Hit-or-Miss Heating

On Mon, 14 Dec 2009 06:59:43 -0500, "J.B. Wood"
> wrote:

>Hello, all. My 1990 Mercury Sable has lately been displaying some
>unusual heating behavior: With the passenger compartment temperature
>set at 85F I only get cold air coming out of any of the ducts even when
>the engine temp is nominal (mid range on the temp gauge). The weird
>thing is that after I drive the car to work and it sits outside all day
>I always have loads of heat available when driving home. The coolant
>level is where it should be and the water pump and thermostat were
>recently replaced. Does anyone have an idea? Thanks for your time and
>comment. Sincerely,

First thing to do is make sure the engine temp really is up where it
needs to be. I don't think this is your problem but it is an easy
place to start. Also check your heater hoses and make sure both of
them are hot. Two hot hoses tells you there is coolant circulating
through the heater core.

You said you set the temp to 85 which tells me the car has an
automatic climate control system and I think this is probably where
your problem actually is. Most common is a blend door that is
sticking. When that door doesn't move the air isn't directed through
the heater core so... no heat. It could also be a problem with the
temperature sensors not knowing the temp of the car or just a general
fault with the automatic system.

If you aren't used to working under the dash and you don't have arms
with five elbows I would probably find someone that does a lot of this
type work

Steve B.

On 12/14/2009 11:37 AM, hls wrote:
>
> "dsi1" > wrote in message news:jKxVm.46756
>> I don't think there's any problem with coolant flow through the heater
>> core. I'll bet your problem is the blend door in the heater box. I
>> don't know how you would check/repair something like that.
>
> I dont know about Sable. On some cars you can get to them well enough to
> manually operate the doors. If they are vacuum operated, you have
> another burden to bear.

I don't know anything about these systems because in the past, if it
went bad, I'd just run without the heater. The idea of working under the
dash is pretty unappealing - thank God I live in the tropics. My guess
is that the Ford uses vac servos to operate the doors and one could do
an initial check with a hand held vacuum pump. I'll bet the system tends
to leak when the rubber hoses are cold.

>
> If the doors are stuck, you can sometimes free up the mechanical pivots
> of the blend doors with a little shot of aerosol lubricant.
> A Sable mechanic would likely know all the systems.
>
> I dont understand why this system would work in the afternoons, but not
> in the mornings,and now wont work at all. I am sure it will make sense once
> he gets into it
>
> Really helps to have a good manual when you are trying to DIY something
> like this.

"dsi1" > wrote in message news:d5AVm.80866
>
> I don't know anything about these systems because in the past, if it went
> bad, I'd just run without the heater. The idea of working under the dash
> is pretty unappealing - thank God I live in the tropics. My guess is that
> the Ford uses vac servos to operate the doors and one could do an initial
> check with a hand held vacuum pump. I'll bet the system tends to leak when
> the rubber hoses are cold.

There are different systems and you really have to know what you are doing.

Some GM systems, for example, us a vacuum modulator module that is a little
difficult to diagnose without the proper tools,and is DAMNED expensive to
replace. This system operates blend doors, etc.

Sables and Tearasses are just something I dont know anything about, and
really dont want to learn.

I wish it were as simple as it used to be, with just a manual linkage to the
blend doors, a simple valve, etc. But it isnt always that way.

mvh

dsi1 > wrote:


> On 12/14/2009 6:51 AM, J.B. Wood wrote:

> > 2. There have been several isolated instances where the temperature
> > indicator (engine has been running for a while) has gone to its maximum
> > value and just as quickly dropped down below below the midpoint before
> > returning to the midpoint. My conclusion here would be low coolant but
> > the coolant appears to be full. I'm speculating that something is
> > restricting coolant flow such as a partially-blocked radiator or
> > somewhere else other than the heater core but before the thermostat. Any
> > further insights are most welcome. Sincerely,
> >

> You should verify that your coolant level is OK and there's no leaks. If
> that's the case, change your thermostat. I think that your heater
> problem is unrelated to your coolant problem.

It certainly sounds like an air bubble. Just to be sure, are you checking
the coolant level in the cooling system itself rather than in the
overflow tank? Wait until the engine is dead cold and then remove the
remove the pressure cap. Top it up. After the initial fill you need to
"burp" it--run it through a full temperature cycle with the heater on--
then top it up again. After that you can leave the cooling system
sealed and simply watch the fill lines on the overflow tank.

then "burp" it. h
--
Jack Myers / Westminster, California, USA

An expert is a person who has made all the mistakes that can be made in a very narrow field..

