Potentially overheating 4.0, stumped and need help!
Thread Starter
CF Veteran
Joined: Apr 2011
Posts: 1,146
Likes: 0
From: Clayton, NC
Year: 1988
Model: Cherokee
Engine: 4.6L I6 Stroker with port matched +99 intake and 62mm TB
Potentially overheating 4.0, stumped and need help!
***ISSUE RESOLVED!!!***
First off, this may be a bit of a long post, but please bare with me as I try to explain all that's been done thus far in an attempt to rectify this issue...
About a month ago, I picked up another cheap-Jeep. '95 XJ Sport for $300 in need of some strong TLC. PO sold it because it was overheating, and suspected the head gasket. He had owned it/been driving it for just shy of three years, which was verified after looking over the title. First thing I did was check the oil, the radiator (which was empty except for a thick layer of rusty paste), and I peered down into the valve cover through the oil cap. Just a very basic diagnosis. I agreed to buy it, and my buddy and I dragged it home.
I started by filling up the coolant system with water. Started it and let it idle, and it went into the red-zone, so I shut it off. I noticed it was steaming from the back of the head. Okay, PO was right ...so I thought. I removed the head, inspected the gasket (which had been replaced before at some point, not by the PO, so he claimed), and the gasket didn't show any signs of breakage or cause for concern. I next cleaned up the head which was dirty, both inside and out. Found a small pin hole in the freeze plug that I concluded was the cause of the leak. No problem, I thought. Flushed the head with a garden hose and some strong cleaning chemicals, popped a new freeze plug in and painted it for my own pleasure. While I had the head off, I replaced all the valve stem seals and cleaned up all six intake valves as they were covered in a thick layer of carbon and burnt on oil. Also, while the head was off, I removed the freeze plugs in the side of the block, flushed each coolant galley/port, and flushed through the side of the block, before replacing those five freeze plugs with new ones.
New M.L.S. Mahle/Victor Reinz head gasket, sprayed with Permatex Hi-temp Copper gasket spray, new head bolts, torqued down using the 3-step sequence specified by my Haynes repair manual, and I reassembled the manifolds, etc. In addition to those new parts/gaskets, I've installed a new "high-flow" 195°F thermostat, water pump, new radiator (because the old one was assumed clogged or partially clogged from rust-paste), and new temperature sensor for the gauge (since I broke the original one removing the head... D'oh!). Currently, I have the coolant system filled with Prestone coolant system flush and distilled water. This is actually the second time it's been filled with that because the first time I filled it, I ran in and drained it to do an initial flush. It was quite dirty to say the least. Upon looking at the water/flush mixture, I see no signs of engine oil. It's just brown from what I assume is more rust that I couldn't get out via my garden hose flush.
Anyway, as it stands, it still overheats (or at least the gauge indicates it does). I have started it and let it idle for 20-30 minutes at a time once engine temp stabilizes, about 4-5 times now. In each case, NOTHING leaks, no boiling over or steam, no white smoke from the tailpipe, no erratic running, misfire, or engine stumbling. It idles perfect, revs fine, and shows no signs of ill fortune. I even rented a coolant system pressure tester from AutoZone, pumped it up to 17-18 psi and left if pressurized over night, and the next morning it may have lost a half to one psi. In addition, the electric fan is never triggered to come on, but if you turn the A/C on, it comes on like it's supposed to. Also, out of curiosity to see if the factory temperature gauge is off, I swapped in another instrument cluster and the same thing happens. I'd like to note, that in each time I've had it running for those 20 minutes or so, the factory gauge needle rests as the bottom end of the red-zone. Oil pressure, if it matters in this case is damn near perfect at 40 psi at idle.
One thing I want to do is to check the engine, head, and coolant hoses with an infrared 'point-&-shoot' style temperature gauge to see what it's truly running at, but I don't have access to one at the moment.
So, what, if anything, am I missing? Any suggestions or thoughts? I know my way pretty well around these 4.0s, but this has me stumped and highly frustrated.
First off, this may be a bit of a long post, but please bare with me as I try to explain all that's been done thus far in an attempt to rectify this issue...
About a month ago, I picked up another cheap-Jeep. '95 XJ Sport for $300 in need of some strong TLC. PO sold it because it was overheating, and suspected the head gasket. He had owned it/been driving it for just shy of three years, which was verified after looking over the title. First thing I did was check the oil, the radiator (which was empty except for a thick layer of rusty paste), and I peered down into the valve cover through the oil cap. Just a very basic diagnosis. I agreed to buy it, and my buddy and I dragged it home.
