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Engine Temp still reads low after replacing thermostat

487 views 3 replies 4 participants last post by  BobSaabit 
#1 ·
So, recently I replaced the thermostat since my engine barely reached half way temperature and was going up and down a lot.

Now with the thermostat replaced, it reaches halfway on idle in about 10 min and a tiny bit above halfway when driving for 5-10 min. But when it's reaches halfway, it quickly drops down to about 1/4th of the gauge.

And then randomly it goes back up to a little over halfway, and can stay there for about 5 min after dropping again depending on driving speed.

Any ideas what it could be? I had a 89 degree thermostat and replaced it with a new 89 degree one.

Could it be the gauge itself?
 
#3 ·
You can check the wiring to the temp sensor. For the gauge, it's in the side of the head, above the transmission, close to the lines to the heater. The wiring can flex and come out of the sensor. That happened to me. You can also use an ODB II reader to see what the other temp sensor is seeing, I believe that ODB gives you the ECU temp sensor (yes, there are two).

However, your symptoms don't really sound like a bad gauge.

I replace the thermostat with an aftermarket 89º thermostat, and the temp gauge would still barely make it halfway, and drop when on the highway, even in summer. A Saab OEM thermostat fixed that issue. Note, both were made by Motorad!
 
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