Hi, I had done bit of machining in high school machine shop years ago
and I enjoyed that. I even made several complex small parts to
replace broken parts out of metal by hand. but there's times I have to
have somebody do most of the process making the part I need since I
don't have a lathe!

Chewed up NPT thread hole in question is on top of water box that juts
out forward of this chyrsler 2.2L head. This hole either is used for
coolent temperature sensor or female hex plug, also for filling
coolent and purging air pockets. Same water box design on 2.5L. Go
and look at your 4 cyl caravans or K-cars btw for reference. Top of
water box is even with the valve cover sealing surface. On forward
surface is bored out for thermostat housing via two bolts & gasket.
The air heater coolent goes to this water box from below.

Access is easy and open.

The cast aluminum thickness for this damaged bore is appox 3/8 even
1/2 inch.

I have choices to repair this thread damage but I have questions for
each options and welcome your suggestions.

Oh, note that 2.2L head is still installed in the 1987 caravan and
don't prefer to take that head off at this time. The thermostat hole
is big enough for a finger to touch that NPT thread bore. Also I'll
prepare that area first by draining the coolent level below the water
box is easily done. Clean up area by chemical & grinding. Set up the
surrounding area to be protected with wet rags if soldering or welding
is required. I can stuff a piece of rag through thermostat's hole to
catch all the shavings.

Questions:

How can I get the info for this original NPT thread from a coolent
sensor's thread that I have? Plan: either obtain both NPT tap and
size drill or tell the machinist in making a plug adapter with the
original thread cut in center of this brass or aluminum plug.

Option 1.
Weld the hole smaller and redrill and tap it to original specs? (I'll
have that welding hire it done).

Option 2.
Plain plug with NPT thread in center for sensor (appox same depth as
thickness but kept from dropped through by a flange and fixed in place
by either aluminum soldering is doable with propane torch? or MIG
welding (I'll have this "hire it done" for MIG weld).

Option 3.
Have a machinist machine a threaded plug out of brass or aluminum with
standard thread with original male NPT thread in center for the sensor
or plug. Drill out the damaged hole & tap, use red loctite to lock it
in place. Use pipe tape or dope to seal the sensor's thread.

Note: Cannot simply weld that shut, this one is necessary for purging
air pockets in cooling system also sensor is used by that ancient
computer for emissions & also sets different timing schedules
depending on engine coolent temperature.

Thanks & Cheers,

Wizard (My real name is Jason Pero btw.)