[mitchntx]

Glenn has done tons of research on this and we are both about to the point of have custom machining done.

Autometer guages have a sending unit that is 1/8" NPT.
An LS1 motor has ports machined in, but are 12x1.5 metric.

Sure there are adaptors, but the wall is so thin the adaptors twist off with MINIMAL torque. And by that, not enough to crush a seal enough to prevent a leak.

Why don't they make a 12x1.5 sender?????

The stock sender ohms out WAY different ... almost 1K ohms lower than the AM.

[Cal]

I first tried the water pump location, but didn't like that because you don't get a temp reading until the T-stat opens

Elaborate on that a bit. Not sure I follow your reasoning.

I use a 160* thermostat and the guage begins reading at 140*. I can see the guage come up very slowly, not a jump all at once to 160*, as if the thermostat just opened.

Did I misunderstand something in your post?

My gauge starts a lot lower, at only 100*. Anyway, with the sensor in the water pump where I had it, the water apparently didn't circulate over the sensor until the T stat opened, then it did shoot up very quickly to 160. (I have a 160 deg T stat also.) With the sensor in the head, the temperature comes up smoothly. You really wouldn't see this problem with the stock gauge either since the stock sensor is also in the head. BTW, the metal is very thick in the location I used, so it was easy to get a tight fit. It's also a very accessible location, you just need to have the nerve to drill and tap the cylinder head.