heater only works under throttle?
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, heater only works under throttle? in Past Cadillac Vehicle Discussion; Ok, as it goes the heater decided to go on the fritz as soon as the snow starts flying around....my ...
  1. #1
    CadillacJack219 is offline Cadillac Owners Member
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    heater only works under throttle?

    Ok, as it goes the heater decided to go on the fritz as soon as the snow starts flying around....my car is a 1990 brougham 5.7.... I have no idea what happened, it could be sheer coincidence but it seemed to be working up to the point where I changed the lower rad hose. I wasn't driving the car a lot then and it wasn't really cold enough for me to notice. I am pretty warm blooded so I don't really kick on the heat untill its below 50 outside. The screwey thing is that it only works around or above 2k rpm. At that point the air is only "warm" not the blast furnace that it usually is. Let off the throttle and shortly after the air dwindles to cold. I figured the culprit was air in the system so I checked, double checked and triple checked with no avail. I even parked it on the steepest hill I could find trying to coax any air out, maybe got a pint of coolant in at that point.... that may sound stupid but I'm shooting blind here. A friend said it could be a vapor lock and to run it full tilt up and down the road and see if that helps, I'm doubtful of this but I'm not rulling out trying it as a possible last resort. The thermostat is gutted but it has been since I got the car, it was an emergency roadside fix. It never hurt anything so I left it be, nothing could of changed there? I remember a few years back that a neighbor was having issues and it turned out to be vacuum related. The only two vaccum lines that run into the firewall are black 1/8" plastic lines, both are intact to the point of the firewall anyhow. What should I be looking for.... I'm really hoping this isn't a "dashboard removal" job but so be it if it is. Any direction I should look here?

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  3. #2
    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    A gutted thermostat causes over cooling and little to no heat. It would be a waste of time to look for other possible problems without replacing it first.

  4. #3
    cadillac kevin's Avatar
    cadillac kevin is online now Cadillac Owners Master
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    I vote for thermostat as well. Its cheap, easy, and would cause a "no heat" condition

  5. #4
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: heater only works under throttle?

    The thermostat should always be changed whenever the coolant is drained. Cheap insurance.

    Anyone over the age of 30 who has enough automotive experience to help will have a difficult time reading your post as displayed.

  6. #5
    carnut is offline Cadillac Owners Master
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    Re: heater only works under throttle?

    Replace thermostat. should be a 195 degree one first. THEN, post back. This system is fully automatic if you allow it to be! Set the temp to 75 or so, button in auto and leave it alone except to use defrost as needed. Using it as a manual heater/ A/C system puts undue wear on vacuum pots and electric components. This car is not prone to air in the system.

  7. #6
    CadillacJack219 is offline Cadillac Owners Member
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    Re: heater only works under throttle?

    Yea I was kinda figuring I had something to to with the demise of it.... I'm going to advanced auto later so ill pick one up and let y'all know what happens. Sorry about the way that posted Ape, my computer fried in the last storm so I'm doin this on a cell phone (total pita). I can hardly figure out how to text on this thing, let alone try to use the internet lol.

  8. #7
    Jeff R's Avatar
    Jeff R is online now Cadillac Owners Fanatic
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    Re: heater only works under throttle?

    I'm sure you will guess I will say replace the thermostat too. But that being said, it did work before without the t-stat so something has changed. The faster the engine turns, the faster the water pump turns and more pressure. I'm not sure of the configuration but without the t-stat being closed, there is nothing to force the water into the heater core--the water probably just goes back into the upper radiator hose and not into the heater core unless the engine is turning so fast that it just overflows back to the heater core. See if both heater hoses are the same temp. If not then there is a blockage or air in the system. I had this with my Impala a few years ago. Since you drained the system you could have air in there. Take the heater line off and hold it up in the air. Stick a funnel on it and fill with coolant so that you know the line is full and then reinstall it. See what happens then.
    Jeff

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    The Ape Man's Avatar
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    Re: heater only works under throttle?

    Quote Originally Posted by CadillacJack219 View Post
    Yea I was kinda figuring I had something to to with the demise of it.... I'm going to advanced auto later so ill pick one up and let y'all know what happens. Sorry about the way that posted Ape, my computer fried in the last storm so I'm doin this on a cell phone (total pita). I can hardly figure out how to text on this thing, let alone try to use the internet lol.
    NP. I despise my cell phone. Totally useless on the internetz. Best of luck.

  10. #9
    CadillacJack219 is offline Cadillac Owners Member
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    Re: heater only works under throttle?

    Well I changed the thermostat and the problem got worse, now you really have to hold the rpms to get any kind of warmth out of the vents. The other thing I noticed is the engine temp light is now lit, very faint but its trying to come on. Water pump possibly?..... so lost

  11. #10
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    Re: heater only works under throttle?

    You car has symptoms that your heater core is plugged. Pull off the lines going to the heater core and flush them. Buy a hose adapter at HD to connect a garden hose.

    Tom C.

  12. #11
    CadillacJack219 is offline Cadillac Owners Member
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    Re: heater only works under throttle?

    Ill give it a shot this weekend Tom, also I was thinking on draining the coolant and then flushing the whole system with vinager and water. Did it on a little toyota a few year back, all kinds of nasty stuff came out..... I'm just not sure if it can hurt anything doing that, only tryed it that one time.

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