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Overheating issue

Old 02-11-2019, 12:17 AM
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Default Overheating issue

Hey there just bought a 92 Xj , it has the inline 6 4l with auto and 4wd. I replaced oil ,filter , thermostat, air filter , valve cover gasket as precautionary. I drove it for a good 30 minutes home before all that . But now when I turn Jeep on within 5mins the gauge says itís overheating, Iíve got it close to redline and coolant hoses all felt cold so I risked opening cap n coolant wasnít even warm. So with my trusty harbor freight ir thermometer (just kidding idk how accurate it is) I checked some spots.
Driver side of Head 400f

exhaust 800f

Front sensor 190-210f

Rear sensor 230-240f


Another note - Iíve mostly owned fords so Iím in uncharted areas with this Jeep but top of valve cover is quite warm - my Bronco II can drive for hours without the cover heating up

also when bleeding the coolant system - I refilled -squeezed hoses - topped off and the started car with cap off - coolant almost immediately begins to overflow ďfiller neckĒ - first time in bubbled a bit getting air out of system but second time it just started spilling out without bubbles
once again with bronco it usually takes a few mins before this happens




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Old 02-11-2019, 12:30 AM
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Operating temp is 210 on these.

I'd bet the temp sending unit (driver's side, back of head) is bad and pegging the gauge. Probably when you go to remove the plastic wil crumble apart.

Unless the gauge is reading 230-240, in which case you probably have blocked coolant passages or a disintegrating water pump impeller.

If you have no idea how old the water pump is- replace it and flush the system really well with a garden hose when reinstalling it.
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Old 02-11-2019, 12:33 AM
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Did the coolant get sucked down before the overflowing? Usually the overflowing you describe comes after the 2nd top-off the few times I've done it.
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Old 02-11-2019, 12:38 AM
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Engine compartment is really hot on these - valve cover being warm is quite normal. I drove for 20 minutes today before doing my valve cover gasket and it was still warm to the touch 15-20 minutes after shutting the engine off (in 30-ish degree New England Febtober).
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Old 02-11-2019, 12:47 AM
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Iím assuming pretty old , oil was thick n nasty - will probably end up changing again in a week - but I donít think this car has had the tlc it deserves- is there any way to check either ? Weep hole leaking ? Multimeter On sensor?
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Old 02-11-2019, 12:57 AM
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And yea first time i bled it bubbles n dropped, then started overflowing and bubble at same time - 2nd time around there was no bubbling just spills out , and after like a min the exhaust doesnít smoke , so Iím hopeful itís not a head gasket
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Old 02-11-2019, 12:58 AM
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For the sending unit you've already done the usual test - does the temp on the tstat housing or back of head match the gauge. It's a single wire connector, if that wire grounds out it will peg the gauge.

The water pump can do the weep hole leak to indicate the bearing/seal is worn, but there is a somewhat common issue that there's no good way to know without removing the pump - the impeller will rust/disintegrate over time and hence not move the coolant very well.

The pump is easy and inexpensive to replace, it's so important that if you have any question, I'm of the opinion you should replace it just to be sure.
This comes from a man who has found himself changing a water pump on a Jeep I6 on the side of a highway 1000 miles from home. The plastic impeller snapped clean off inside the fairly recent Autozone special pump.
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Old 02-11-2019, 01:02 AM
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Bleeding behavior sounds normal. These engines are really tough - head gasket failures are far less common on these than other engines (aside from the 0331 defect - but on an older XJ that's not a worry).
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Old 02-11-2019, 01:17 AM
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Okay cool back of Block sensor matches gauge , which Iím assuming is one for the gauge since it only has 1 wire - although I will replace since I donít like questioning coolant parts - and thank you for confirming thatís normal - always nervous when I encounter a new car wondering if everythingís normal - I figured valve cover due to engine layout and although I will replace water pump due to your suggestion and the amount of rust in coolant ports,I assume the propeller was probably held together by all the gunk and draining was the last straw - just wanna understand it better tho , why would pump be acting up if itís still able to move fluid out the filler neck?
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Old 02-11-2019, 10:14 AM
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Yes, the sensor at the back of the head is the coolant sensor. It is strictly tied to the gauge. The sensor in the t-stat housing is the CTS that provides info to the Computer.

Since the gauge matches the back of the head, I can only assume that coolant is not moving sufficiently through the engine to cool it down. It's close, the t-stat temp seems to be right on point, but the temp is inconsistent across the engine.

This means, again I'm assuming, that either there are blocked coolant passages in the engine OR that the pump isn't moving the coolant. I would not immediately assume a bad head gasket or issue with the block or head since these problems are rare UNLESS you have obvious symptoms of such a problem (milkshake oil, white exhaust, coolant loss, etc).

