nosfedgta

Hey I have a problem. I have a 96 XJ and just recently put a new motor and trans in it. The new motor is a late 98 and it did not have the hole in the back of the head for the coolant sensor for the guage. Everything else was good though. The electric fan was coming on when it reached temp and would shut off etc. Well Today I got around to solving my problem of not having a guage. I put a brass T in the hole where the coolant sensor was and then installed the coolant sensor and the coolant temp sensor. Well the guage started working, but now my fan wont come on. I let the temp get to 240 and it still would not come on. Well I took the t off and put it back the way it was originally and that didn't work either. So now I have no electric fan and cant figure out what happ...

any ideas? did the sensor just decide to take a crap ? it was the original that was in my old motor and had 254k on it.

is there a way to test the sensor?

drew

DFlintstone

96 is a transition year. 97 has that stuff on the T-stat housing. Not sure of your answer, but you might look at a 97 at the JY and see if that helps.

djb383

Are the tips of both the gauge sending unit AND coolant sensor in a good steady flow of coolant using a "T"? I'm not sure how they can be.

How does it get to 240* in this weather/this time of year?????? Has the belt driven fan been removed? Did u check the efan fuse/relay? Sensor could have been broken electrically.

DFlintstone

I'm curious which hole got the "t", but Djb is your guy here.

nosfedgta

The hole in the tstat where the coolant sensor is located. I put a t there and added the temp sensor.. the guage is working perfect.. but now the fan won't come on.. now if I turn the ac on the fan comes on perfectly..

djb383

U say the gauge is working "perfect" however, how "perfect" it is working is questionable. Both the temp sending unit and coolant temp sensor are located by the Factory in a stream of flowing coolant, not in a "T" that has stagnant coolant/trapped air in it.

Again, I'd suspect a bad electrical connection at/in/thru the coolant temp sensor. Efan on when the compressor engages is the Factory default and has nothing to do with the coolant temp sensor.

nosfedgta

Now I'm really confused.. i replaced the sensor today.. well when I unplug the sensor the fan comes on.. plug it back in and it shuts off.. what the heck man.. i just wanna drive my jeep... fuse and relay are both good... i dont get it

ehall

The value on the gauge might be way off. Get an infrared temperature gun and hit the thermostat housing to see

djb383

That is the factory default......it's a safety feature to prevent overheating. Better to have the efan on constant if the wire/plug comes off than have the efan totally disabled due to the wire/plug falling off.

DFlintstone

Agreed with all above ^. I'm not sure how yours works, but a couple things....sometimes a relay might close and make a circuit with a sensor "open". It can work ether way. Secondly, the E-fan will not come on until it's really hot, like up over 215*. Going slow, (with next to no airspeed), up a hill might get the system hot enough to trigger it for instance. It might usually stay off, until the "auxilary" fan is needed. Some guys run without them. Because I do a 3 mile gravel hill climb whenever I leave home, I need mine. Btw the fan shroud is important as well, if you want your main fan sucking air through the rad.