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Coolant temp issue

3K views 13 replies 9 participants last post by  hvaclander 
#1 ·
I've recently started having some issues with my temperature gauge. I've read plenty of instances where folks have replaced the thermostat and/or coolant temperature sensor and plan on replacing both soon since it is a relatively low-cost repair. I am curious about the problem though as from what I have read I have some symptoms of a bad thermostat and other symptoms of a bad temp sensor.

When I start the car and let it warm up (at idle), the sensor reaches operating temperature after about 5 minutes (depending on the temp outside, obviously). As I start driving, however, the temperature will drop. Alternatively, if I start driving the car without letting it warm up to operating temperature, the temperature never rises.

Any thoughts on what would cause the temperature (or maybe just the gauge?) to drop once the vehicle has been moving for a while?
 
#2 ·
I would drain the coolant, flush it, fill with new, do thermostat and temp sensor. Give everything fresh start. You might also wanna clean out the heater core. I just took the lines off at the engine and filled it with bleach and then ran water through it after I let it sit for a bit. It could be anything from a small blockage, air maybe, to a failing sensor or thermo. After all this, it still does it, could be an issue with the cluster but I am going to doubt that 99.9%.
 
#3 ·
Thanks for the advice, I will likely do the full flush and install a new thermostat and temp sensor. I might try just swapping out the thermostat and temp sensor without doing a coolant flush if it looks like I'll be able to get the job done without losing too much coolant, but from what I've read it seems like that is difficult.

The part that confuses me though is why the engine reaches operating temperature when it is started and left idling, but loses temperature when driving. Any thoughts on that?
 
#8 ·
Thanks for the input everyone. I think I'll do the replacement this weekend if my local Saab repair shop has a temp sensor in stock, otherwise I'll have to wait until they get one for me.

I'm not due for a coolant change - anyone know the easiest way to do this while losing as little coolant as possible?
 
#10 ·
You will likely lose a fair amount but you need to remove the hose on the housing and then pull out the thermostat if it isn't already stuck to the housing. No real other way.But it is towards the top of the engine so you won't lose a whole lot. You should be able to get away with just topping it off with distilled water from say Walmart or something. Tho since your in Canada might just want to get one bottle of anti freeze and top it off with that.
 
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