Incorrect ECT readings on 5.3 swap

[llafro]

I was working on tuning a 5.3 L33 swap in an 87 Trans Am. We replaced the coolant temperature sensor in the driver-side head with a new one that should have been correct for the harness and PCM. The wiring is not damaged that I can see. I see ECT readings in the scanner that don't match with reality. The engine block was warm, but not hot, but the sensor is saying 240-250 degrees. It's clearly reading incorrectly, but I don't have a mechanical gauge in order to see what the actual temperature is. Any ideas on what might be wrong? I was wondering if the ohm range on the sender might be incorrect. Did GM use different ranges at some point?

This is an L33 (aluminum block) 5.3 with a 2000 Camaro PCM and harness.

[5FDP]

Could even be a bad new sensor.

[brianmcb]

I used a sensor for a 98 camaro on my L33 swap. It's a 3 wire sensor so I could run to the stock gauge in my dash. Your sensor may be faulty, or wired backwards maybe

[brianmcb]

Or maybe it is reading correct and you have a steam pocket in the system? Try burping the rad