XJ ? Temp sensor

[Brett]

1989 Cherokee XJ, 4.0l blah blah

Open 91+ cooling system, with new style thermostat housing with the provision for a temp sensor. New 3 core open style radiator does NOT have the stock provision for the temp sensor that would activate the electric fan.

So, the question is, does anyone know of a sensor that I can use in the new thermostat housing, that will communicate with the older Renix computer? Would a stock sensor from a '91+ work? ideas? thoughts? bash me?

GO!

 

[I Lean]

What's your issue--turning on the fan? Wire it so it's on with the ignition. Done.

 

[Brett]

What's your issue--turning on the fan? Wire it so it's on with the ignition. Done.

I like to make things difficult!

 

[Brett]

Oh, and thanks for the round black rubber thingy, it worked great. And thanks for the long silver greasy metal parts as well!

 

[Badger]

so the rad doesn't have a bung for a temp gauge? where did you get the rad from?

 

[Brett]

so the rad doesn't have a bung for a temp gauge? where did you get the rad from?

State Radiator.....it's for a 91+ though.

 

[Badger]

i know NAPA sells 3 cores as well you might have been able to get a 3 with the temp bung ,maybe..............

i'm pretty sure the stock rad for my 95 had one for a secondary temp gauge.

the only thing i could see doing is either tap a second port on the thermostat housing or put a "T" on it and and have both sensors on that

 

[Brett]

i know NAPA sells 3 cores as well you might have been able to get a 3 with the temp bung ,maybe..............

i'm pretty sure the stock rad for my 95 had one for a secondary temp gauge.

the only thing i could see doing is either tap a second port on the thermostat housing or put a "T" on it and and have both sensors on that

From what I was told, the '91+ used the thermostat housing sensor for the fan, since it registered the correct temp of the coolant, instead of the "cooled" coolant exiting the radiator. Anyway, as for the housing.....I'd rather not have to tap a new hole into just for the sensor (especially if it was the original sensor from the radiator, since that was huge). I'd prefer to find one that would just work in the hole that's there and also that would communicate with the computer properly.

That or I'm doing a switch

 

[Badger]

you are looking at a switch then .there shouldn't be a temp gauge that would do what your asking.the renix had two sensors right? so the computer of the renix is looking for two separate inputs.you could try splicing the two together to get two signals out of one sensor but chances are that won't work and it will only raise the resistance on the line causing a false reading or possible shorting out and taking the computer with it.

another though you might be able to put a "T" fitting on the heater hose line going to the heater core since that also comes out of the thermostat housing

 

[DaveB]

I just went out and looked at my son's 87 mj and there isn't a temp sender in the radiator. His motor has the one in the rear of the head which is used to run the temp gauge in the dash. On the 91-95 motors the dash gauge sender does not go to the computer at all it just runs the gauge and I would guess the Renix system does the same thing. On some of these motors I've seen a sensor down below the exhaust manifold and above the knock sensor that is screwed into the block's water jacket and that may be a spot where you could mount your sensor. Why can't you mount the sensor in the new thermostat housing like the 91+ motors do ?

 

[Badger]

dang you actually have me remembering know.the one in the Tstat housing does run the fan and there is one one the back drivers side of the head that did the dash gauge.the one on the back of the head should be sending the temp to the computer the one on the housing just works the fan.thats how it works on a 91+ but i don't know if the renix is the same way

sorry Brett my head wasn't screwed on straight last night i guess.

 

[DaveB]

dang you actually have me remembering know.the one in the Tstat housing does run the fan and there is one one the back drivers side of the head that did the dash gauge.the one on the back of the head should be sending the temp to the computer the one on the housing just works the fan.thats how it works on a 91+ but i don't know if the renix is the same way

sorry Brett my head wasn't screwed on straight last night i guess.

On the 91-95 xjs the sending unit in the back of the head doesn't go to the computer at all, just the gauge. The one in the thermostat housing does go to the computer and controls the fan. On the 96+ there isn't a rear sending unit since the computer also runs the gauges. When I built my scrambler, which has a 99 4.0 and a 93 xj wiring system, I had to blend the wiring from the 93 to the old 84 cj gauges and studied the schematics to make sure I did it right.

 

[Badger]

then you are the one to talk to.

 

[Brett]

Why can't you mount the sensor in the new thermostat housing like the 91+ motors do ?

The stock sensor that was on the radiator is about 3 times bigger than the sensor that would go in the thermostat housing. So, dunno what to do. I used a stand alone system before that would just kick the fan on with a temp sensor, but I'd rather the AC still be able to turn it on as well.


I'm screwed!

 

[DaveB]

You can measure the old sensor to see if it is a thermostatic switch or a resistive type sensor. Once you know what type it is you might be able to find a newer style sensor that could replace the old one. You could also go back to the older radiator and still leave the system open like I did on my son's mj by using an upper radiator hose fill spout.

 

[Brett]

You can measure the old sensor to see if it is a thermostatic switch or a resistive type sensor. Once you know what type it is you might be able to find a newer style sensor that could replace the old one. You could also go back to the older radiator and still leave the system open like I did on my son's mj by using an upper radiator hose fill spout.

Now....where did I leave that old sensor? I think it's in my tool box. How would one go about checking to see which type it is? As for the radiator, I don't want to switch back to the old style. Spent too much on this three core

 

[DaveB]

Now....where did I leave that old sensor? I think it's in my tool box. How would one go about checking to see which type it is? As for the radiator, I don't want to switch back to the old style. Spent too much on this three core

The thermostatic switch type will read open when cold and 0 ohms when hot (normally open) or opposite if normally closed. The resistive type will read something like 8k ohms cold and less as it heats up. If you need a good meter to check it stop on by.