What is this hole on the cylinder head of this 97 Wrangler for?

Hi everyone. First time poster.

Helping an older neighbor swap head on 4.0 97 Wrangler. We're in the very final stages of reassembling everything and ran into a problem.

Can someone tell me what this hole in the head behind the alignment dowel on drivers side is for? It looks like it was a stud for a ground strap that went there before, but the stud in question won't thread in and we're also getting coolant that's coming up out of it as well. None of the diagrams that I've looked at or videos show what it is. At a minimum I wanted to confirm the thread size and proper bolt that is supposed to be there before I start tapping / cleaning threads.

Thx in advance...


ps the ground strap and big bolt in Pic are currently on that rear headstud just for now, but were not there before.

Wow - thanks everyone for the prompt replies.

This helped a ton, and now confirms my suspicion that this engine had some overhaul/possible year mismatch happening. Neighbor bought it 1 year ago and it ran fine until it overheated - otherwise stellar condition. It is definitely a 97 per all paperwork - but now we know it has a 95 (0630) head.

The previous owner had a noN-NPT threaded stud holding the ground strap down in that hole ( see pic). I grabbed an old 1/8 NPT temp sensor from an 80's Chevy s10 that had a long shank and with some good threadlocker it sealed up nicely.

We tried to use a smaller / cleaner looking pipe plug but the upper threads in the head been ovaled/worn down by the stud that was in there, so we need something longer to make good contact into the lower/deeper threads. The old sensor was also helpful as it was taller and let us get a socket on it to tighten up. The smaller plugs were too short and didnt give enough clearance with the edge of the valve cover to do much. Will probably just leave the sensor in for now.

First time tearing down and rebuilding anything in a Jeep for both us, and lots of interesting quirks (we are both seasoned Chevy/SBC gearheads). This forum helped us out of several hairy but common issues. Much apopreciated.


JT