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Thermal Switch
Posted by Stephen Goldberger (more from Stephen Goldberger) on Mon, 28 Jan 2002 11:45:55
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

You may have seen the following item for sale on the TSN classifieds:

from SaabTech Specials 
For Sale: 3 Wire Thermal Switches 

Time for some SaabNet Support here. Im having a sale on the 3 wire thermal 
switches that turn the radiator fan on.'

http://www.saabnet.com/tsn/forms/saabtech.html


I'd like to elaborate. The switch in question replaces the original Saab
switch for middle period turbo models, those with two speed cooling fan
circuits. Early and middle period 9000 models have the cooling fan
thermoswitch located at the coldest spot on the radiator - just above the
outlet to the water pump.  And as is usual for water cooled engines, the
therostat is located at about the hottest part of the water jacket - the
location where the  the cooling water leaves the head.

The switch settings for the original Saab part engage the cooling fan on
low speed at approximately the thermostat opening temperature, and the high
speed at approximately 100C, the atmospheric boiling point of water.  What
this means is that when the cooling fan engages at low speed, the water
entering the engine from the radiator is already at the engine's 'normal'
operating temperature.  Since the engine is always adding heat to the
water, that means that the engine will run  above it's 'normal' temperature
so long as the operating conditions require the fan.  The fans don't run at
high speed until the water at the coldest part of the radiator is at the
boiling point, so if the operating conditions require the fans to be at
high speed, the engine will be running 'plenty hot.'  The replacement
switch sold here has its set points about 10C lower than the original Saab
part, which results in the engine running that much cooler during the
summer.  Whether having the engine run that much cooler makes a real
difference in engine life is debatable, but there is no doubt that it is
annoying to have the temperature gauge pointing at the visor pivot all
summer long is annoying.   I installed one of the referenced thermal
switches in my '91 9000T, and the the gauge staying close to horizontal in
warm weather.  As a digression, I found when I installed the switch that my
car was incorrectly fitted with a single-temperature (two wire) switch that
was connected to engage only the low fan speed.

The radiator cooling fans on 9000 models from 1995 on, and all NG 900, 9-3,
and 9-X cars, are controlled by the car's computer(s), using data from the
engine temperature sensor.

Stephen Goldberger, Editor and Publisher
NINES, the magazine of the SAAB Club of North America
vist our web site at http://www.saabclub.com
==================
The Saab Network
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Posts in this Thread:
StateOfNine.com
SaabClub.com
Jak Stoll Performance
M Car Covers
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