This problem has been discussed but I have not found a specific reference to this symptom. 2008, 2.4L, 5 Spd, 215K mi. The temp gauge reads normal then drops instantly to 0/cold. It can jump to normal temp instantly from 0/low. Sometimes it will read correctly during warm up, sometimes it will stay low. The change is instant either direction. I have 27 ASE certs and have been "wrenching" for 50+ years. New sending unit. This is NOT a thermostat issue. I suspect intermittent wire failure/opens. Has anyone else seen this symptom?

 

Is the coolant full? In the tank and under the pressure cap.
What happened just before this started? Dexcool change?
How old is the Dexcool? It has a 5 year shelf life, no matter how many miles.

 

Possibly an air pocket , more plausible a loose connection check for loose pins in the harness connector. I had to replace the pigtail on mine last year.

 

Yup. All the normal things are OK. None of the system related factors can cause an instant gauge change. Quite familiar with air pockets, coolant change, and the like. Had a repair shop for many years. Looking for wiring issues and thot there might be a "problem area" (such as a pinch-point in the harness) that you guys have found that might direct me when I really "dig in" to this one.

 

That sounds more like loss of signal than anything else. Did you check the wiring at all?