Stumped With Cooling System Problem

[macleanflood]

My 4.0L doesn’t have the service port

Grab one of these...Racetronix sells then too but they're out of Canada....

https://www.amazon.com/GlowShift-Di...pter-Fitting/dp/B0GCP19ZP9?tag=wranglerorg-20

Then you'll need an 1/8" npt to Schrader...

https://www.amazon.com/GODESON-Valv...r-Compressor/dp/B0CPPG2KKS?tag=wranglerorg-20

-Mac

 

[Mud Mixer]

How is your ignition timing?
Seems you've covered the mechanical bases.

 

[macleanflood]

How is your ignition timing?
Seems you've covered the mechanical bases.

Ignition timing is set by the PCM.

-Mac

 

[Link]

What are the ACUTAL engine temps?

How have you determined the engine is overheating at idle? Not saying you are wrong but you are throwing parts at it and I haven’t yet heard how you have decided it’s overheating.

 

[Mud Mixer]

Ignition timing is set by the PCM.

-Mac

So there's no need to check or verify the timing, the PCM is 100% foolproof.
Got it.

 

[Link]

So there's no need to check or verify the timing, the PCM is 100% foolproof.
Got it.

How do you plan to check and adjust it?

 

[macleanflood]

PCM is 100% foolproof.

Well, I wouldn't go that far...a custom tune will get you something...these were mostly tuned by the factory for emissions...but so far as this topic...doubt it's causing the problem.

-Mac

 

[Slipstreak]

Alright I managed to get some more work done and here’s what I found:

1.) Sensor that controls the temp reading on the dash for the most part was pretty accurate. Temps measured with a temp gun closely correlated and would rise as the temp slowly crept at idle and would often exceed 220*

2.) For the sake of simplicity, I opted to do another flush on the cooling system and found quite a bit of sediment. (See attached photo). I proceeded to keep flushing several times and the sediment kept coming. Failing heater core? With all the major cooling components being new and a completely overhauled 4.0 this is the only thing I could think of. If the heater core is falling apart would this theoretically keep happening until I replace it and flush the system till clear? Or should I just keep flushing until the system is clear even it takes dozens of flushes?

Curious to know everyone’s thoughts. I’m not entirely sure if this could be causing my Jeep to overheat at idle and is just one of those things I need to take care of as regular maintenance.

 

[macleanflood]

The overhauled 4.0 could have been full of junk and never properly cleaned out by the engine builder.

I doubt it's coming from the heater core...but anything is possible.

You can speculate about it forever but it sounds like you're on to something. I'd keep flushing the system until it's clean.

-Mac

 

[JKP]

You can flush just the heater core, forwards and backwards.

You can bypass the heater core while flushing the engine.

If you really want to do down the flushing rabbit hole, remove the block drain plug. You'll need a 5/16 pipe plug socket. Maybe the rebuilder had it out and it's not rusted in place.

 

[WVJeep304]

Maybe bypass the heater core and see if the problem persists?

This is easy and free... I'd try it. Not saying it will fix your problem, but it'll rule the heater core in or out as an issue. If it seems to be the issue, you can then attempt to flush it if you want, or if it seems too far gone, you just replace it.

 

[mrblaine]

So there's no need to check or verify the timing, the PCM is 100% foolproof.
Got it.

The PCM compensates about 10 degrees either side of 0 with no ability to change the timing much other than to synch the cam and crank sensors to as close to 0 as possible. In short, the engine will not run any differently in any way whatsoever with it set at -10, +10, 0, or anywhere inbetween. So no, if it runs down the road, there is no need to check the timing.

 

[KennethS]

if it seems too far gone, you just replace it.

Or bypass it.

 

[mrblaine]

Alright I managed to get some more work done and here’s what I found:

1.) Sensor that controls the temp reading on the dash for the most part was pretty accurate. Temps measured with a temp gun closely correlated and would rise as the temp slowly crept at idle and would often exceed 220*

2.) For the sake of simplicity, I opted to do another flush on the cooling system and found quite a bit of sediment. (See attached photo). I proceeded to keep flushing several times and the sediment kept coming. Failing heater core? With all the major cooling components being new and a completely overhauled 4.0 this is the only thing I could think of. If the heater core is falling apart would this theoretically keep happening until I replace it and flush the system till clear? Or should I just keep flushing until the system is clear even it takes dozens of flushes?

