Need help troubleshooting overheating 258 in XJ

rockcity

rockcity

everyday is a chance to get better
Joined
Apr 10, 2005
Location
Greenville, NC
Need help troubleshooting overheating 4.0 (not 258) in XJ

The darn XJ started to over heat yesterday afternoon. About 2 months ago, I replaced the water pump and a couple other misc. engine parts. The old pump was leaking around the seal and I just decided to replace it once I had it off. Anyway, its been fine ever since yesterday. I checked my fluid, not lower than normal, so I added some to be sure. No change. Checked oil and its still good (not burned up or low) and the same for the AT fluid. Was about a quart low, no biggie, added to top it off, but still no change (thought maybe the hot fluid in the radiator may keep the water hot????) I'm no mechanic, just a fabricator, so I tried everything. The thermostat was new about a year ago, so I didn't change it with the water pump.

It doesn't drive any different, sound any different than before, but now its just overheating and seems as if its getting worse.


Any ideas??? I'm taking it into the shop Monday, but if its something simple we can figure out, maybe it'll save me a few $$$.

HELP!

Rob
 
heck yeah that thing is freakin hot. I just felt the cap and could only put my hand on it for like 2 seconds. Same thing with the radiator.
 
Don't XJ's have an electric fan on them as well as a mechanical? If so, I'd check that.

Also, I'd look real close at the level of the ATF.. Hopefully the barrier between coolant and ATF hasn't sprung a leak.. (I would think the higher pressure of the ATF would force it into the rad)

Or, hell, it could just mean that you should get your radiator cleaned!

My $.03 (adjusted for inflation) :D

P.S. - The title of this thread is what they ALL should be - descriptive of the question.. :beer:
 
oops, its a 95 4.0, not a 4.2. I'm so used to haveing a 258 in my CJ, I just unknowingly typed. good catch.

fans seem to be working fine. radiator has been cleaned and has all new coolant in it. The AT is just leaking a little, but its not leaking into the radiator, from what I can see by looking at the coolant.

To start, I'll prob. replace the thermostat (remove and check for inconsistency first) and then change the oil, its due soon anyway, then, well, I'm running out of stuff to try.
 
What kinda temps are you getting up to?

Let it cool off,pinch off bypass hose, remove the cap, crank it up, see if the coolant is moving by looking in the rad cap hole? does it move after warmed up?

trying to see if T-stat is working properly and if the pump is moving the coolant.
 
Also check for collapsed radiator hose also I would verify with thermometer to be sure its not just a gauge/sending unit prolem.

My .01 worth
hell Rich and all the inflationists stole my other .01
 
I swaped out the 195 thermostat for a 180. I'll find out tomorrow if it works when I drive it 15 miles to work. The other thermostat looked good, but I don't think I'd know what a bad one looks like. I can do the work, I just can't tell ya whats wrong with this crap.

We'll see what happens tomorrow.


Rob
 
Cant tell bad thermo by looking, easiest way is to put in pot of water on stove with meat thermo, you will hear it open and just look at the thermo..
 
I had an overheating and had a "good" flush job done and the problem is gone.
 
well, I drove this morning (5am) and it was ok. didn't get over 205, but it wasn't blistering hot outside either like yesterday. It didn't "overheat" but I still don't think its quite right.
 
Just for giggles...you sure the gauge is reading right?
 
I may have mentioned this in an earlier post, not sure, but a quick way to check both the gauge and sender... you can get a diagnostic thermometer at most ADvanced or autozone NAPA wherever or a cheap meat thermometer then remove radiator cap ( whiwe cool of course :flipoff2: ) crank and let get up to normal op temps you can stick the thermo into the radiator neck and get an acurate reading on coolant temp at radiator. If it matches the gauge, the you know both sending and gauge are acurate and can start looking elsewhere.
 
not a bad idea. I may try it before I take it in to the shop, which will not happen just yet as I try and figure out this bug.
 
well, I've spent that last couple of hours working on the XJ.

Found no real solution. Came home from work toay around 1:30 and it was running up around 230 or so running at 60 mph. Thats with a new 180 thermostat. All hoses are running about 190-200F when I checked with a kitchen thermometer and the engine running at about 230, according to the gauge.

Turned AC on and there was no real change. Turned heat on and no noticable change. At idle, its ok, its just when it revvs up around 2K rpm that I notice it the most. More rpms = faster increase in engine temp.

Next thing to check? Maybe replace the rad. cap and the temp. sending unit (cheapest couple things) and then go from there???



Rob
 
If all is well with cooling system, revving engine should increase fan draw and if anything cool engine slightly, thus why most boilovers occur immediately after shutting engine off.
If thermometer is giving you a coolant temp of 180-190 I would start checking gauge and sending unit.
Good news/Bad news here sending unti cheap and easy, gauge (most likely not 100% on XJ) is part of PCB dash and would probably be best fixed with aftermarket gauge.
Wish you were closer to CHT, I ve got plenty of test equip to sim voltage and check the gauge
 
I'm not sure if these have electric and mechanical fans but are either working? You said the thermostat has been changed, radiator has been flushed only other options I would know of is to get a new rad cap check the sending unit or go to the rear and smell the fumes coming out. I think you could tell if there was a blown head gasket though. Could possibly be the timing? How many miles does the engine have? The last thing I could think of would be to flush the block. It would have to be a high milage engine for that though, unless someone put that block sealer crap in it.
 
well, its got normal mileage, about 140K miles (I guess high mileage), but never given us any major problems in the 6 years we've owned it, until now. I have replaced the water pump before this last time I did it, but they are cheap and if I had to pull it off to fix the gasket leaking, I put a new one in there just to be sure I didn't have to do it as soon in the future. Changing that thing in an XJ is a pain!!!

The rad. hasn't been flushed, but IIRC, it was replaced a few years ago. The timing doesn't seem to be off, but I know if it is, it will make it overheat. That'll be something I check next as well cause its free. Not a blown head gasket, I've had one of those and that sucks!!!!

I could flush the block and whole cooling system. The coolant looks brand new, exact same as when I put it in there, but I don't think that really matters too much.

Right now I'm gonna go check the temp of the fluid. Now that its cool enough to open the cap, it'll be much safer :)

I'm getting hose temps in upwards of 200F, I hope thats about as hot as the fluid, but I doubt it.

Rob
 
ok, coolant temp. maxed out the 220F kitchen thermometer, so I know coolant in the radiator is getting to at least 220 and then some, cuase it rose very quickly, from 140 up once I revved the engine (between 2and 3K rpms for a period of about 30 seconds. Once I let off to idle, the coolant spewed out the fill cap like when it overheats. Now I know I gotta put more fluid in.

Maybe I don't have enough fluid in there? I know someone somewhere said something about getting the air out of the system, but I think it was for an open system?? how do I tell what system I have?

Rob------------> off to the parts store for a cap and sending unit.
 
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