Temp gauge rises - no cabin heat

On Jan 26, 2:13 pm, "John" <j....TakeThisOut@myhmg.org> wrote:
> Here's the situation, looking for confirmation on my possible diagnosis or a
> point in another direction.
>
> 1989 900 T
> Engine up to temperature and idling in a parking lot with the outside
> temperature around 20 degrees F.  The temperature gauge starts climbing and
> at the same time the cabin heat starts blowing cold air.  Once we start
> driving again the heat comes back and the temp gauge goes back to normal.
>
> Are we talking a bad thermostat here or am I way off base?

The cabin heater matrix has a thermostatic valve in. When the
temperature comes back down (while driving) it is allowed back into
the cabin.
Does the temperature rise up to an indicated red on the gauge? Is the
radiator fan working? Check this by baring back the terminals on the
radiator thermostatic switch and bridging the terminals with something
metal (insulating yourself from the voltage, of course). Does it come
on at about 2/3 - 3/4 up the gauge? Check the fuse.
One final things - there is a small hose that runs from the top of the
radiator to the coolant expansion tank - feel it. Is it cold? If so,
it's blocked ... most likely at the expansion tank end spigot. That
may cause an airlock where the radiator thermostatic switch is, so the
radiator will not work ... overheating.

You can change the thermostat - go for an 89 degree one. Might as well
anyway for what they cost - check out the things above and report
back. We should be able to get this one sorted between us.
 >> Stay informed about: Temp gauge rises - no cabin heat 

"John" <john.RemoveThis@myhmg.org> Jan 26, 2008 at 09:13 AM


>Here's the situation, looking for confirmation on my possible diagnosis
or
a
>point in another direction.

>1989 900 T
>Engine up to temperature and idling in a parking lot with the outside
>temperature around 20 degrees F. The temperature gauge starts climbing
and
>at the same time the cabin heat starts blowing cold air. Once we start
>driving again the heat comes back and the temp gauge goes back to
normal.

>Are we talking a bad thermostat here or am I way off base?

>TIA

I second the previous comments about coolant levels, temp senders, fans
and the like. It may also be worth checking for a collapsed hose -
especially the very long one. Cheers



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 >> Stay informed about: Temp gauge rises - no cabin heat 

John ("John" <john RemoveThis @myhmg.org>) gurgled happily, sounding much like they
were saying:

> 1989 900 T
> Engine up to temperature and idling in a parking lot with the outside
> temperature around 20 degrees F. The temperature gauge starts climbing
> and at the same time the cabin heat starts blowing cold air. Once we
> start driving again the heat comes back and the temp gauge goes back to
> normal.
>
> Are we talking a bad thermostat here or am I way off base?

No, you've got the RIGHT 'stat installed.

The genuine Saab 'stat has three stages, not the usual two.

1. Block only, warm-up.
2. Full circuit, normal.
3. Rad & block only, over-temp. Heater is cut out of the loop.

First call would be to change the coolant and flush it all through -
there's a block drain under the exhaust manifold (probably seized) and
the rad drain under the RH (US passenger side) of the rad.

When you've got nice shiny new coolant in, turn the ignition on (don't
start the car), unplug the two plugs from the rad temp switch (top LH of
rad) and short between 'em. The fans should come on. If not, that's your
problem. If they do, then start the car, and run it up to temp. If the
fans don't come on as it gets to half-scale on the temp gauge, then the
switch is at fault.
 >> Stay informed about: Temp gauge rises - no cabin heat 

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 >> Stay informed about: Temp gauge rises - no cabin heat 

"still just me" <wheeledBobNOSPAM RemoveThis @yahoo.com> wrote in message
news:6jjqp39g5ot2thvcfnvjqguccksek9imjp@4ax.com...
> On Sat, 26 Jan 2008 09:07:46 -0700, Bill Jeffrey
> <wjeffreyAT RemoveThis @alum.DOTmit.edu> wrote:
>
>>
>>In my limited experience with an American car, this is caused by low
>>coolant level.With the engine at idle, the level is too low to reach the
>>heater core. As the RPMs come up, the water pump flogs the coolant more
>>strongly, and some of it reaches the heater core inlet.
>>
>>Possibly also the water pump itself - or the belt driving it.
>
> I agree - possible low coolant (easy enough to check) but likely a bad
> WP or belt.
>
>

Turned out to be a slow coolant leak, which then turned out to be a much
faster leak during diagnosis.

Thank you!
 >> Stay informed about: Temp gauge rises - no cabin heat