I started by filling up the coolant system with water. Started it and let it idle, and it went into the red-zone, so I shut it off. I noticed it was steaming from the back of the head. Okay, PO was right ...so I thought. I removed the head, inspected the gasket (which had been replaced before at some point, not by the PO, so he claimed), and the gasket didn't show any signs of breakage or cause for concern. I next cleaned up the head which was dirty, both inside and out. Found a small pin hole in the freeze plug that I concluded was the cause of the leak. No problem, I thought. Flushed the head with a garden hose and some strong cleaning chemicals, popped a new freeze plug in and painted it for my own pleasure. While I had the head off, I replaced all the valve stem seals and cleaned up all six intake valves as they were covered in a thick layer of carbon and burnt on oil. Also, while the head was off, I removed the freeze plugs in the side of the block, flushed each coolant galley/port, and flushed through the side of the block, before replacing those five freeze plugs with new ones.
New M.L.S. Mahle/Victor Reinz head gasket, sprayed with Permatex Hi-temp Copper gasket spray, new head bolts, torqued down using the 3-step sequence specified by my Haynes repair manual, and I reassembled the manifolds, etc. In addition to those new parts/gaskets, I've installed a new "high-flow" 195°F thermostat, water pump, new radiator (because the old one was assumed clogged or partially clogged from rust-paste), and new temperature sensor for the gauge (since I broke the original one removing the head... D'oh!). Currently, I have the coolant system filled with Prestone coolant system flush and distilled water. This is actually the second time it's been filled with that because the first time I filled it, I ran in and drained it to do an initial flush. It was quite dirty to say the least. Upon looking at the water/flush mixture, I see no signs of engine oil. It's just brown from what I assume is more rust that I couldn't get out via my garden hose flush.
Anyway, as it stands, it still overheats (or at least the gauge indicates it does). I have started it and let it idle for 20-30 minutes at a time once engine temp stabilizes, about 4-5 times now. In each case, NOTHING leaks, no boiling over or steam, no white smoke from the tailpipe, no erratic running, misfire, or engine stumbling. It idles perfect, revs fine, and shows no signs of ill fortune. I even rented a coolant system pressure tester from AutoZone, pumped it up to 17-18 psi and left if pressurized over night, and the next morning it may have lost a half to one psi. In addition, the electric fan is never triggered to come on, but if you turn the A/C on, it comes on like it's supposed to. Also, out of curiosity to see if the factory temperature gauge is off, I swapped in another instrument cluster and the same thing happens. I'd like to note, that in each time I've had it running for those 20 minutes or so, the factory gauge needle rests as the bottom end of the red-zone. Oil pressure, if it matters in this case is damn near perfect at 40 psi at idle.
One thing I want to do is to check the engine, head, and coolant hoses with an infrared 'point-&-shoot' style temperature gauge to see what it's truly running at, but I don't have access to one at the moment.
So, what, if anything, am I missing? Any suggestions or thoughts? I know my way pretty well around these 4.0s, but this has me stumped and highly frustrated.
Last edited by onlyinajeep726; Mar 13, 2017 at 10:41 PM.
Thread Starter
CF Veteran
Joined: Apr 2011
Posts: 1,146
Likes: 0
From: Clayton, NC
Year: 1988
Model: Cherokee
Engine: 4.6L I6 Stroker with port matched +99 intake and 62mm TB
Thread Starter
CF Veteran
Joined: Apr 2011
Posts: 1,146
Likes: 0
From: Clayton, NC
Year: 1988
Model: Cherokee
Engine: 4.6L I6 Stroker with port matched +99 intake and 62mm TB
Turns out, that sending unit, despite being new, was a POS and ended up being the culprit. I replaced it with another brand, and it's working fine now. Thanks for the replies.
Newbie
Joined: Mar 2017
Posts: 4
Likes: 0
Year: 1999
Model: Cherokee
Engine: L6 4.0
Do you know what the part number was or which sending unit you changed. I'm having somewhat similar issues on my XJ.
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Thread Starter
CF Veteran
Joined: Apr 2011
Posts: 1,146
Likes: 0
From: Clayton, NC
Year: 1988
Model: Cherokee
Engine: 4.6L I6 Stroker with port matched +99 intake and 62mm TB
http://www.oreillyauto.com/site/c/de...ensor!s!sender
I've heard some hit or miss issues with it, too, but mine works.
CF Veteran
Joined: May 2012
Posts: 7,965
Likes: 964
From: Lost in the wilds of Virginia
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
The safest route is to stick with OEM sensors on these beasts. There are just too many stories of failures right out of the box with aftermarket. It's basically a roll of the dice.
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Joined: Aug 2011
Posts: 43,971
Likes: 1,579
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
CF Veteran
Joined: May 2012
Posts: 7,965
Likes: 964
From: Lost in the wilds of Virginia
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,579
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
