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1992 brougham
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15 Posts
Discussion Starter #1
I am writing about a heat problem with a 1990 sedan deville 4.5L. I apologize for the length of this message but I am stumped. I bought car last year and it had no heat. The antifreeze was brown and looked nasty. I changed heater core, all heater hoses, thermostat , and radiator cap. I put in fresh antifreeze. At first no heat but then I ran engine without radiator cap and increased idle and I finally got heat. For some reason the next day , no heat. As it was Spring I let it go. I overheated a few months later on a 95 degree day. I replaced the radiator and water pump and flushed system well. This solved the overheating problem but still no heat. I dont think I am getting proper flow thru the heater core even though everything is new in the cooling system. I pulled off cover under dash to expose heater core and it does get hot. There is a water control valve but it looks like a Tee . I think the coolant is mostly bypassing the heater core and going through the other branch of the Tee. The service manual says there is a computer control on this valve but that is impossible as there are no vacuum or electrical connections. I have also been checking controls on the inside of car. The mixer damper at the heater core is moving as it should. There are no error codes on the computer. The only thing I see I dont like is that the AC compressor is on a lot even though I have heat set to 90? I disconnected AC at low pressure switch so it wont run for now, With all this playing around I do have some heat but not much. I want to eliminate cooling system before moving to climate control system. Sorry for such a long book, I cant afford to go to dealer after all this, Please help
 

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02 eldo collectors series, 98 eldo, 97 deville, 96+94 SLS,
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219 Posts
Did you check the whole heater core to see if its hot, when you had the cover off and the core exposed? I just discovered today that you can have hot hoses but still have a clogged heater core, check to see if the bottom of the core is cold when the car is warmed up and the heat is turned on.

Jack
 

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2005 CTS-V, 1994 Infiniti Q45
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7,658 Posts
Well he said he replaced the heater core, so Im gonna rule that one out.......

Do you have the FSM?? In the words of Ferris Bueller "If you have the means, I highly recommend picking one up".......

There should be a procedure to force the heater core valve all the way open.......
 

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1992 brougham
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15 Posts
Discussion Starter #5
I dont remember part of heater core being cold, I had run the car for a long time and it seemed like the whole thing was hot? I will check again. I did buy the factory service manual but all it says is to check inlet and outlet hose to core and outlet should be a little cooler than inlet, mine seems too cool. I remember the one day heat work both hoses were nice and hot. the heater core is new I dont see how it could get plugged right away, could there be air in the core? I did swap out this water valve with one from my parts car but no difference, there is mention in FSM about controlling this water valve but I do not see it being possible, I dont know if there are errors in these books? keep trying I appreciate the suggestions.

Steve
 

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02 eldo collectors series, 98 eldo, 97 deville, 96+94 SLS,
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219 Posts
Like ELwesso said, its probably not your heater core, if you replaced it, but air is unlikely, if you think it is air, then get the car warmed up then just releive the pressure by opening the radiator cap a little, and hold it down so it doesnt blow off on you, then once the pressure is relieved, while the car is running take off the cap, kick up the idle so the coolant level drops and top off the coolant, then re apply the cap and let the idle down, that will pressurize the system, then later on check the coolant level again, cause if there is any air in the system it will get pushed out through the overflow tube. That whole heater valve thing has got me confused, because #1 I have never seen one go bad on a deville and I have owned my 90 since 92 and its got 198,000 miles on, and #2, how could there be one inside that "T" if there are no vacuum lines and no electrical connectors? Something has to control it, I think if it ever seems to go bad and you change it and it works, its probably just clogged, but as I said, I never had to change one, and I have owned 9 Caddys. If the core is nice and hot I would say you either have a bad climate control unit, (the display on the dash) or your mix door isnt opening, there is only 1 mix door to control the flow of heat into the heater box, the other vacuum controled doors are just for switching from defrost and A/C. Thats all I can think of for now, check it out again and let me know what you come up with.

Good luck, Jack
 

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1992 brougham
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15 Posts
Discussion Starter #7
thanks to all for their input, this forum site is great! I goofed on this one, when I originally changed heater core and flushed system I wasnt thinking too straight. I must have flushed some crud from the passages in the engine right into the new heater core. I replaced core again yesterday and cut open old core. there was a ton of brown crud that actually hardened. The new core is great! plenty of heat now. Thanks to alll.
 
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