temp sending question.

The hole you opened should work fine. It should be what is called 3/8" pipe. I believe the factory sender is 1/8" pipe so you need a 3/8 x 1/8" bushing.

You might break the other one if it's rusted bad. If you want to try, you'll have to determine what size it is, 3/8/ 5/16, etc. Sometimes you can buy a short piece of square keystock at a hardware store, and get a crescent wrench down close to the bottom.

Frankly, if it were me, I'd go with the one you got open.