siglincasey

My experienced friend and I rebuilt my jeeps engine. We ended up using a head off a 97, the original head was a 94 -95. On the back right corner there is some type of sensor that threads into the(94-95) head into where the water goes. Looks like a nut. The 97 head doesn't have it, so before its drilled and tapped can some tell me what it is and what's it for?

red4dr

temp sensor for the ecu i believe

cruiser54

Temp sender for the gauge. Pipe thread. 1/4" IIRC.

5-90

That would be the temperature sensor to drive the gage in the IP - drill & tap 1/8" NPT, in the same location (recommend you centre drill - or at least a good centre punch and pilot hole - before you drill it out for real!)

Use never-seez on the screw threads, tighten finger tight, then an additional 1/4- to 1/3-turn with a wrench (you should not need more than that.)

The sensor for the ECU is found in the thermostat housing, it generates a signal for the ECU's reference, and for the ECU to energize the fan relay.

This sensor was omitted for OBD-II, and the IP gage is driven by the CAN bus instead (OBD-II data stream) I do not believe the water passage in the head was altered, merely that the boss went unmachined.

EDIT - Cruiser seems to think it's 1/4" NPT, but I'm pretty sure it's 1/8" NPT. To make sure, take the sensor with you when you go to get the drill & tap - stop off in plumbing and thread the sensor into a union of each size. It will only fit one - please confirm once you have done so, for the rest of the class...

cruiser54

Could be. That's why I typed IIRC!! Hmm. Not so sure now. Isn't the oil sender 1/8" NPT and the temp sender 1/4" NPT? I don't feel like pulling down the ladder to the garage attic and verifying right now. For some reason, my balance might be off this time of night........

belvedere

cruiser54

I survived the trek up there. 1/8" NPT on oil sender and temp sender. CTS and IAT are 1/4" NPT.

RTorrez1

It would be easier just get a new t-stat housing and put it in there since that's where the later models (97-01) have them. You can get a new housing that already has the threaded hole. I know that a few people on here have done this.

5-90

That was done 1991-up.

1987-1990 had three temperature sensor - driver's side of the block (behind the exhaust, for the ECU, M20-1.5 straight thread, I think - a Peugeot or Renault part also fits there with lower operating temperatures,) driver's side radiator tank (thermal fan switch, 3/8" NPT, I think) and driver's side rear of cylinder head (IP gage, 1/8" NPT.)

1991-1995 had two: the driver's side rear of the cylinder head (for the IP gage,) and the other two were combined into a single sensor in the thermostat housing (threaded 3/8" NPT.)

1996-up (OBD-II) rigs have a single sensor - in the thermostat housing.

Therefore, he should already have the later thermostat housing.

Also, the upper rear of the cylinder head is pretty much the hottest part of the cooling jacket - it's a sort of "flow pocket," and has a reduced flow rate for coolant. If you move the sensor to the front of the head (better coolant flow,) you'll wan to keep a better eye on it, since it won't tell you what the "hot-spot" temperature is. I prefer having the sensor at the rear of the head, since that will tell me much sooner if the engine is overheating!

cruiser54

CTS on the block, for the ECU, is 1/4" NPT. Radiator sensor is metric.

5-90

Ah - thanks for that. Most of the CTS units I've seen (in general) were 3/8" NPT, and I hadn't had an XJ one out yet.

Do you happen to know the threading on the RENIX drain plug? I want to put an elbow and a cable-operated valve in there in my refit, I just haven't had one out yet (I already know it's a 5/16" square drive to get the thing out - you can easily make a tool to do the job with a 5/16" or 8m/m cheap-O hex key and a grinder in about five minutes.)

cruiser54

I believe the block drain plugs are 1/4" NPT but with a 5/16 square drive.

siglincasey

To give you all a better idea

cruiser54

Yep. That's it.

Remove the remnants and put a 1/8" pipe plug in it's place.