So I have installed the reman'd head on my 4.0. I also installed a new temp switch.It was a little shorter than the one I took out.The threads on the old one are a bit boogered up.

On initial start up I let the jeep idle for like 10 minutes to check for leaks.

The tstat should have opened by that time.

Before installing the tstat I drilled 4 holes in it.One at 12 o'clock, one at 3 o'clock, one at 6 o'clock and one at 9 o'clock. I did this so I could fill the system with coolant and not have to worry about burping it. Could these bypass holes I drilled have anything to do with the temp gauge not readiing correctly?

Upon inspection fort leaks, there were none...in case. Someone wondered

 

The holes will greatly extend your t-stat opening time, if it lets it get warm enough to open at all. I always drill one 1/8 inch hole at 12 oclock on my personal stuff, but thats it.

 

Turns out the new sending unit could be bad. Remembered an old trick. Took the wire off the sender and installed a jumper wire from it to a good ground.Turned on the key and the gauge jumped to to 26+ with a quickness.Quickly turned off the key. Leaving the key on would have fried the gauge.

Results show the new temp switch I installed could be bad.If the gauge was culprit,it wouldn't have moved at all.