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Hey at least it ain't politics !
Our '99 Toyota 4Runner has a heater problem that's driving me (more) nuts . The heater apparently isn't getting enough coolant flow , and isn't putting out enough heat . I've checked all the hoses from the motor thru the valve and heater core and back to the engine , hoses are OK and the core isn't plugged . I've also flushed the entire system , all hoses and the core and associated plumbing . After flushing it out it'll do OK for a short time then it's back to not enough heat . Pertinent info - the water control valve is cable operated from the dash along with the gating for airflow in the heater box . I don't think there's a t-stat type device in there for temp control , but if there is one and it's malfing that might explain it . The coolant level is up , and circulating when observed in the radiator . This has really got me stumped , and the wife is getting pretty hot herself about it - we're getting into the cold season here and she's the main driver . -- Snag
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On Friday, October 30, 2015 at 8:51:17 AM UTC-4, Terry Coombs wrote:

Does the car have a temp gauge? Any chance the problem is the engine is running cold due to a bad thermostat?
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On 10/30/2015 8:58 AM, trader_4 wrote:

Quit reading my mind!
BTW, all those images of naked women ren't really there.
--
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Christopher A. Young
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trader_4 wrote:

Not a chance , the motor temp is where it shouild be - and it does work well for a short time after flushing .
--
Snag



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On 10/30/2015 10:17 AM, Terry Coombs wrote:

Strike that one off the list of possible problems.
--
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Christopher A. Young
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On Friday, October 30, 2015 at 8:51:17 AM UTC-4, Terry Coombs wrote:

Are you sure that the blend doors are opening and closing properly?
I've had them fail on various model cars. Until recently I had a 2002 Mitsubishi that sometimes would not produce heat after the temp knob was moved from full cold to heat. Turned out that the blend door actuator would get intermittently get stuck in the fully closed position. I followed the cable down to where it entered the duct work and installed a small block of wood to prevent the cable from being moved to the fully cold position. The difference was maybe a 16th of an inch at the knob end.
Car had heat for 3 winters until other issues signaled it's demise.
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DerbyDad03 wrote:

Not the problem , I can observe the mechanism moving when I move the control knob . Unless there is a t-stat in there that controls them and the cable only signals it for heat .
--
Snag



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On Friday, October 30, 2015 at 10:19:22 AM UTC-4, Terry Coombs wrote:

What mechanism can you observe move? On the Mit, I could see the cable move a nylon connector over it's full range of motion as observed from outside the blend door housing. However, the blend door shut motor itself is inside the housing and that was what was intermittently failing in the fully closed position - by design.
If you fast forward to 7:00 in the following video, you'll see what I mean.

https://www.youtube.com/watch?v=HywkYSNRGug

What I did was keep playing with the control knob until the shut motor activated and opened the doors. I then physically prevented the cable from ever moving to the fully closed position, thereby "eliminating" the shut motor from the system.
My Dad has a mid-2000's Mercury Sable. He had poor heat also. He had a blend door issue, but it cost him $800 to fix. It was mostly labor because half the dash board had to be taken apart to get to the problem.
Blend door issues are a common cause of no/low heat.
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On Fri, 30 Oct 2015 07:50:05 -0700 (PDT), DerbyDad03

with the water control valve. The control shaft pulled out of the "spool valve" that controls the water flow - moving the shaft opens a roughly 1/4 inch hole instead of the 5/8" hole it is supposed to open.
I replaced a few dozen of those (and on some other Toyotas as well) Remove the valve and check it carefully.
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snipped-for-privacy@snyder.on.ca wrote:

Valve has been removed and checked , I get full range of motion and it stays put on the shaft . On the blend door thing , I'm observing the levers and stuff on the top of the heater outlet , all seems to be working properly . I can actually hear the doors inside moving when I move the control lever .
--
Snag



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wrote:

appear to be good when looked at, when the heat is working. The trick is to remove the valve when the heat is NOT working and confirm.
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Terry Coombs wrote:

Do you feel heat?
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Tony Hwang wrote:

Answered above (or below) , the hoses are both very hot when it works right , in is hot and out is not as hot when it's malfunctioning . That indicates to me that there is not enough flow thru the core .
--
Snag



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On 10/30/2015 2:31 PM, Terry Coombs wrote: ...

But you say this is intermittent--works sometimes but not others?
--


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dpb wrote:

It will work fine sometimes for a few minutes or a couple of hours and maybe even a whole day or two after I fiddle with it . It did seem to come back when we were driving around town today , but who knows , it's warm enough without heat today .
--
Snag



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On 10/30/2015 4:07 PM, Terry Coombs wrote:

are intermittent themselves?
That was a biggie with one of the series of Chebby pickumups in '97 or thereabouts...the dampers are electric motors and combined with their tendency to lock up and then burnout the motor the actual control circuitry was subject to a service bulletin that wasn't a recall but if the customer complained they'd swap it out...
--


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On 10/30/2015 3:31 PM, Terry Coombs wrote:

Could be a piece of crud floating around? Partly blocks the water, then floats a bit and opens the passage for good flow?
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Ed Pawlowski wrote:

That's about the only explanation I can come up with too . I just can't figure out where/what it is and how to get it out .
--
Snag



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Terry Coombs wrote:

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overheating, while on other engines it could cause the engine to never get up to operating temperature. If running without a thermostat it is a real good idea to install a restrictor plate or baffle with a roughly 3/4" hole in place of the thermostat.
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