Overcooling and the MOT
26 May 2007, 81,767
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he 9-3’s coolant temperature took an unusual turn on the way to
Overcooling could point to a stuck thermostat and the heater output
would be poor. The 9-3’s coolant gauge
is controlled by the ECU so if the temperature
sender unit had failed it would impact on many other Saab features, most
obvious being the automatic air conditioning. If the automatic air conditioning believes
the coolant temperature to be cold it will drop the fan speed to minimum to
prevent flooding the interior with cold air.
The heater fan speed rose and the Saab started toasting me.
The thermostat could be faulty except since that morning the 9-3 has
been warming up just as quickly as always.
This could point to the thermostat having been faulty since I picked the
Saab up of course...
This incident could show the weakness of modern coolant gauges. Older generation coolant gauges use a sender
unit linked to a gauge and these showed the subtle changes in coolant
temperature. Danielle,
Geoffrey and Melissa
all used older generation gauges. More
modern designs have a gauge that shows what the ECU
wants you know. They also control the
cooling fans too.
Now the reason why dashboards show what the ECU
want you to see is because most people don’t spot the subtle differences in
reported temperatures and also that cooling systems are robust enough such that
a slight increase in temperature is nothing to be worried about. When the 9-3 is bogged down in heavy I very
rarely see the coolant temperature needle deviate from the horizontal position
but it’s likely that the coolant temperature rises and falls as the fan cycles
in and out. Do I need to know about
this? No, perhaps not - but sometimes it
is handy!
Anyway, my suspicion is that the car has a slightly lazy
thermostat. I’ll monitor what happens
and in all likelihood, have it replaced no later than the next time the coolant
is replaced.
Otherwise, Chef has just been through his MOT with a few advisories.
First, both rear dampers are leaking.
My suspicion is that these are the original dampers and the car has been
used for some towing, not much, but some nevertheless. These dampers will sooner or later need to be
replaced. Thing is, replacing just the
rear dampers is arguably not sensible when the fronts have over eighty thousand
miles of wear on them.
Second, the wiper blades are not effective. As it happens, the wipers work great when
they’ve been soaked in rain for at least an hour. These too do need to be replaced since they’ve
been on the car for at least a year.
Actually I can’t remember when the 9-3 had decent wiper blades apart
from the headlights.
Third, Nidd Vale advised me that given the age of the car it should have
an air conditioning service: regassing.
I have never had to have an air conditioning system regassed and I’m not
about to start - at least pending research that hasn’t been sponsored by an air
conditioning fluid manufacturer!
The dealer commented that all four discs were either pitted or scored
all around.
Finally, there is a chip on the windscreen. This is something I do need to get
fixed. Unfortunately, I’ve been too lazy
to get it fixed so far.
As far as the other aspects of the MOT go, the car passed the soot test
with no issues or complaints. The four
runs produced a smoke figure of 2·49, 1·74, 0·76 and 0·56 for an average of
0·91. The maximum permitted limit for
this 9-3 is 3·00, so this result isn’t bad but not brilliant. This is when running on BP Ultimate Diesel,
which is visibly less sooty than all other diesels I’ve tried.
All up then I’m pleased that the 9-3 passed the MOT without requiring
any additional work. The dampers do need
attention but this can be deferred for the time being. As the rear dampers condition worsens so the
ride and handling will also worsen, but depending on how quickly this happens
depends on how quickly I have them replaced.
It’s possible that they’ve been leaking for some considerable time now.