I bought an aftermarket temp sender from the parts store and my gauge was showing about 30 degrees hotter than it should have been. After doing hours of research, I found that the tolerance on aftermarket senders is really poor. I went on a mission to find the correct part # with a "spade" style connector, I purchased an AC Delco D1885 off Ebay. The gauge is now very accurate. I have a 1989 GTA.

This is the sensor on the driver's head between cylinder 1 and 3.

 

How are you determining the gauge reading? On my 89 there is a 100 deg tick and a 220 tick. There is a tickmark half way between but i have since learned by monitoring temp via laser temp gun and ecm logging that the halfway mark is closer to 185-190 it seems. Not 160 as you would think. At 220 my oem temp sender is spot on. Just my observation but this looks like a nice part to try. I could use a new sender

 

My old sender was showing 240 gauge when the actual temp was around 200.

I know actual temp because I have an Accel DFI and it has its own sensors.

To test the new sender I let the car warm up to 220 by keeping the fans off, and the dash gauge also was reading 220.

I agree with you that the half way point between 100 and 220 is more like 185-190.

I prefer the spade connector because I have headers and this keeps the wire away from them better.