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]

...
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]

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.

[Browneee]

Update....

This has been bothering me ever since I wrote this thread.....

I just went out side and run the jeep in idle up to temp to see and take note of what's going on from the gauges point of view. Current temp out side 28' Celsius no breeze . Air-conditioning OFF.

Assuming the temp gauge is correct ( I found it on back left corner of engine as viewed from drivers seat ) . And going off the markings on the gauge 40-70-100-112.5-125 degrees. This is what I found.

Car idled up to approx 90' within a few minutes. Then took approx ten minutes max to idle temp up to approx 110' where I heard the fan come on :-) . Fan stayed on long enough to bring temp down to approx 106' (which was not very long, matter of seconds) . I watched it do this a couple of times just to make sure the fan came on every time. So the temp fluctuated between 106' - 110' at idle.

Then I turned the air-con on, the temp was on its way up to approx 110' when I turned it on and this time the fan kept running until the temp dropped to approx 103/104' and then began to cycle on (14sec's) and off (5sec's) maintaining the temp at 103/104' and then over approx 5/10 minutes further reduced temp to approx 101' until I was satisfied it was working.

So again on today.... I checked the temp , it's reckons it got to 38' (yeah it was bloody hot that why I was out on my boat) . Yes I know my boat drive away is 2200kgs which is at the very top end of what my jeeps rated at 2268kgs. Yes there was a lot of stop starting with traffic on the way to the river and on way home. The Jeep is mostly stock apart from suspension which has been upgraded to take the extra weight of towing boat and adding break controller. Apart from that she's stock.... Stock size wheels & tyres etc.

I do want to add a heavy duty tranny cooler to replace the stock Ozzie addition because the design is shit ;-) but that's about it.

So all in all any of you reading this again you honest opinions/thoughts/technical experience on what I discovered would be appreciated.

[Browneee]

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.

Ok so I've got the probe in front (thermostat housing) and one at back left corner (assuming that's the temp sender to gauge?) . The one up front is that the one for adjusting fuel/air ratio in the computer ?

[kyphonii]

My 96 will never make temp close to 105 by idling, the temp the aux fan comes on.
You have another issue if you get high temps at idle, mine will not get close to 100 on the highway.

[Dustbowl]

Sounds much like the thermostat has jammed itself shut, because with both fans running you can not get it below 100... At highway speed the fans won't be doing much at all.

[rainman]

so the one up front is what the computer uses.
looks pretty much normal to me, it is all doing what it is supposed to. Except that it is all happening about 5*c hotter than ideal.
Suggests to me a instrumentation/ sender problem.
again see if you can measure the temp at the thermostat housing & compare to dash gauge.
alternatively if you can get a scanner you can read the engine temp and check against the dash, as well as verifying at what temp the computer is turning the fan on at.
They are cheap and very handy for chasing problems and work in many different cars. Suggest something with a elm327 chip in it.
http://www.ebay.com.au/sch/i.html?_trksid=p5197.m570.l1313&_nkw=elm+327&_sacat=0&_from=R40

[Browneee]

Sounds much like the thermostat has jammed itself shut, because with both fans running you can not get it below 100... At highway speed the fans won't be doing much at all.

Am I correct if the top hose gets hot the thermostat is working ? Pressure builds up in top hose and it gets hot. While driving to & from work today the temp never rose above 90 at speed. At traffic lights rose to approx 101 then came straight back down when moving again. However outside air temp was a nice & cool 25 ....

[Windex]

It sounds like you have what I have, my dash reads a bit higher than expected. I am suspecting that it is something within the cluster so it is sitting in the 'too hard' basket at the moment.

Temperature gauge diagnosis (http://www.ausjeepoffroad.com/forum/showthread.php?t=119696)

[carvesdodo]

Am I correct if the top hose gets hot the thermostat is working ? Pressure builds up in top hose and it gets hot. While driving to & from work today the temp never rose above 90 at speed. At traffic lights rose to approx 101 then came straight back down when moving again. However outside air temp was a nice & cool 25 ....


Verifying the the gauge and computer are seeing the same temps, as the others mentioned is probably first thing to do.

A tired fanclutch is a common cause of increased temps at idle/slow speed.

Thermostat only controls flow to the rad ... heater hose should be getting its flow from the t'stat housing bypass, the coolant temp sensor sits in.

[junglejuice]

The 96 like all the pre-updates use two sensors for measuring temperature, the front one is for the ECU and can be easily tested with a multi meter set to OHMs and the rear one on the passenger side is for the guage only, also easily tested with a meter.
I would suggest getting hold of a digital infra red temperature probe and taking some measurements to see what temp the motor is, if done this way add around 5* for the coolant temp and you will be close.
To me it sounds like the viscous fan isn't working as well as it should but at speed it should run at or around "normal" temp if everything is working as it should....

