The Thunderbird/ Cougar temperature sensor has a 5/8-18" thread. According to common machining practice the minimum thread engagement for a 5/8" threaded connection is 7/16". The stock housing is not thick enough to accept this thread connection. If you tap in a 5/8" connection it will have a high chance of leaking.
To start the project I took a 1" diameter by 5/8" thick aluminum disk and had it welded it to the housing as shown. Of course I had my local Aluminum welding expert (Eric at best Welding in Naugatuck, CT) do the welding. As usual the weld is excellent. The reason for the 1/4" hole is because Eric cut the disk with a hole saw.
Next I took it to a drill press leveled the top of the part and drilled out a 37/64" diameter hole. This will give me at least 75% of threads with the tap. I had a hard time hitting the center of the hole. This was because I used a drill press that did not have a angled table. After I was done, some smart allec informed me that there was one in the other building. Bummer...
Next I tapped out the hole with a 5/8"-18 tap.
Here is a top view of the housing. This puppy will not leak!
Here is a view from the bottom. Total cost about $100. excluding my labor. Some of you may ask why, because my new intake has two temperature sensors. Well, I wanted to do it!