Running too cold

[OkieXJ]

Isn't the temp sender a one wire connection? I think mine in on the driver side of head at the back of the engine by the windshield, and it was my understand that it only operated the guage/idiot light. I though the one in the thermostat housing was used by the engine computer.

Thanks for the empathy! I think I could almost fit the fan and clutch in my lathe, but it might be too small.

 

[87manche]

91-96 do. Temp senders on XJs:
* on the driver side of the block under the manifolds (RENIX, think this one is for the ECU?) yes, needs to see 160-170 to go closed loop
* on the back driver side of the head (RENIX and 91-96) - for the gauge cluster
* somewhere on one of the hoses (RENIX, for the e-fan?) In the radiator actually, drivers side in the tank.
* on the tstat housing (91-01. 91-96 it is only for the ECU, 97-up they eliminated the separate gauge sender and the ECU feeds its temp sender signal to the IP via the CCD bus.)

I know that I used the HO water outlet on the renix and just plugged it with a brass fitting. It might be handy later. I had to replace it anyway since mine came apart in my hand upon removal.

If I ever put an automatic E-fan in I'll use the thermo housing for the sender since I've converted to HO cooling and have no sesnder in the radiator.

 

[joe_peters]

ZJ HD fan clutch spins at 30 percent of shaft speed when not engaged and at 80-90 percent of shaft speed when engaged.

Standard fan clutch is 30 percent of shaft speed when not engaged and 60-70 percent of shaft speed when engaged.

The best test of a fan clutch is temperature reduction in the cooling system:

From the 90 FSM:

"The cooling system must be in good condition prior to performing the test outlined below to ensure against excessively high coolant temperature.

CAUTION: Ensure that there is adequate fan blade clearance before drilling.
(1) Drill a 3.18 mm (1/8 in) diameter hole in the top center of the fan shroud.
(2) Insert a dial thermometer -18 degree to 105 degree C (0 degree to 220 degree F) with an 8 inch stem, or equivalent, through the hole in the shroud. Ensure that there is adequate clearance from the fan blades.
(3) Connect a tachometer and an engine ignition timing light (to be used as a strobe light).
(4) Block the air flow through the radiator by securing a sheet of plastic in front of the radiator (or air conditioning condenser). Use tape a the top to secure the plastic and ensure that the air flow is blocked.
(5) Ensure that the air conditioner, if equipped, is turned off.
WARNING: USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS, OR FAN. DO NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm with the timing light (strobe light) aimed at the fan blades. Within ten minutes the air temperature (indicated on the dial thermometer) should be 88 degrees C (190 degrees F). Satisfactory operation of the fan drive requires that it engage before or at 88 degree C (190 degree F). Engagement is distinguishable by a definite increase in the flow noise. The timing light will also indicate an increase in the speed of the fan.
(7) When the air temperature reaches 88 degrees C (190 degrees F) remove the plastic sheet. Satisfactory operation of the viscous fan requires the air temperature to drop 20 degrees F (11 degrees C) or more. A definite decrease of audible fan air flow noise should be noticed. Replace defective fan assemblies."

 

[OkieXJ]

I gathered some more data as soon as I got home. My temp gauge was a little above the second strike which I guess was around 165-170. I got my thermometer which is a cheapie from autozone but still seems to work pretty well. The thermostat housing is measured 195, the upper radiator hose measured 145 and the hose that goes from the thermostat housing to the heater valve measured 170. Seems pretty weird. Is 195 the normal temp for a thermostat housing or should it be 210?

 

[kastein]

Probably depends on flow rate and insulation on the hose. A heater hose always has coolant flowing through it and is smaller, thinner, and right next to the engine, so it'll stay warmer than the thick radiator hose that has its flow limited by the thermostat. Thermostat housing is metal, and I would expect to see it right at the thermostat temp, while the coolant that's still inside the engine would be a bit higher (210 in this case.)

 

[OkieXJ]

If the normal temperature for the thermostat housing is 195, then perhaps my gauge is not working correctly and the Jeep is running the proper temperature and my mileage is low due to something else. Coolant comes out of the thermostat to the radiator to be cooled off correct? I'll have to do a more comprehensive test on my temp sender or replace it.

 

[Jeff in VA]

subscribing to this thread.....

I've got the exact same problem going on with the MJ. Spent half of Saturday installing the *third* new t-stat (Stant superstat 195 deg) with marginal success. Before this new one, it wouldn't even get to the first hash mark on the gauge, now it's at or just a hair above when driving. If I let it sit and idle it gets up around 180, but as soon as I start to move it dives back down.

I've got an infared thermo gun I'm gonna shoot temps tonight.

The only thing I can think of, and this is a longshot, is that I rebuilt the 4.0 before I dropped it in. I pulled all of the welch plugs and found a good amount of crud (chunks, actually) built up between the cylinder sleeves....and I spent a good amount of time with scrapers/screwdrivers and a shopvac cleaning out the block before installing the new plugs. Maybe I shoulda left all teh junk in there....:gag:

Jeff

 

[bdahlg]

Subscribing also. On my '91 I've replaced numerous thermostats, fanclutch, radiators, cap, heater core, flushed/drained an uncountable number of times: still the same freakin' thing. Blocking off half the radiator helps, but as soon as I start pushuing the accelerator, it shoots down as Jeff in VA describes. Takes a little more than a half hour to "fully" warm up and then teh temperature swings at a minimum.

