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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92 deville no heat at idle when driving I have some,

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.
2nd , is the blower motor actually blowing,
Traveling down the road causes ram air to push through the heater as long as the controls are set for fresh air intake.
Remember If allumaseal will not plug a leak then more professional measures must be used. Many radiator stop leaks are so effective like bars leak the stuff that looks like rabbit feed pellets that when used professional help must be found because the radiator no longer has the circulation ability to cool the engine and if a vehicle is run any at all above max operating temperatures it will normally result in costly repairs. I have personally used fine ground black pepper and had good results but it must be very fine ground no matter what is used it must be small enough to travel through the small tubes of the radiator and or heater core. If larger particles are used coolant flow will probably be restricted enough to cause either no heat in the cabin or overheating of the engine which most certainly can cause serious damage the very first time.

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Heater core plug how to flush it grand am 1998

The core may be plugged, or it may have an air lock, or the core may be fine and the doors in the heater case may not be opening properly to pass heat.

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.
Good luck.

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disconnect the heat hoses going into fire wall , put hose into one with pressure and flush as it sounds like it could be bloked in the heater core,the other thing that could be the problem be the hot ,cold switch as it restricts the flow to makes the heater hoter or colder , it might need tlc or replacing as it is manaul not elec

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My cadillac is not giving me any hot air ,ive replaced the radiator, changed the thermostat, has a new water pump, where do istart to look.

Feel the 2 tubes at the firewall for the heater core. If they are not getting hot, the heater core needs to be flushed out or replaced. I had this problem with a 1990 Cadilac Deville, it was just a plugged up heater core.

Remember to install sealant after flushing out the system to prevent leaks.

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I have a 1990 subaru loyal, it runs fine but there is a problem with the heat. the heat coming from the heater core isnt very hot, its barely warm. the car gets up to running temp and doesnt overheat. when...

A clog can cause low heater perforance in the winter. I had a 1990 Cadillac Deville that had cold air blowing in the middle of winter, and had the system flushed and that solved the problem.

One can feel the two heater tubes at the firewall leading to the heater core to verify whether or not the antifreeze/coolant is getting hot at the heater core.

Good luck on this repair.

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Did you mean the only time it blows hot air is under acceleration?

First thing check the coolant level in the radiator. If coolant is low the first hing to stop working is the heat.

If the coolant level is fine but the coolant is muddy I woulds suspect a plugged heater core. You can try back flushing it by removing both heater hoses (engine cold) and then use a garden hose to flush clean water through the heater core. Do this on both pipes going into the heater core. Keep flushing until the water runs clear. Re attache the the hoses, remove the radiator cap, start the engine, let the engine come up to temp and top off the radiator with straight coolant (to comp for the water in the heater core). You may have to repeat this process several times over several days but you should be able to get it cleared enough to get sufficient heat without having to replace it.

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What does a heater core do?

The heater core runs off of the cooling system, it is a small "radiator" behind the dash that sits in a box. when the heater core is full of hot coolant, it gives off heat and the blower motor pushes the hot air to the vents.

If a heater core ruptures, becomes clogged with parasites, or gets blocked in a hose (the 2 leading to the firewall under the hood on the passenger side) it causes the car to overheat, and/or leak.

my suggestion is to have the system pressure tested, and flushed if it checks out OK

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