[tucsonjwt]

I put a 180 degree thermostat in my 83 454 and it stays at a constant 180 or less on the gauge. That is with a stock setup and in 110 degree AZ temps. A fluctuating temp gauge means that the sensor may be faulty - cheap replacement for a guess - I would look for AC Delco or GM sensor if you can find it. Also, it might just be loose wiring - I would check that first. Try to use a digital temp gauge and shoot it at different areas on the engine, especially near the temp sensor.