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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Re: no hot air from heater, blower runs fine
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.
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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.
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.
get a radiator flush run for about 20 miles .that will clean the radiator core and the heater core. of dirt and rust .then drain and refill with 50/50 mix of anti freeze. then heater on full run the engine with the expansion bottle cap off to bleed the air from the system then refit the cap.
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.
try backflushing the heater core,remove heater coolant hoses and flush both ways with a garden hose,do you have a air compressor ,blow water back through heater core both ways,this asuming that all valves are working allowing coolant to flow and all air doors in car are opening,if so this fix has worked many times for me in older cars note works better to hook water hose to hoses or a short peice of hose on heater core,good luck
CHECK THE HEATER CORE. MORE THAN LIKELY IT IS PLUGGED OR THE HEATER CONTROL VALVE IS NOT FUNCTIONING PROPERLY. THE HEATER CONTROL VALVE CONTROLS THE WATER TO THE HEATER CORE. THUS NO FLOW, NO HEAT. GOOD LUCK.