On Fri, 30 Oct 2015 09:40:04 -0500, "Terry Coombs"
wrote:

Larry Jaques wrote:
On Fri, 30 Oct 2015 07:52:30 -0500, "Terry Coombs"
wrote:

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 .

First off, make sure you have a tstat in there. The engine's
thermostat is necessary to allow the radiator water to warm up to
proper temp for delivering how air through the core. In addition to
that, the water pump is responsible for flow. I've seen water pump
impellers eaten down to nothing via electrolysis and rust, so don't
rule that out.

There is a t-stat , motor comes up to op temp in a reasonable time . I
hadn't considered a prob with the impeller , but doubt it's the problem - I
think there's an intermittent blockage but I can't find it .

You said you checked the water control valve, and it's OK, as is the
heater core? Restrictions there are usually the culprits if the water
pump and thermostat are operative. Make sure that the water control
valve for the heater is properly adjusted. Some are extremely picky,
especially if the water pump impeller is diminished. Also, try to see
if the water control valve gate is loose from the arm. I've seen the
shafts break but the arm not fall off.

Valve operates correctly and is not broken .

You are 100% sure? Did you take the hoses off both ends and look to be
sure when the shaft moves the plunger or "spool "moves too? VERY
common problem on earlier Toyotas - not sure if 99 had the problem or
not. As Toyota service manager I had a LOT of them replaced.

As to heater core flow, can you blow a full lungful of air through it
without any back pressure whatsoever? Maybe boil it out, just to be
on the safe side? (Egad, it has been so long, I don't remember what
that entails any more!) If in doubt, go to a Toyota dealership and
blow through a replacement core to note the difference.

Let us know what you find. Curious minds, etc.


Core shows no sign of restriction when I run water thru it . I'm not
inclined to completely disassemble the dash to pull the core . I was sure
I'd find a hose with a degraded inner layer that was blocking the flow , but
the hoses are all in like-new shape , and I'm stumped . My next step is to
drain the whole system again and run some kind of chemical flush thru it ,
it's possible there's a flake of something floating around the intake man
passages , but I don't understand why it doesn't flow out to thru the t-stat
into the rad if that the case . I'd much prefer the wife to be warm rather
than hot , if you know what I mean .