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Re: Bypass Valve
Posted by Ramblerdrver - http://saabnet.com/tsn/forms/e.php3 (more from Ramblerdrver - http://saabnet.com/tsn/forms/e.php3) on Thu, 26 Feb 2004 02:34:16
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

By bypass valve, do you mean the heater valve that's under the dash?      If
so, then likely the two 't' fittings are letting the coolant bypass the
heater core all the time...the coolant is following the path of least
resistance.   To make it work you'd need to haveÊlosable Êalve in the hose
between the 't' fittings.
 
If you indeed got under the dash and replaced the heater valve with 2 't'
fittings while on a trip, you certainly deserve an award for effort!
 
Steve Parsons 98 900, 99 9-5,
==================
Message from David Prantl - http://saabnet.com/tsn/forms/e.php3?em=38

Chris,

The heater bypass valve you're talking about was added to classic 900 models
in 1991.  The intention was to block off coolant flow to the heater core if
the coolant got too hot.  Somewhat counter-productive, since on old cars it
is generally accepted practice to turn on your heater when the engine is
overheating to help cool it down.  This bypass valve removes this option of
extra cooling through the heater.  Anyway, what you have done with the two
tees and a hose between them is open up the bypass path permanently.  Since
the heater path is not closed off, some coolant still makes its way through
the heater.  But since the bypass path is the path of less resistance, most
of the coolant takes that path, and you have very little heat.

Here's your original hose setup with the bypass valve:
http://bellsouthpwp.net/d/a/davidprantl/saab/c900cool2.jpg


Here's what more than one hundred thousand classic 900 cars ran with for many
years before 1991:
http://bellsouthpwp.net/d/a/davidprantl/saab/c900cool1.jpg


The best thing for your car would be to convert it to the earlier hose setup.  You can do this
either by installing the earlier hoses, or by putting in straight hose-splicers instead of
the tees you now have, or by removing your custom permanent bypass hose and capping off the
open ends of the tees.  I would recommend brand new old-style hoses.  The part numbers are
75 45 544 and 75 41 527.  They cost six dollars and ten dollars respectively at HREF='http://www.eeuroparts.com'>http://www.eeuroparts.com


David Prantl

'84 900S, 5M, 210kMi, RIP as of 2/98
'89 900, 3A, 116kMi, restored and SOLD on 3/24/01
'97 9000CSET, 5M, 63kMi, Speedparts Stage-I, SOLD on 10/11/02
'93 9000CSET, 5M, 84kMi, SOLD on 3/8/03

'86 9000T, 5M, 200kMi
'86 9000T, 5M, 205kMi
'88 9000S, 5M, 142kMi
'90 9000S (B202I), 4A, 162kMi
'94 9000CSE (B234I), 4A, 165kMi
'68 97 Sonett V4, 4M, 76kMi, #000467
==================
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