5 quick operation and Maintenance Qs

Just for fun, I got another $4.00 thermostat and drilled a hole in it and popped it in, hoping some of the coolant would bypass anyway. Well... The gauge inside still reads 190ish.

...But the head near the sender unit reads 140-145 on the thermometer gun.

Before it read 170 and the gauge said 190.

I'm thinking the ground is way off, but I just added a huge ground strap to the gauge. Still the same. The thing is though - it starts at 100 in the morning, then gradually warms up to 180, then 195, then 210 on the freeway, it's not like it reads 195 by default so what's happening here?