Overheating

[Roxi]

2005 9-3 linear when its only ideling does not overheat , when i start driving can not get even a block and the temp guage spikes in the red. Could this be a bad or stuck thermostat?

[Digger]

If you're lucky it's a stuck thermostat.
If you're really lucky it's a bad temp sensor.
A few questions before rendering an opinion.
Which engine?
How many miles on the motor?
Auto tranny or stick?
Have you checked your coolant level?
Is your radiator full of coolant?
Do you loose coolant when or after your gauge shows hot?

[Roxi]

2.0 ,140k, auto, yes the coolant is full after temp guage spikes. It does not seem the engine is as hot as the guage shows, I can take off the cap after it spikes with very little or no steam. The hoses are hot not hot enough that i cant touch.

[Digger]

Things you can check without tools and test equipment.
When everything is cold and before you start the engine, squeeze the top radiator hose several times, you should be able to slosh the coolant and see the level change in the expansion tank.
Start the engine, turn the AC on full cold and look under the hood to see it your cooling fan is running. Turn on the heat full high with heater fan on high drive around the block to see if you have hot air blowing from the vents before and after the temp spikes to the red.
What you're checking here is cooling fan operating, big air bubble in cooling system, (something that can happen over time from a pinhole hose leak) and the water pump. Soon as it's showing hot turn it off and squeeze the upper hose again. With heat comes pressure, if you're really hot and the thermostat is stuck you should have hot air blowing through the vents and the radiator hose should be stiff and hard to squeeze, the heater in and out hoses should be close to same temp when touched and you should have gotten a little farther down the road before your gage spiked.
If you weren't able to slosh coolant by squeezing the top hose before you started the engine, fill with coolant with the engine running and start looking for the leak.

[GeoffR]

Does the temp gauge rise slowly or does it just go from cold to the red zone without pausing in between? If it just goes from one extreme to the other I would suspect the temp sensor.

Under normal circumstances the engine will get hot and then open the thermostat, on earlier cars this would be accompanied by a dip on the temperature gauge. So if you start the engine and drive it a few blocks, does the radiator or top hose feel warm when the gauge is in the red? If the radiator and top hose are cold and the gauge is in the red it could be the thermostat or the sensor but even with the thermostat closed the engine doesn't normally get that hot that fast.

[Roxi]

Hi thank you . I believe I found the problem with overheating . the previous owner had used some sort of i want to say sealant im not sure but i took the thermostat out , it was like cement was all in the thermostat geez. I do have another problem that i think is real bad. I ran a scan with the obd2 the trouble code is u0100. Ive looked online and they say not to much hearing from the people on saab world i can understand alot better . thanks roxi

[GeoffR]

OK, that is interesting but I would still like you to answer the question on how the temperature gauge behaves please. It is possible that you have more than one fault.

Your fault code U0100 is incomplete, fault codes are normally in the format ANNNN NN where A is an alphabetic character and N is a number.
Fortunately U0100 has only one variant U0100 00 which translates as ECM missing on bus.
In English the ECM isn't talking to the rest of the car's systems on the data bus. ECM is the Engine Control Module. Unfortunately you cannot diagnose the problem without a Tech 11 diagnostic tool so you will need to find a workshop with the tool.

[Digger]

With this code the WIS tells you to wiggle cables, check wire connections, voltages and then troubleshoot using the Tech 2. With what you found plugging up your thermostat I suggest you look over both sides of your ECM for salvage yard markings before you jump into panic mode. There are part numbers and there are part numbers and even though the ECM has a part number for the unit, the paper label on the unit has a part number as programed for the specific car. An exact part number for the year, for the car can be swapped and work without being married to the network. It might not be by the book, but it will get you down the road. I don't know what, if any trouble this might cause later on as I have a Tech 2, I only tested this out of curiosity and did not make it my full time fix.

[RoccoH]

ECM always need to be married to the car so you can't simply swap it with one from the salvage yard. The ECM is locked with an immobilizer code and only for a specific VIN.

[swisssaabist]

seems the temp sensor at my opinion