- Niels Bohr

On 12/14/2009 8:47 PM, Jack Myers wrote:
> > wrote:
>
>
>> On 12/14/2009 6:51 AM, J.B. Wood wrote:
>
>>> 2. There have been several isolated instances where the temperature
>>> indicator (engine has been running for a while) has gone to its maximum
>>> value and just as quickly dropped down below below the midpoint before
>>> returning to the midpoint. My conclusion here would be low coolant but
>>> the coolant appears to be full. I'm speculating that something is
>>> restricting coolant flow such as a partially-blocked radiator or
>>> somewhere else other than the heater core but before the thermostat. Any
>>> further insights are most welcome. Sincerely,
>>>
>
>> You should verify that your coolant level is OK and there's no leaks. If
>> that's the case, change your thermostat. I think that your heater
>> problem is unrelated to your coolant problem.
>
> It certainly sounds like an air bubble. Just to be sure, are you checking
> the coolant level in the cooling system itself rather than in the
> overflow tank? Wait until the engine is dead cold and then remove the
> remove the pressure cap. Top it up. After the initial fill you need to
> "burp" it--run it through a full temperature cycle with the heater on--
> then top it up again. After that you can leave the cooling system
> sealed and simply watch the fill lines on the overflow tank.
>
> then "burp" it. h

It's surprisingly tricky to fill radiators these days because they tend
to be lower than the top of the engine. On my Taurus, I can tell if it's
full by squeezing the top radiator hose. The first time I changed the
coolant in the car, I loosened the clap on the hose that went to the top
of the engine. Now days I don't bother - I'll just run it through
several heating a cooling cycles and purge air bubbles by squeezing the
hose.

On Dec 14, 6:59*am, "J.B. Wood" > wrote:
> Hello, all. *My 1990 Mercury Sable has lately been displaying some
> unusual heating behavior: *With the passenger compartment temperature
> set at 85F I only get cold air coming out of any of the ducts even when
> the engine temp is nominal (mid range on the temp gauge). *The weird
> thing is that after I drive the car to work and it sits outside all day
> I always have loads of heat available when driving home. *The coolant
> level is where it should be and the water pump and thermostat were
> recently replaced. *Does anyone have an idea? *Thanks for your time and
> comment. *Sincerely,
> --
> John Wood (Code 5550) * * * *e-mail:
>
> Naval Research Laboratory
> 4555 Overlook Avenue, SW
> Washington, DC 20375-5337

I just read a couple of TSB's on the blend door having issues with the
cable etc.. It also mentioned something to the effect if you are
having a problem with the blend door turn the key off and back on and
see if it works then.

On Dec 15, 11:34*am, m6onz5a > wrote:
> On Dec 14, 6:59*am, "J.B. Wood" > wrote:
>
> > Hello, all. *My 1990 Mercury Sable has lately been displaying some
> > unusual heating behavior: *With the passenger compartment temperature
> > set at 85F I only get cold air coming out of any of the ducts even when
> > the engine temp is nominal (mid range on the temp gauge). *The weird
> > thing is that after I drive the car to work and it sits outside all day
> > I always have loads of heat available when driving home. *The coolant
> > level is where it should be and the water pump and thermostat were
> > recently replaced. *Does anyone have an idea? *Thanks for your time and
> > comment. *Sincerely,
> > --
> > John Wood (Code 5550) * * * *e-mail:
>
> > Naval Research Laboratory
> > 4555 Overlook Avenue, SW
> > Washington, DC 20375-5337
>
> I just read a couple of TSB's on the blend door having issues with the
> cable etc.. It also mentioned something to the effect if you are
> having a problem with the blend door turn the key off and back on and
> see if it works then.

I had a heat problem in a Taursu casued by a clogged heater core.
There is a bypass hose right across the input to output of the core
located on the firewall so just becasue you have flow through the
heater core hoses doesn't mean the flow is actually going through the
core, if the core is clogged, the flow will go through the bypass
hose.

I carfully pinched the bypass hose with vise grips to force flow
through the core and back flused the core. that fixed it for me....
YMMV.

Mark

On Dec 14, 3:59*am, "J.B. Wood" > wrote:
> Hello, all. *My 1990 Mercury Sable has lately been displaying some
> unusual heating behavior: *With the passenger compartment temperature
> set at 85F I only get cold air coming out of any of the ducts even when
> the engine temp is nominal (mid range on the temp gauge). *The weird
> thing is that after I drive the car to work and it sits outside all day
> I always have loads of heat available when driving home.

There is an in car temp sensor behind the glove box and a sun temp
sensor under the left side of the dash.
If there is no air in the system, I'd take a look at those.
HTH,
Ben