2000 Buick LeSabre Heater

3800 with 172k has begun to lose heater temp. I still have heat, but greatly reduced. Changed out thermostat and topped off anti-freeze, but got no improvement. I'm thinking a back-flush may be in order in an attempt to clear junk in core. If that doesn't do it, how big a deal is it to replace the heater core? Is there anything else that should be checked first? Temp control? How?Thanks.

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On Sat, 27 Oct 2012 15:03:13 -0700 (PDT), dplayer

With that many miles it is possible the heater core is clogged. Back flushing may help, but don't get your hopes up. The passages are pretty small in them. Unlike the cars of yesteryear, it is difficult to get most cores out to replace them.
It is also possible the damper is not closing properly. On mine (2001), one side was hot, the other cold depending of whether you were running heat or AC. I'm not sure how to check it as I gave the car away before it became a problem. Engine still ran well, everything else was going to crap though so it was good riddance and my last ever GM car.
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On Sat, 27 Oct 2012 15:03:13 -0700 (PDT), dplayer
reduced. Changed out thermostat and topped off anti-freeze, but got no improvement. I'm thinking a back-flush may be in order in an attempt to clear junk in core. If that doesn't do it, how big a deal is it to replace the heater core? Is there anything else that should be checked first? Temp control? How?Thanks.
Most likely a mixer door malfunction. Could be as simple as the clip connecting the cable to the door broke. Does the A/C blow cold?
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wrote:

I concur that it's more likely a door issue, particularly if it was sudden onset. Another approach could be to monitor the temperature of the heater core inlet and outlet hoses upon cold startup, with the temperature control set to its hottest position, fan off. If at a fast idle they seem to warm at the same rate, quickly attain the same temperature as one another and then other coolant hoses upon the opening of the thermostat (determinable by the dash temperature gauge or more precisely the upper radiator hose), then flow through the core, and an even less likely case of clogged exterior fins, is probably not the problem.
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I had a 2004 Century 3100 with the dual temp controls, and the passenger side would blow hot all the time no matter what you set the control at for that side. Unacceptable in the summertime. I posted somewhere and got this reply, and it worked:
"This can be caused by either a intermittant feedback error in the actuator itself, an overflexing door or a fault in the control head.
You can attempt a reset procedure. Use the following steps to perform the calibration update: 1. Turn OFF the ignition. 2. Remove the battery positive voltage circuit fuse of the HVAC Control Module. Important: The module memory will not clear if the battery positive voltage circuit fuse is installed in less than 60 seconds.
3. Wait 60 seconds. 4. Install the fuse. The fuse in the in I/P fuse panel and is labeled HVAC. This will sweep the temp and mode doors in an attempt to relearn the positions. Bear in mind if there is a fault in the actuator, controller or related wiring and it cannot relearn the door position it may re-occur."
This solution did work, and eventually the original condition re-occured. Then I performed the above procedure a second time, and haven't had a problem in several years.
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replying to dplayer, trevor wrote: can I unhook heater core and still drive car
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On Thu, 17 Mar 2016 02:18:02 +0000, trevor

Yes, as long as you block the hose ends so it does not leak.
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