Beat the Dead Horse. Overheating XJ

a_kelley

a_kelley

mechanical fixer
Joined
Jan 26, 2010
Location
Rutherfordton
Well, I've put a new pump, new t stat (with two 1/8" holes), new fan clutch, new cap style radiator, new coolant (been recycled 5 times already just on trying to get this fixed, tired of draining and filling).. looked clean inside block from the front side. I don't think its losing water. Running like 250 sitting idling, 217-225 down the road, 230 hard uphill.. had the heater valve out, put it in, thought maybe it flowing unrestricted let it bypass the thermostat.. a little better. I've got no way to check the sensor. unless I can like boil water and stick it in a styrofoam cup and drop the sensor in it, but by then it won't be boiling anymore. fan is not cycling, which would make it seem like the back of the head is getting hotter than the front? unless the coolant temp sender for the fan is bad.. i'd hate to have to put a head gasket in it.. it has a misfire every now and again, not sure if thats related. plugs all look clean with a hint of light orange..

the lower rad hose is significantly cooler than the upper rad hose, but then doesn't that mean its doing its job?

should I see flow in the radiator?

air trapped in the system?
 
Very possible u have a bubble in the system.jack the frontend up as high as u can,and with the radiator cap off crank it up and hold it around 3000rpm for a min. or two it will burp the system.u may have th doit a few time to gettem all out.best starting place and it dont cost anthing!:beer:
 
a_kelley said:
unlessss the coolant temp sender for the fan is bad..
Click to expand...
This. Ok, either this or the fan itself is bad. If you're running hot at idle, but not at cruising speed, the fan isn't coming on like it should. The airflow while cruising is keeping you "normalish". When you stop, the temp goes up and the fan should kick on. I'd try to hardwire the fan and see if it works first.
 
Is it the open or closed cooling system? Easy way to check the e fan is turn on the ac. Second easy way is to pull the relay and bypass the fan and make it come on. Chances are if its the old system or closed on e you have air in it.
 
my buddies XJ was running pretty hot for a while. we done away with the mechanical fan and wired up 2 electric fans on a switch and ran them all the time. worked for a while till he forgot to turn the switch on and blew apart the radiator. while the radiator was out we decided to go ahead and change the water pump since we were that close.
(like $30) turns out that was the problem all along, it didnt leak or squeak or anything but once i had it out i noticed some play in the pully where the bearings seemed to be bad. damndest thing! most pumps that go bad i seen showed some kinda sign. it runs a steady 170-180* driving.
now he only has to turn the fan on when in URE or while sitting still. could be your pump, could be your head gasket. sorry to ramble, just wanted to share what i had learned about the never ending XJ cooling problems.
i think the bubble in the system is a good place to start though.
 
ghost said:
Is it the open or closed cooling system? Easy way to check the e fan is turn on the ac. Second easy way is to pull the relay and bypass the fan and make it come on. Chances are if its the old system or closed on e you have air in it.
Click to expand...

New open style.. Fan does work, relays good.

willness33 said:
This. Ok, either this or the fan itself is bad. If you're running hot at idle, but not at cruising speed, the fan isn't coming on like it should. The airflow while cruising is keeping you "normalish". When you stop, the temp goes up and the fan should kick on. I'd try to hardwire the fan and see if it works first.
Click to expand...

Agreed it should kick on, of course that is assuming that the front of the head is not cooler than the back of the head... but I don't think thats all that likely.. either my temp sender is lying to my gauge+me or the temp sensor on the outlet neck for the fan is brokenp..
 
You have to have a power and ground for fan operation. Do you have either, or both?
The PCM drops the ground for the electric fan to operate. Turn on the AC, or wait for the temp to be very hot,this will force the fan on, see if you have continuity to ground at the fan connector. If not, the ground side is failed. Then check continuity from the PCM to the fan. If that is good, then you know the PCM is not providing ground for fan operation. You can always provide a ground if the PCM is not by simply running the ground side of the fan to a chassis ground.

Also, 4.0's tend to get air pockets easily. The way, bar none, to bleed a 4.0 is to unhook the heater hose at the thermostat housing while you are filling up the radiator. Thsi will push all of the trapped air up and out. I do this on every single 4.0 that I have ever touched with never an issue.

Also, do you know if the pump is actually pumping? I have seen impellors come loose on 4.0's. After bleeding, unhook a heater hose and see if coolant shoots out. If the pump is functional, it should propel the coolant very strongly.

