What is this hole for?

Wow, while trying to figure out a title for this thread, I realized that I couldn't word it without it sounding kinda funny.

Well I finished up (almost) everything with installing the new head on me '01. I got the head from Odessa, and there appears to be an extra hole at the back drivers side on the top of the head. It's a fine thread, maybe about 5/16" or 1/4", but I have no idea what it's for. Wasn't there a sensor somewhere around here on some XJ's? If so, is this what the hole is for? Please excuse the crappy pic, but I can't find my p&s and all I had was the iphone on me. For reference, the head bolt you see there is the #14 bolt, driver's side rear.

If it was for a sensor, anyone know what the proper thread count is so I can plug it?

Coolnt temperature switch. Sorry unsure of thread size/pitch.

And this usually isn't in an 0331 head, right? I swear I can't remember pulling anything like this out of the original head, and there were no extra parts when putting everything back in.

Just grab a temperature gauge/idiot light sending unit for a 95 4.0 engine.

joe_peters said:

Just grab a temperature gauge/idiot light sending unit for a 95 4.0 engine.

Click to expand...

Is it called anything specific or is it just the coolant temp sensor?

Should just be the coolant temp sending unit

They may want to call it most anything at the parts store.

The coolant temperature sensor--CTS--is in the thermostat housing. It provides data to the PCM.

You want the sending unit for the instrument panel temperature gauge or idiot light--doesn't matter which because you aren't going to hook anything up to it.

The 96 or 97 up 4.0s use a combination CTS in the thermostat housing, the information for the gauge or idiot light comes from the PCM, not directly from the sensor.

Good luck.

Question: Does that sensor go in at a bit of an angle?

I got a brass plug that is 1/8 pipe thread at Napa. I looked at the sensor and the threads and size match, but the sensor was $32. The plug threads in by hand at least 3 to 4 full rotations but it is at a bit of an angle. It looks like it may be angled on purpose because of how close the hole is to the valve cover.

Anyone?

Just put some thread sealant on it and put it in. Shouldn't leak if your able to get 3-4 full turns on it.

mine are older heads, but all of them (Renix and H.O.) are straight up/down.

alright, we'll see if it works.

ask for "temp. sending unit" for a gauge on the dash for a '96 4.0L-- you'll get this for about ten bones and it'll fit.

BWD Coolant Temperature Sensor

Part No. WT430

Warranty: 1 YEAR REPLACEMENT IF DEFECTIVE
Temperature Sender - With Gauge

$10.39

BWD Coolant Temperature Sensor

Well, I just put that plug in there with some thread sealant and it worked fine. Took it to get gas, about a 5 mile drive, checked the fluids, and all is good.

:yelclap::yelclap:

I just hope that the jeep doesn't find out I just got paid, or else it will break again, haha.

01_XJ said:

Question: Does that sensor go in at a bit of an angle?

I got a brass plug that is 1/8 pipe thread at Napa. I looked at the sensor and the threads and size match, but the sensor was $32. The plug threads in by hand at least 3 to 4 full rotations but it is at a bit of an angle. It looks like it may be angled on purpose because of how close the hole is to the valve cover.

Click to expand...

I just put a NPT plug in there when I swapped my 99 head to a 95 head.

joe_peters said:

They may want to call it most anything at the parts store.

The coolant temperature sensor--CTS--is in the thermostat housing. It provides data to the PCM.

You want the sending unit for the instrument panel temperature gauge or idiot light--doesn't matter which because you aren't going to hook anything up to it.

The 96 or 97 up 4.0s use a combination CTS in the thermostat housing, the information for the gauge or idiot light comes from the PCM, not directly from the sensor.

Good luck.

Click to expand...

For future reference - 97 up. 96 uses the old style gauge cluster with individual signal lines for each gauge even though it's OBD II. Gotta love multi-year design changeovers...

01_XJ said:

Question: Does that sensor go in at a bit of an angle?

I got a brass plug that is 1/8 pipe thread at Napa. I looked at the sensor and the threads and size match, but the sensor was $32. The plug threads in by hand at least 3 to 4 full rotations but it is at a bit of an angle. It looks like it may be angled on purpose because of how close the hole is to the valve cover.

Click to expand...

Straight in on my 96, like the rest of the guys said. Heard multiple people say an NPT plug worked fine, so I'd just dump some plumber's dope on it and screw it on in.

As a side note that sender (or plug) makes for a great way to burp the air out of the cooling system while doing a flush.

should be 1/8 NPT thread (NPT is tapered wall)

It's in and working fine with some of the white thread sealant on it.