times before stabilizing. The high temperature is detected by the gauge's temperature sensor, but it takes about another twenty seconds for it to reach the thermostat, causing it to open. When it opens, coolant starts to circulate, and the cold coolant from the radiator rushes in and causes the thermostat to close again. This happened on my 1988 Grand Caravan, but the funny thing is it did not start doing that until over a year after the thermostat was replaced. The fix was to drill a 1/16" bleed hole in the thermostat.