Also, there are 2 different sending units (for the gauge, not the sensor for the coolant temp to the PCM). One for an idiot light, one for a guage. They are calibrated differently. Make sure you have the correct one.
 
Jody Treadway said:
You have to have a power and ground for fan operation. Do you have either, or both?
Click to expand...
both, I can remove the cover from the relay and push the contacts and the fan comes on.
Jody Treadway said:
The PCM drops the ground for the electric fan to operate. Turn on the AC, or wait for the temp to be very hot,this will force the fan on, see if you have continuity to ground at the fan connector. If not, the ground side is failed. Then check continuity from the PCM to the fan. If that is good, then you know the PCM is not providing ground for fan operation. You can always provide a ground if the PCM is not by simply running the ground side of the fan to a chassis ground.
Click to expand...
The fan will come on if I put on Max AC, but still runs hot.. and the AC is non-existent
Jody Treadway said:
Also, 4.0's tend to get air pockets easily. The way, bar none, to bleed a 4.0 is to unhook the heater hose at the thermostat housing while you are filling up the radiator. Thsi will push all of the trapped air up and out. I do this on every single 4.0 that I have ever touched with never an issue.
Click to expand...
I did it the opposite way, filled from the thermo sensor hole in the housing, til it came out the cap
Jody Treadway said:
Also, do you know if the pump is actually pumping? I have seen impellors come loose on 4.0's. After bleeding, unhook a heater hose and see if coolant shoots out. If the pump is functional, it should propel the coolant very strongly.
Click to expand...
The impellor was not loose on the new pump.. but I'll pull the hose and crank it and see..
Jody Treadway said:
Also, there are 2 different sending units (for the gauge, not the sensor for the coolant temp to the PCM). One for an idiot light, one for a guage. They are calibrated differently. Make sure you have the correct one.
Click to expand...
I got the sender for the gauge, The switch is black connector and the sender is a white connector. I don't think they really go bad often though? I drove the jeep this morning and it was fine, up til about 10am, then it started warming up, but it hasnt gone over 220ish.. I could kind of shake the upper hose and it sounded like sloshing inside, I'm thinking air in it?
 
Jody Treadway said:
Bleed it the way I suggested. It's the only way to effectively remove all air prior to starting the engine.
Click to expand...

Undid the heater hose off the thermo housing, coolant came out of the housing, the cap, and went down inside the hose.. no bubbles from the thermo housing. then cranked it and it spewed water at least 8" from the thermo housing from the heater hose... it shows codes for coolant temp sensor, fan relay ckt, and ac relay ckt. I'm going to check if the relays have power to them for the coil (believe so, I had just a wire hooking the fan relay to the ASD relay to run the fan when it was on only and it worked like that, kinda kludgey).. Which the AC clutch is not hooked up, nor is the freeze sensor in the heater box.. I had the CTS unhooked for a minute while it was on, that might have caused that to show, as well as having had the relay manually engaged, so i'm just all confused now. the fan did work before I swapped the motor, but it never came on unless the AC was running (of course that was the same harness in another vehicle that actually had the AC operational+hooked up) I'm about to go buy a infrared thermometer and see if it is actually as hot as advertised. does tygon/clear tube hold up to heat?

***
checked the power to the coil and the common side of the relay, both have power. reset computer, both the codes for the fan went away. ac clutch relay persisted, believe due to not having a low/high pressure switch.. recleaned all grounds underhood to raw metal-metal as well.

***
took the overflow hose, hooked a funnel to it, and hung it from the hood, absolutely higher than any line. took and flipped my lever cap open, ran the jeep til it got hot and revved it a few times, bubbles on let off, level drop, add more water, squeezed the hose a few times, bubbles, add more water, so on, so forth, and I can shake the upper hose now and not feel air in it.