The pump COULD be acting up because it's very old and it is common on this engine for the pump impeller to rust away and provide -some- but not -proper- coolant flow.

I recommend replacing the water pump because it will allow you to:
1 - Know for sure that the pump and impeller are in good condition and will move coolant correclty
2 - Take a hose to the opening while the pump is out and give it a really good flushing.

Once you've got the old pump off, you'll know right away if the issue is more pump-related or if it's more passages-related. If the pump is obviously in bad shape, then I'd flush and re-install and see where it's at. If the pump is in reasonably good shape, then I'd do as much flushing as possible and then probably run some flush chemical through it.

As I mentioned, I got stuck on the side of the road 1000 miles from home (the full story is much worse than just the pump on the side of the road...) due to a failed water pump. Being that a new quality pump is only $30-ish and it's a simple enough job to successfully complete with your "carry" tools on the side of the road 1000 miles from home - nowadays if I even -start- to question whether I need to replace the water pump - I'm replacing the water pump.


Edit ------ In short - It's common for this engine to have a water pump rust away over years of service such that it provides -- some -- flow in the system, but not enough to maintain the correct temp.

Last edited by PatHenry; 02-11-2019 at 10:19 AM.
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Old 02-11-2019, 02:14 PM
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Okay cool weíll i got the water pump and sensor but before I put them in I did a couple more tests. I threw one of those pressure relief radiator caps on , kept it open while watching resovoir - it filled up about halfway and then presumes to bubble inconsistently - ie big bubble - bunch of small bubbles then stops for a few seconds - but not in the same sequence or consistently- whatís ur thoughts on that? Just wanna ensure i find / fix problem rather than band-aid and have it reappear
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Old 02-11-2019, 02:36 PM
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Originally Posted by Griffin Healy View Post
Okay cool weíll i got the water pump and sensor but before I put them in I did a couple more tests. I threw one of those pressure relief radiator caps on , kept it open while watching resovoir - it filled up about halfway and then presumes to bubble inconsistently - ie big bubble - bunch of small bubbles then stops for a few seconds - but not in the same sequence or consistently- whatís ur thoughts on that? Just wanna ensure i find / fix problem rather than band-aid and have it reappear
Hmmm. Not sure - I've never tried that before.
The system does self-bleed the air out over time, so one can hope that it's just that.

What I'd do is get the water pump on and see if there's a smoking gun. If a thorough flushing and new pump do not correct the issue, you may have a tiny head gasket leak that's getting exhaust gas into the coolant but maybe so small it's not giving any white smoke or coolant smell out of the exhaust. At that point (or earlier if you want to be sure) maybe pick up a coolant test kit to ensure there's no exhaust gasses in the coolant.
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Old 02-11-2019, 04:09 PM
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So odly enough I picked up one of those test kits, tested fine - I noticed the bubbles stop slightly after and engine temp dropped and then raised back to about 220 and stayed there - hoses all got warm and worked well - Iím now sure that something is clogging the water passages and prevent fluids from filling the whole system and letting me purge air properly , time to change water pump and flush system to see what comes out - where is the drain plugs for these - donít wanna pull hose again
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Old 02-11-2019, 04:13 PM
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And thank you pat for helping me out, I really appreciate it - coolant problems always scare me especially when itís my wife driving car sheís not as quick to catch problems before they escalate
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Old 02-11-2019, 04:40 PM
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There's a drain on the radiator (I wouldn't bother with this - I worry I'm just going to snap it off). You're going to have to remove the lower hose anyway to change the pump, so that's how I'd do it.

Anytime bro - much of what I throw out there is stuff I learned by spending too many hours at work on this forum. The cooling system I do have a fair amount of personal experience on. Too many Autozone parts and youthful naivete on my old wrangler.. However, the coolant systems on these Jeeps are super easy aside from the Heater core and parts are easy to find and inexpensive. Once you get the crap cleared out of there and everything's working correctly, just tell your wife to check the temp gauge every once in a while and if it's past the middle/more than "half a tank", to let you know.

These engines are absurdly tough -- my Dad drove his 94 XJ over 400k miles, no major part replacements, never a problem, engine ran perfectly when he retired it. I feel it would've gone to 500k+. I put over 300k on a 00 TJ (which has a casting defect in the head where it cracks - the 0331 head failure) it never cracked on me, I had 1 "engine issue" (a broken valve spring) the entire 300k and as far as I know that engine runs great to this day. Rust ended DD-ing of my Dad's XJ and a blown NV3550 tranny (plus lots of minor issues and the fact gas was $4/gal at the time) ended DD-ing of my TJ.
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