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 .
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.
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
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.
On Fri, 30 Oct 2015 07:50:05 -0700 (PDT), DerbyDad03
Not sure about your year, but many earlier 4-runners had a problem
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.
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 .
Whatever is happening is intermittent. I HAVE seen the heater valves
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.
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 .
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 .
Makes me suspect a loose obstruction hanging up or perhaps the controls
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...
Removing the thermostat on some engines will cause serious
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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