***
Jody's method seemed to bleed best.. "The Holy Grail of XJ" (FSM) is no help, all it says if fill, cap, and fill overflow. posh. I'll just have to go borrow my buddy's pressure tester and see if the needle bounces with the combustion strokes or if it leaks somewhere or if I need to replace the sender and sensor.. After that the crow bar is looking good. Was wanting to go get a DD tomorrow with it but no way am I towing a car when its running 215-220 steady, sometimes up to the white line just before red and no fan action still. I can hold onto the upper main hose for a few seconds longer than the heater hose, no idea why. Infrared thermometer would be nice. Just how hot should the main inlet hose to the water pump get? I can hold it all day long (and there is a good spring in it, can't crush it under open atmosphere).. I suppose if the radiator is actually cooling, but I wouldn't expect it to cool that good, shouldn't it still get very warm/hot to the touch?
 
it is pretty common for the radiators in cherokees to get crudded up. i had that issue and since i could pick one up for cheap enough i just replaced it. i also installed a 1995 degree tstat and a aftermarket tranny cooler. my problem solved.
 
gt500swim said:
it is pretty common for the radiators in cherokees to get crudded up. i had that issue and since i could pick one up for cheap enough i just replaced it. i also installed a 1995 degree tstat and a aftermarket tranny cooler. my problem solved.
Click to expand...

bad brand new radiator out of the box? I Guess anything is Possible. I've never had trouble like this one's been giving me with new parts.. Going to re replace the thermostat, and the thermo sender for the gauge.. at least its under warranty
 
screwed with it some more.. holds pressure on the rad pressure tester when hot/running, no needle pulsing.. drained, checked rad, it dumps either way just fine.. pulled t-stat, refilled Jody's way, revved to 2-3k rpm and got some air out of it, then left it revving and it began fizzling/foaming/miniature bubbles at the radiator neck.. and still running 215, an no electric fan action... misfires at hot idle, but not cold idle. head gasket? any place I can buy (off the shelf) exhaust gas dye to drop in the coolant?
 
grr 3rd rewrite nc4x4 kept rejecting it, said page invalid or session expired.. gr.

anyways. pulled head off, clean gasket surfaces, inspected head, inspected gasket, nothing.

Unless you can spot something.

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Ok for the panoramics, I did them by hand in GIMP, and I'm not patient enough to fudgle around with aspect and lens curvature and I don't feel like finding a good panoramic image merger for Linux/X-win.

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I put it back together, torqued to spec.. installed a Brand New Verified in Boiling Water tstat and gasket.. Filled using Jody's remove upper heater hose, Did that. Attempted to purge upper hose by squeezing, got some air out of it.. well cranked it up, let it warm up and t-stat opened, took some more, let it run a bit, and it just spewed up out of the neck when it got hot enough. I don't know exactly, maybe 220 - 230 degrees.. nor do I know the Antifreeze concentration since I've reused it and added water like 20 times now. well under 33%.. Could it be a bubble trapped back in the head by the sensor? The motor was a 97 but I drilled and tapped the sender for the gauge in the same location as on the old motor.. seems to not hit anything internally, so I dont think the sender is touching like say the water jacket side of the exhaust port..
 
overflow hose diameter is not critical is it? I got a hose that i had to use a screw driver to flare the end before I could put it on the tank or radiator.. so probably 1/8 or 3/16 hose.. wondering if making the hose smaller than intended changes to amount of vacuum it has to pull to draw back water into the system...
 
grabbed an IR thermometer.. +/- 2.5% error, so at 220 degrees error is 5.5 degrees either way. So the thermo outlet never got over 220. However, the back of the head, away from the exhaust hits 200, and measured on the front, the same, but when I edge to 1/8" off the manifold, the temp goes up to what I'm seeing on the gauge. Inside the head, underneath the sensor by 1/8 or 3/16 is... an exhaust passage. Wonder if thats why they did away with the coolant temp sender and went to using just one on OBD II, also would eliminate another sensor to go bad. That also explains why the cooling fan is not kicking on...

I came up with a solution.. drill and tap the thermostat housing on the flat boss by the long bolt, and relocate the coolant temp sender in there... and plug the port I made in the back of the head... of course there is always the what if of if the sender is actually reading coolant temp, and not just the locally disturbed temperature from the exhaust port. The other motor read the same way (and it was a 93), however, I mean it could still be the sensor, but I'd need to pull the valve cover to change it, since I can't get it to turn, cause the valve cover keeps a box end off it, or a socket, and the open end just flares+slips off. Also could just be a flawed design and thats why they changed it.
 
with our first real "hot" day yesterday (3/19) my wrangler was holding around 220 going down the interstate. i was actually thinking about it the other day driving and when my catalytic converter finally clogged up my motor was misfiring and hesitating like crazy. even with a 180 degree thermostat and in the city my temps were reaching 220 easily. try removing the exhaust from the manifold and run it to temperature or drive it down the road and see what happens. when i did i found a whole lot of power i never knew i had and the temperature dropped dramatically to 190 at WOT
 
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