Topic: Temperature sending units on YJ's vs tJ's

[SDWE61988]

Hello everyone,

I have recently swapped my engine my 95YJ with an engine froma 97 TJ that I just picked up.   I was hooking up the wiring harnass last night and found out that there is not a temperature sending unit for my temperature gauge on the head of the 97 TJ engine.  The YJ had the sending unit on the top left rear of the head.  I do not have much experience with TJ engines.  Was the temp gauge/ sending unit an option on TJ's or do I need to splice into the wiring of the the sending unit for the computer?  Any help on this would be appreciated.

[lanulos89]

i did the swap the opposite way you did.  the tj gets its temp from the main temp sensor.  so splice it in.  btw just a side note you lost 1hp,  the tj engine has 1 less hp than the yj engine.

[Jeffy]

i did the swap the opposite way you did.  the tj gets its temp from the main temp sensor.  so splice it in.  btw just a side note you lost 1hp,  the tj engine has 1 less hp than the yj engine.

Actually, it's 3hp.  But it makes it up with a bit more torque, IIRC.

[lanulos89]

even better    (for me at least)

[sharpxmen]

I am not 100% on this so just take it as a concern - i dont think the PCM and the gauge sending units are the same, plus if you splice in the PCM one i think it might send the wrong info to it (since the gauge has a 12v power there will be a voltage on the sending unit resulting from this, not sure what the impedance of the gauge is but depending on that is how much it would affect the PCM reading). it might work but in my opinion I would look for a way add the original one to the header or engine (even if it won't affect the PCM i don't think the reading on your gauge would be accurate). You could in fact use a multimeter and measure the ohm value of both sending units (old one and the new PCM one at the same temperature, so don't hold them in your hand) and see if the reading is the same, if it isn't then it ain't going to work.

[lanulos89]

drill and tap a freeze out plug?  there is one on the back of the head and its pretty close to where that sensor is if i recall correctly

[SDWE61988]

Thanks for the advice.  I was afraid of that.  I will have to pull the sensors and test them.  They are thermisters correct?  They look like them anyway.  I am not sure if I want to go to the trouble and risk of drilling into the head for that.  THat sucks about the Hp loss.  I added a banks header to this engine so hopefully with that, a 4.0 TB, and exhaust, I can recover a couple of those hp. who knows.  Maybe next year when I get some money saved up again I can do the electric fan conversion.

[lanulos89]

go pick up a replacement freezeout plug drill a hole and nut and bolt it seal it up nice then just replace one on you head and extend the wire, the gauge will be off a litlle but for the most part will be accurate enough

[jdarg]

I ran aftermarket gauges in my old TJ because the computer controlled ones basically lie.

For the temp gauge I cut the host to the heater core in half, put a brass T in there, and used the center of the T for the temp sensor. You need to make sure the sensor sticks down into the middle of the hose - if it doesn't go down far enough it will always read much cooler.

You also might be able to drill+tap another sensor hole into your thermostat housing. There seems to be plenty of room for that.