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Re: Heating and Cooling
Posted by Peter Adler (more from Peter Adler) on Wed, 14 Mar 2001 12:21:53
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

See TSN #10806 9/17/97 for an explanation.
Sorry, when I tried searching for that msg # in the archives at
http://www.escribe.com/automotive/european/tsn/
the resulting message

#10806 only shows the question, not the answer.  I've copied the answer
below.  Also see #10908 9/26/97, which is a more detailed explanation
from Ywan Mason.

http://www.escribe.com/automotive/european/tsn/m16489.html


Message from RichM93147
I've been dealing with this same problem lately on my '87 900S.  From what I
have been able to determine, this behavior is by design, more or less. In
section 261 of the Bentley manual for our cars, the thermostat is described
as having three stages.  Stage one: coolant is cold and flows through engine
and heater core.  Stage two: engine has warmed up somewhat and coolant is
allowed to flow through the whole system, including the radiator and heater.
 Stage three: engine has reached operating temperature and most flow to the
heater is cut off - only a small amount goes to the heater via a small bypass
opening in the thermostat housing (see diagram on p. 261-2 in Bentley
manual).  I find it very odd that the people who built an otherwise very
intelligent car have somehow reasoned that we won't need heat in the cabin
once the engine is warm.  Especially odd for designers living in a cold
climate!  I wonder what they do when they get cold?

Archive searches through this net, and correspondence with other members has
indicated that a fix for this problem is to drill a few small holes in the
heater bypass plate of the thermostat, basically defeating whatever purpose
Saab had in mind for this weird design.  Four 1/8-inch holes is what has been
suggested to me.  I can't see any reason that this would cause harm to the
car.  I would be very interested in any information you receive in response
to your posting (you can e-mail me direct at richm93147no39sdcx6spamx782aol.com).  By the
way, there was also a technical service bulletin about poor heat that had to
do with insufficient coolant flow at RPMs less than 1500, and the fix is to
install a supplemental coolant pump. But from what you have described, and
from my own analysis of my car's behavior, I doubt that is the problem for
either of us.  I am going to try the hole dilling thing first chance I get.

Good Luck!

Rich McLellan
--
Pete Adler
'91 900 SE T Conv (Monte Carlo Yellow)

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