96 xj thermo fans not coming on with temp increase

[Browneee]

Ok need some help.....

# My THERMO fan works ( comes on with A/C )

# Full radiator of coolant

# New water pump

# New radiator cap

# New radiator

Temp's rising and will sit just above 110' at hwy speed's, during stop starts it will rise a little higher then come downtown approx 110' again. Admittedly it's been 35'+ here in oz for last month or two.

While towing my boat (2200kgs) this morning (approx30') it sat at just above 110' with some stop starting. On the way home I had to pull into car wash to spray cold water on radiator till temp cooled down. When I finally arrived home I had to do the same thing, as I opened the bonnet I noticed the fan was not on ?, temp was very high and it should have been on.

Question...... HELP DIAGNOSE MY PROBLEM.... Temp switch stuffed ? Or relay stuffed ?

Regards Rob

[Roler]

Temp of 110 seems a bit generous. The fan works you say, since it comes on with the A/C. Verification of the correct temp would be a first step, to see if the gauge is actually giving you the correct temp. Make sure all connections are good. If temp inaccurate, replace temp sending unit and check again.

[rainman]

1. check for codes.

if the fan comes on with the ac then the relay/ fuse ect is all good.
as it is a 96 check to see if there is a temp sender, going into the head, back passenger side. if there is it means that that the dash temp gauge is independent of the temp gauge that the pcm uses.
it may be that the dash gauge is reading 110* but the pcm is not getting 105* yet and the PCM is waiting for it to get hotter before switching on the fan.

check connections & wires going to the temp sender in the thermostat housing (for the PCM). pull sender and check resistance values, in the FSM.

have you got some way of getting a temp reading at the thermostat housing to check that the dash gauge is reading correct?

[Roler]

Originally Posted by rainman

...
have you got some way of getting a temp reading at the thermostat housing to check that the dash gauge is reading correct?

Thats what I suggest as well. See above. Sounds a bit like sending unit issue?

[rainman]

could be I can never remember when they went from using a separate sender for PCM and dash to using just one. it was either post update or obd2 that they went to the 1 sender.

[Browneee]

Thanks for quick replies guys, much appreciated....

Before I go searching a back of engine (pain in the ass to get to) screwed into the thermostat housing up front is a probe of some sorts ? Would that be the temp sender ? .

Just to clarify, yes my fan comes on With the aircon.

[genericuser]

Originally Posted by Browneee

Thanks for quick replies guys, much appreciated....

Before I go searching a back of engine (pain in the ass to get to) screwed into the thermostat housing up front is a probe of some sorts ? Would that be the temp sender ? .

Just to clarify, yes my fan comes on With the aircon.

Yes! That is a thermal sensor. If you have a multimeter you can test it. Remove and test it cold then boil some water and place the sensor part in the water, leave for awhile then test again. Use OHM setting and set to 200.

Cold you will get 0 ( zero )
Hot around 200 or so.

Compare to the specs in factory service manual, to see whether it is okay.

My thermal sensor was toast. 0 at both cold and hot.

I also had another problem from a PO. A Bosch relay was used in place of the original relay. Which had a different pin out ( pin 87 and 87A were switched ) which caused the thermo fan to run all the time. I pulled a relay out of an explorer which had the same pin out as the jeep relays and it works fine now.