Question about 1994 Cadillac DeVille

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No hot air from heater, blower runs fine

1990 Cadiallac Deville has no heat coming out. Had radiator and heater core flushed by professional and he said all looks good but no heat. Controls appear to be working because it changes from heat to air and all flappers are working. Could water pump be weak not allowing enough water flow through the heater core?

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  • stationman56 Jan 21, 2009

    Thank you for your response. The water pump appears to be OK because the engine does not overheat, there is no water leaking out and with the radiator cap removed and the thermostat open I can see the water circulating. I feel, based on your comment about the heater core that I have poor circulation through the heater core due to it being partially blocked. I am going to replace the heater core and see if that cures the heating problem. The car has 140,000 on it and based on the junk the mechanic got out when he flushed it, I assume the heater core needs replacing. The coolant the mechanic pulled out was also dirty and rusty.

  • Anonymous Mar 16, 2014

    heater core went out I bi passed it. now the car's information center is saying ac/hot when it begans to idle off

  • Anonymous Mar 16, 2014

    my heater core went out ant ever since I ve been having problems with my cooling system. my fans use to come on only when the air is on but now they are not coming on. what else besides the fans can cause the car to overheat

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The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.

Since you state the 2 things you ruled out, that leaves only the water pump. Is the car running hot? The thermostat may be sticking as well... but im leaning toward the pump.

Posted on Jan 21, 2009

  • Christopher scroggins
    Christopher scroggins Jan 10, 2014

    waterpump been replaced within 2 months

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If you have no problems with any valve or perhaps the heater blower motor then heater core could be plugged, I have back flushed some successfully by changing the flow of coolant backward and catching back flow in a separate container. Could actually see large amounts of coolant stop leak.
1st thing to check, is coolant level full.
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Traveling down the road causes ram air to push through the heater as long as the controls are set for fresh air intake.
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With the engine at normal operating temperature, feel both the inlet and outlet core hoses at the firewall. If the coolant is circulating both hoses should be hot. If only one is hot, try cracking open the outlet line, with engine running, to get flow started from an air block. (The outlet line will run from the firewall to the front of engine near or at the water pump housing. The inlet for the heater comes off the top of engine from a head fitting and goes to the firewall.) If no flow results, the core may be plugged. To flush the core, take both hoses off at the firewall or off at where they fit on the engine, and put a garden hose into the outlet-flush it backwards-run until clear-let the water run to ground or use a catch can if able to. Some people use compressed air into the core instead of water flushing. Either way, you should see some sediment come out if it had any blockage. Once you get the heater core circulating, any further heater problems need to be addressed at the heater case. Make sure the temperature blend door can open and close-this door opens to let blower fan air pass across the heater core.
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