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Cooling Help
Posted by markus.jaervi (more from markus.jaervi) on Thu, 18 Oct 2001 00:56:15
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

I will try to help with the cooling related question:

The first step is to reconnect the original fan wiring and the
temperature gauge.

The cooling system is designed to work as follows:

At startup thermostat is closed and water circulates in engine
block. After a while of constant driving the engine will reach
operation temperature and thermostat will open to allow flow through
radiator and the thermostat will keep the temperature at 82 or 88
deg.

Once you stop for a longer period, like in stop-and-go traffic, the
thermostat opens wide open but due to lack of air flow through
radiator the engine temperature rises and the gauge will eventually
reach 10 o'clock, engine coolant temperature is about 90 deg c and
the cooling fan starts. The gauge starts to fall back down and
within a minute or two it should be back to approx centre with 88
deg c thermostat or 8 o'clock with 82 deg thermostat. Fan will stop
and the temperature will start to raise until the cooling cycle
starts again. This is how the system is intended to work and is no
indication of overheating. The cycle is designed in the system to
reduce cooling fan on-time thus reduce electric load. Not only
Saabs, but most other cars with electric cooling fan have a similar
design.

Many are concerned of the problem because the temperature gauge
reading range on the Saab is narrow, about 75-95 deg C, and clearly
shows temperature variations of a degree.  On many other cars the
temperature gauge will have a broad range of  40 - 120 deg C. While
2 deg C rise in temperature will show as a noticeable movement (10
o'clock) on the Saab gauge, you wouldn't  be able to notice it on
the other make.  This feature enables to use the gauge for
troubleshooting:

If the temperature gauge does rise well above 10 o'clock, but only
while standing still, then you have a cooling fan problem, fan
switch, relay, wiring or fan itself, and should repair it right
away.

If the the temperature rises well above gauge centre  while cruising
on flat, then you have a problem with a stuck thermostat, blocked
radiator fins, clogged radiator or blocked engine cooling passages.
The Saab waterpump will work until it starts to leak and even then
it will still pump so I would check it last. On a hot day, climbing
up a steep hill with the pedal on floor, the temperature may rise
even just below red (95 deg) but it's still ok, it's not in red (for
comparison a Mercedes would show a bit above 8'oclock here). The
thermostat is wide open and will now additionally close the passage
to the heater core to ensure all the coolant is flowing through
radiator to ensure maximum cooling. If the temperature crawls to the
red then it's time for a break. If the problem persists the cooling
system should be serviced.

The engine is truly overheting only after the coolant starts
boiling. This will not happen until at above 110 deg C due to
pressurized cooling system and by this time your temperature gauge
will be well in or above red.

I don't know why Saab has ended up using this gauge. Maybe it is due
to strict tempereture requirements of early turbos. What I know is,
it's good for troubleshooting, and once you know how the system
works and what the temp scale is, you won't be worried at all about
'10'o clock' !

Markus Jarvi
-92 9kcs 2.3i man
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