I just put a new Temperature sender sensor and now the temperature gauge starts in the middle when the engine is cold. Any idea on what I did wrong?

 

The coolant temp sensor to gauge is a super simple setup.

The sensor changes resistance with temperature.
The gauge measures resistance and shows what it is via the needle.

• Either the sensor is broken.
• It's the wrong one
• or the gauge is broken.

Could be a broken wire, but normally that would make the gauge show either full hot or full cold.

 

A high reading can be caused by poor grounding.

Is this an NB? If so borrow a scangauge or ECU scanner/reader and see what the ECU water temp is. If the ECU reads normal than it is likely bad grounding of the sensor threads. The gauge feed grounds through the threads so if you used a heap of tape on the threads (you shouldn't use tape) this can cause a bad/poor grounding.