Originally Posted by Geo Jeep
Wow the needle doesn't move past half until 107 deg! Can I confirm that is correct? Living in Darwin my temp gauge needle spends quite a bit of time above halfway.
Yes I have an auto........
Invest in a OBD2 reader. It's the only way to properly monitor the engines vitals in realtime (and read and clear any engine codes etc). You could also install a proper coolant gauge, but this is more work and potentially more cost, and you won't have the benefits of being able to do everything else a OBD2 reader can.
All vehicles since about 1990 have very vague coolant gauges. Coolant temps fluctuate a lot so manufacturers wanted to dumb their gauges down to only basically say cold, normal, and hot.
There are many OBD2 readers out there, scangauge is very popular. My personal preference is a OBD2 bluetooth transmitter (eBay $5-15) which is permantly plugged into my OBD2 port under the dash, which then reads the ECU and transmits the data to my Android phone via bluetooth. To make sense of this data I use a app on my phone called Torque (Google Play store $0-15) and I can monitor every single sensor on the motor, which includes the coolant temp sensor.
I am always driving around with one eye on the engine's vitals. You soon learn what is normal what is not, and how your vehicle reacts to different conditions etc.
General consensus is that coolant temps of 107+ degrees for a prolonged period of time is no good. And like I said, if yours is auto, it is very likely that your auto trans fluid is getting too hot as well.
If you have a 2010+ JK, you will be able to monitor trans fluid temps as well via the OBD2 port, early models didn't have this provision.