Maybe our cooling systems are just workimg TOO effectively???

 

[OkieXJ]

I've got the exact same problem going on with the MJ.

I was hoping I would see this with it followed by and this is how I fixed it!

Maybe our cooling systems are just workimg TOO effectively???

Ha! Thats the way is seems. Overheating before, now overcooling :doh:. Hopefully we'll figure it out. I didn't have time to block off my radiator yesterday but I'll do it today and post up my results. I've been toying with the idea of building my own thermostat controlled by a microchip but that would be pretty time intense. Hopefully it can be solved some other way first.

 

[87manche]

If the housing is at 195 the thermostat is working properly, or at least close enough.

Somewhere around here (yeah I know, vagueness FTW) there is a chart of the temp sender ranges and what the resistance at a given temperature should be. I think you need to pull your temp sender and verify that it's within spec, if not replace, if it is then I would clean up all the wires. The temp sender is a single wire resistor basically, so any added resistance in the circuit makes it not operate properly.

Here's the chart, I think:
http://www.explorerforum.com/photopost/showphoto.php?photo=30138&size=big&ppuser=42004

The renix temp sender is just a GM part, so this chart is accurate for me, I'm not sure about the HO. You can see that resistance goes down as the sender warms, so added resistance in the circuit would make your gauge read cold.

While you're at it I would check over the one in the side of the block as well, because that's the one that the ECU reads and tells it that the motor is warm and ready to go closed loop. The one that drives the gauge is just to make you feel good.

 

[OkieXJ]

Thanks for the tip! I'll check it out. I think the sensor the ECU reads on a 91 is in the thermostat housing. I'll try to do some research on how to check it out.
BTW: the chart in my 93 FSM for the Coolant Temp Sensor is different than the one from that link. They changed sensors between the years I suppose.

 

[87manche]

Yeah I just went and looked at Kens info, it would be the thermo housing for you.


I R HO illiterate.

 

[bdahlg]

...I think the sensor the ECU reads on a 91 is in the thermostat housing...

Yes it does. The one on the driver's side at the back of the head next to the valve cover is the one that reads for the temp gauge on the cluster.

 

[kastein]

My MJ will actually heat up in less than a mile of city driving - figure about 5 minutes. I can hop in and head for work and by the time I get on the highway it is at 190 or higher... unless it's winter, then it runs at about 180 at highway speeds.

The 96 takes quite a while to heat up and has been running at the first mark (the one at about 11 oclock) so I think that the thermostat is stuck open. That plus the massive holes in the downpipe (ripped LCA and UCA mount off when I did an endo while wheeling, the pinion yoke chewed holes into it even with the stock dent) are probably what is wrecking my gas mileage right now. If I have any spare time in the next week or so I'm planning on fixing this.

 

[OkieXJ]

I couldn't find any information on how to check the temp sender that works the gauge for proper function in the FSM. They have one on Rock Auto for $10 I might pick up though.

 

[joe_peters]

Drop the sender in a pot of water with an ohm meter attached and a thermometer. Heat the water.

Application & Test Temperature Ohms
100 F (38 C) ...................................... 1365.0
220 F (104 C) ........................................ 93.5
260 F (127 C) ........................................ 55.1

If you want to test the gauge purchase a number of resistors at Radio Shack to equal the above values and use them on the sender wire.

 

[87manche]

Drop the sender in a pot of water with an ohm meter attached and a thermometer. Heat the water.

Application & Test Temperature Ohms
100 F (38 C) ...................................... 1365.0
220 F (104 C) ........................................ 93.5
260 F (127 C) ........................................ 55.1

If you want to test the gauge purchase a number of resistors at Radio Shack to equal the above values and use them on the sender wire.

This, use alligator clips. Ground clipped to the threaded part, hot clipped to the post where the wire attaches. Watch fr resistance at a given temp. Some variation is OK, call it 10%.

Joe's numbers are probably correct for the HO sender.

I'm real good on vague and generalizations

 

[OkieXJ]

Blocked off half the radiator for the drive home, made no difference. I'm leaning toward a bad temp sender and gauge problem so I'll be testing that soon. Its cooooold out now though so it probably won't be tonight.

 

[Glenn B]

Ouch, 5 t-stats to get one that works? That would piss me off to no end.
Autozone t-stats are made in Israel (surprisingly not China)... have never seen one come back.
I have looked at the AZ Valu-craft, the Duralast, and the FailSafe... no noticeable/visual difference. But I went with the failsafe, as I know when the temps are back to 100+ this summer, I will likely get too hot again.

So far so good, went from running too cold in the winter to holding right at 205-210.

Just unscrew the phillips screws holding the grill slats in, insert cardboard between header and radiator, replace grill. Takes like 10 minutes. I did it on my 87 because it took like 5 thermostats to get one that worked.

even after I did my closed/open cooling conversion/water pump, thermostat housing I kept that t-stat.

I blocked off 50% of the radiator on the passive side of mine (no elec fan for me) so that the mech fan would cool it if I idled for a long time.

 

[Jeff in VA]

mebbe I oughta just try an el-cheapo and see if it makes a difference......

FWIW, the old Stant I took out I could push open with my fingers with noticeably less force than the new one I put in, but I couldn't move either one more than 1/4" or so.

I can't believe that little of an opening could make such a difference, but I ain't no engineer or nuthin'......

Jeff