[Browneee]

Ok well today I had errands to run around town. Temp started off not getting above 100' but after getting into traffic and stopping here and there temp sat above 95' and below 110' . Closer to the 110' when stop starting and 95' when being at speed limit for about 5 minutes. I've just got a gut feeling something is wrong ?.

Temp today was 36', another nice warm one ;-)

Just to clarify test the REAR sensor, if you ground it, the temp gauge should swing to full scale ? Which would mean the sensor is ok ?

Also just to clarify , if the thermostat is stuck closed the yep would sky rocket and never come down ? I know this one may sound like a stupid question but just want to make sure coolant does not by pass via another route if stuck closed.

One more.... If my fan clutch is worn out, when I start the car when she's cold I would hear a noticeable fan noise correct. On my old Nissan and Toyota both use to have a noticeable fan noise at start up until you either warmed the engine up or drove off quickly and the noise went away. Any one got any good SAFE tips to test fan clutch?.

[junglejuice]

The rear sensor is for the temperature guage, grounding it causing the guage to move only indicates that the guage is working, you need to know that the sender is reading the correct resistance for a given temperature, for that you need to know the "actual" temperature of the coolant and read the resistance and compare it to the table in the FSM, same for the front temp sensor.
As for the t/stat from memory the heater will allow some bypass but maybe the t/stat is only opening partially.
As for the viscous coupling you can test the amount of resistance it has against you trying to rotate it when both cold and hot, the FSM should have info on that as well but do it with the engine off, not running for obvious reasons....

[BLAKLISTED]

Hey mate, from what I've gathered to test the fan clutch start your jeep, let it warm up a bit. Then shut it off and try to spin the fan by hand. Should be quite hard to spin. If it spins fairly freely it may be on the way out. Heard of other tests jamming a rolled up news paper in the fan while running, and if it stops fan is buggered. Stuff that though!

[Browneee]

Hey mate, from what I've gathered to test the fan clutch start your jeep, let it warm up a bit. Then shut it off and try to spin the fan by hand. Should be quite hard to spin. If it spins fairly freely it may be on the way out. Heard of other tests jamming a rolled up news paper in the fan while running, and if it stops fan is buggered. Stuff that though!

Hahaha yeah read that once before in my old FJ40 service manual....

Well just went out side an ran car. Before I ran it there was some friction (not much) on fan clutch . Let the temp rise till THERMO fan came on a couple times then turned it off and tested fan. Before I cold test it the fan was spinning freely at engine idle rpm, so had to wait for it to stop before I could stick fingers in there to test friction. I thought it odd that it had to spin down after engine was shut off, as THERMO fan was coming on, so shouldn't the clutch fan engage ?.

[Browneee]

Oh an now I have a check engine light on!!!!!!!

[junglejuice]

Hahaha yeah read that once before in my old FJ40 service manual....

Well just went out side an ran car. Before I ran it there was some friction (not much) on fan clutch . Let the temp rise till THERMO fan came on a couple times then turned it off and tested fan. Before I cold test it the fan was spinning freely at engine idle rpm, so had to wait for it to stop before I could stick fingers in there to test friction. I thought it odd that it had to spin down after engine was shut off, as THERMO fan was coming on, so shouldn't the clutch fan engage ?.

Was it stiffer when hot?

[Browneee]

Was it stiffer when hot?

No where near..... So today I went and bought a new fan clutch, new top & bottom radiator hose more coolant and a heavy duty tranny cooler. I Installed everything and plumbed the cooler straight to the tranny by passing the original system . As soon as she fired up the roar of the fan could be heard even with revving the engine it could be heard. Haven't heard that sound in the 4 years I've owned her :-). Temp took ages to rise above 100', so with fingers crossed the problem has been solved. Hopefully with the new tranny cooler towing my wake boat should be a little kinder on the old girl. Now just for its 5k service and new tranny filter.

I will report :-)

[junglejuice]

Keep us informed....

[Browneee]

Took her for a long drive and temp never rose above 100' . Fan roar on acceleration was audible ( which I've never heard) .

I think I've had a win :-)

[Roler]

well deserved ;) A quick word on the viscous fan test. I tried to sort out that issue some time ago, spinning hot and cold, with resistance and spinning loosly, what should it feel like and when. despite multiple resources and expert opinions on this, it remains controversal. some say even spinning with resistance when cold, then slighlty better warming up, but when hot the viscous stuff again expands causing more drag. I dont know, I guess the truth is out there and since its not an incredibly expensive part ( overseas), replace it when in doubt. Enjoy the roar..

[junglejuice]

Here is an extract from the 95FSM...

TESTING
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.

HTH