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Discussion Starter · #1 ·
My '07 9-3 is reading error code P0128, coolant temp low. I've looked up how to replace the thermostat, but I wanted to know if this would be safe to drive in the meantime. If I keep the cabin heat/blowers off, the gauge seems to stay in the middle as it should, but seems to get there quicker than usual (especially for New England November weather) and fall quicker than usual once the car is off. I've noticed that if I turn the heat on along with the blowers in the cabin, the temperature goes down about an eighth every two minutes, stopping at a quarter on the gauge. I haven't seen anyone report any similar findings to this minus the error code, so I was concerned maybe it was something other than the thermostat? Maybe an overactive cooling fan?
 

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I had a similar issue, minus the error code. It was the thermostat stuck open...highway driving in the winter with low ambient temps would cause the car to go from operating temp to running too cool (2 way to operating temp on dash coolant temp gauge). New thermostat fixed the issue, I flushed the coolant at the same time just because. Running cool puts a decent amount of excess wear & tear on the engine & impacts your mpgs quite a bit as well.

If you have techII you can check the function of the rad fans very easily but it sounds like a stuck/sticking t-stat (luckily sticking open).
 

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Crank it, let it run for a few min and check your radiator hoses. If its (hoses) are cold, your thermoset is at fault. If you drive it, with the interior fan on high, and it drops quickly, Its your thermostat. Are your radiator fans coming on? You might be able to check them by touching a screwdrivers to the two terminals at the sensor in the radiator, if the fan kicks on, you're ok, it's the thermostat. Long story short, Change the thermostat. That is the beginning of the engine cooling, before it is dumped back into the engine. May I also suggest the Bentley manual for your model Saab. HTH.
 

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Discussion Starter · #4 ·
Crank it, let it run for a few min and check your radiator hoses. If its (hoses) are cold, your thermoset is at fault. If you drive it, with the interior fan on high, and it drops quickly, Its your thermostat. Are your radiator fans coming on? You might be able to check them by touching a screwdrivers to the two terminals at the sensor in the radiator, if the fan kicks on, you're ok, it's the thermostat. Long story short, Change the thermostat. That is the beginning of the engine cooling, before it is dumped back into the engine. May I also suggest the Bentley manual for your model Saab. HTH.
Yeah, it drops very quickly with the interior fans on high, thank you! I'll look into changing my thermostat!
 

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Discussion Starter · #5 ·
Crank it, let it run for a few min and check your radiator hoses. If its (hoses) are cold, your thermoset is at fault. If you drive it, with the interior fan on high, and it drops quickly, Its your thermostat. Are your radiator fans coming on? You might be able to check them by touching a screwdrivers to the two terminals at the sensor in the radiator, if the fan kicks on, you're ok, it's the thermostat. Long story short, Change the thermostat. That is the beginning of the engine cooling, before it is dumped back into the engine. May I also suggest the Bentley manual for your model Saab. HTH.
Just making sure, you mean the thermostat below the heat shield and coolant tank, right? Not the one near the ECU?
 

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They both measure coolant temperature. Temperature is the key word. The thermostat measures temp via a spring loaded coil on a valve, that opens and closes when it hits a certain temperature (180-210), then the flow of water and coolant goes to the Radiator where it is cooled and sent back to the engine to start the process again. The coolant temp gage (sensor) goes to the instrument cluster and displays the temp reading. Hth
 
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