Sig220

First the basics, 1996 XJ, 4dr, 4wd, 4.0. Just swapped a 98 block to replace the abused block the XJ came with. It has the simplistic dash with idiot lights, etc

On the original engine, the coolant temp sender was located on the rear of the cylinder head on the driver's side. Like the pic below........which was taken from Cruiser54's website (awesome site!)


When I swapped stuff from the old block over to the replacement block I plain forgot to check the head for a spot for the temp sender. I have installed the replacement engine and subsequently found where the temp sender hole would be is blocked by a allen head screw. I tried to remove it and have failed up to now. My question is: Where should I locate the coolant temp sender to? I saw this pic also taken from Cruiser54's website also (awesome site!) showing a different location, but it would have to be drilled and tapped on my block.


Any other ideas out there? The sender connects with just a single wire and uses the block for a ground.

Jim Malcolm

The temperature sensor with just the single wire installed in the had is only used for the gauge in the dash. The sensor that gets installed on the side of the engine block is used by the computer.

In later years, the gauge sensor is eliminated and just the computer sensor is used. It's also installed in the thermostat housing. My suggestion would be to get a thermostat housing for later model XJ and install the computer sensor there instead. The wiring may need to be extended.

On the thermostat housing, there is a nice flat spot where you can drill and tap for the gauge sensor to be installed. Wiring will certainly need to be extended. You can see the flat spot I'm referring to in some of the pictures on the below thread. I guess you could also tee the connection instead...

https://www.cherokeeforum.com/f2/4-0...-76310/index2/

Sig220

Jim,
My apology, I commented on your message this morning but must have forgot to hit the "reply" button. Anyway, thanks for the confirmation that the single wire temp sensor is for the idiot light in the dash. I knew they were different sensors but my intent was to move the single wire to the side of the block as the spot on the back of the head is plugged with a allen screw. I put a allen wrench on it this afternoon and it broke off in the head of the allen screw. I have a feeling that the previous owner loctited it in...or worse.

I checked your link you attached and thought about making a T fitting on the thermostat housing, but saw the comments saying "coolant in or coming from the head" is the hottest. While the temp at the thermostat may be 15 to 20 degrees cooler? My dash cluster is the simplistic one with just idiot lights, no tach so I really wanted at least a reliable warning light to keep me abreast of the engine temps. I may have to just install a separate temp gauge somewhere on the dash but still would have to find a spot in the water jacket.

I finished my check list on things to complete the job of getting the XJ road ready when I found the radiator is also leaking like it was shot with buckshot I will have a replacement here tomorrow, sometimes its seems the saga never ends!

On a positive note, I went by the u pull yard today and got a like new shifter handle, bezel and got a great shape bucket seat as well. All for less then $50. I will go back another day and get the passenger bucket seat as well was in a hurry today.

Almost forgot, here is a pic of the allen screw with the allen wrench broken off in it.

OutbackOz

so whats the one up the front then? I always thought that yes the rear one is for the temp gauge and the one at the front of the engine near the thermostat housing is for the pcm ? I have never seen one on the block?

bluejeep2001

On early 96...the one where your allen key is broken either feeds your temp gauge or runs the idiot light...depends whether you have a gauge or a light in your dash and you install either a sensor or a switch in the hole. The sensor in the the thermostat housing feeds the computer and is used for fuel scheduling and turns on the fan at the correct temp. On later 96 and up they just used the one sensor up front and let the computer drive the gauge. I think the picture of sensor in the block is a pre- 90's renix model. Does your model have a heater control valve or do the 2 heater hoses run directly into firewall

cruiser54

The one on the block is used on the Renix engines for the ECU. Renix has nothing in the thermostat housing. Only at the back of the head for the gauge.

Sig220

OutbackOz, my post may have confused you. I was using the pic of the sensor in the block to illustrate the question of where I could relocate the dash gauge sensor to as the normal spot is blocked by the PO putting in a allen screw.

Being that my XJ is a 96, I have the normal temp sender for the PCM in the thermostat housing, like this:


As XJ's 4.0 seem to be damaged the most by high temps, I am still looking for a place to get a signal for my idiot dash light. This is my sender and obviously it has no place to go right now!


bluejeep2001, my XJ still has the heater control valve which after 26 years looks really clean, I plan to leave it until I have a problem with it.

cruiser54, it is good to see you post in this thread! I guess it is not possible to splice into the wire from the thermostat temp sender to the PCM and connect it to the dash light? If I am right, I will have to make a "T" on the thermostat housing and run both senders from there, I guess. I really didn't want to make another hole in the block anyway!

On another front, the XJ is running although I might have a intake leak as the rpms are staying around 1100, I don't have any idea of the oil pressure (although the idiot dash light) has not lit up. Nor do I have an idea of the coolant temp for the same reason.........well and the sending unit is just hanging by the wire for now. I will have to play with my bluetooth OBD scanner to see if I can access some information I seek.

If anyone has any other idea besides making a "T" for the gauge sending unit on the thermostat housing, I am all ears and thanks for looking and posting.

cruiser54

DO NOT WAIT for the heater valve to fail!!!!

Sig220

If I could stick a temp sender for the dash instead of the heater valve being there it would have already been done! I am not going to forget about it, I just want to have some overheating safeguards in place before I move on to the "other things"

cruiser54

I mean don't wait for a failure of that valve. do it BEFORE it fails.

How about drilling and tapping the head for the sender? It's been done before.

Sig220

Any specific location you would suggest?

Here is a pic of the HCV that we are speaking about!

cruiser54

Same as the old head. Be aware that the surface has a slope to it.

Sig220

Cruiser, that pic in post #3 is my current head. Not only is at the rear of the head, the engine is installed making getting to it a hard proposition. Almost forgetting that that is a hardened allen screw with a hardened allen wrench in it! Too many chances to go off course drilling that thing out, I would think.

Is there another location or should I just lengthen the wire and make a T at the thermostat housing?

cruiser54

That might not be a bad idea. Use a tee that guarantees that the tip of the sender is well submerged into the path of the coolant.

Sig220

Will start looking around for what I need to make it work! Found out I didn't have a intake/vacuum leak causing the high idle, I had cleaned the IAC and throttle body and upon closer inspection the "idle screw" that should set the low rpm threshold was screwed in waaay too far. Backed it out and got the idle down to 850 before I quit for the day, will lower/fine tune it tomorrow. Replaced the drivers seat with a cloth bucket I got at the UPull yard and once it was cleaned, it is much more comfortable then the old vinyl (?) seat. I will head back to the yard tomorrow to grab the passenger seat and a few odds and ends. I am grabbing stuff out of 2000 that recently arrived....must have been setting for a good while, there were thorn bushes that had been cut growing up in the engine compartment that were bigger then the vacuum hoses!