Curious to know everyone’s thoughts. I’m not entirely sure if this could be causing my Jeep to overheat at idle and is just one of those things I need to take care of as regular maintenance.

View attachment 702819

Running water through it is not a proper flush. You need something like the Prestone drive around flush or similar.

 

[MikeE024]

Alright I managed to get some more work done and here’s what I found:

1.) Sensor that controls the temp reading on the dash for the most part was pretty accurate. Temps measured with a temp gun closely correlated and would rise as the temp slowly crept at idle and would often exceed 220*

2.) For the sake of simplicity, I opted to do another flush on the cooling system and found quite a bit of sediment. (See attached photo). I proceeded to keep flushing several times and the sediment kept coming. Failing heater core? With all the major cooling components being new and a completely overhauled 4.0 this is the only thing I could think of. If the heater core is falling apart would this theoretically keep happening until I replace it and flush the system till clear? Or should I just keep flushing until the system is clear even it takes dozens of flushes?

Curious to know everyone’s thoughts. I’m not entirely sure if this could be causing my Jeep to overheat at idle and is just one of those things I need to take care of as regular maintenance.

View attachment 702819

Using a gun that pulsates hose water with about 10 psi of compressed air works exponentially better than only flushing with water on a compromised cooling system. I have way more experience on this topic than I'd prefer. It's alarming how much more will come out of the heater core, radiator, and block (I flushed all separately into a clear tote using hoses for evaluation). About 20 gallons in, the heater core released an alarming amount of crud that was packed in there and had not come out after many normal flushes over the years (it was disturbing).

https://www.amazon.com/dp/B000F5ECRW?tag=wranglerorg-20

 

[GregBelleville]

Using a gun that pulsates hose water with about 10 psi of compressed air works exponentially better than only flushing with water on a compromised cooling system. I have way more experience on this topic than I'd prefer. It's alarming how much more will come out of the heater core, radiator, and block (I flushed all separately into a clear tote using hoses for evaluation). About 20 gallons in, the heater core released an alarming amount of crud that was packed in there and had not come out after many normal flushes over the years (it was disturbing).

https://www.amazon.com/dp/B000F5ECRW?tag=wranglerorg-20

Here's a link to a post about the crap that came out when I flushed my heater core. It's definitely worth doing.

https://wranglertjforum.com/threads/heater-core-flush-satisfying-results.75980/

 

[GoldenGorilla]

The heater core does not make sense as the source of overheating unless it is losing pressure through it. You should smell coolant inside. But this could definitely trigger an overheat.

The debris inside the core should backflush out. If it is circulating, is likely also on to top side of the radiator.

Severe duty clutch is usually better to resolve low speed issues as it has a higher lock % but typically lower unlock %.
Typical Severe = 20-25% / 80%
Typical HD = 25-30% / 70%

 

[WVJeep304]

The heater core does not make sense as the source of overheating unless it is losing pressure through it. You should smell coolant inside. But this could definitely trigger an overheat.

I only brought it up because I'm personally aware of an instance 10 or so years ago where a friend (that did ZERO preventative maintenance, and barely did required maintenance/repairs) was having an overheating issue. Ended up everything in his cooling system checked out fine or was replaced, but his heater core was so corroded & obstructed, it was still allowing coolant through but majorly limited the flow.

I would have halfway expected the heater core to bust/spring a leak under those conditions, but halfway wonder if the buildup didn't actually add some structural integrity to keep that from happening.

 

[MikeE024]

I only brought it up because I'm personally aware of an instance 10 or so years ago where a friend (that did ZERO preventative maintenance, and barely did required maintenance/repairs) was having an overheating issue. Ended up everything in his cooling system checked out fine or was replaced, but his heater core was so corroded & obstructed, it was still allowing coolant through but majorly limited the flow.

I would have halfway expected the heater core to bust/spring a leak under those conditions, but halfway wonder if the buildup didn't actually add some structural integrity to keep that from happening.

I ran hose water through both ends of the heater core. Back flushing did the most, but it also needed flushed the other way after things were loosened up. I went back and forth twice to make sure I got it all out. I did the same with the radiator and drained the block (some plugs are too rusty or seized to remove). I then ran Thermocure in the system for multiple days.

If someone is only removing surface rust and smaller bits of stuff in the system, then they could simply drop the fluid and run Thermocure for a few days since a lot of the little stuff will come out as you drop the Thermocure/water multiple times.

 

[Intimnasc]

So I chased a similar problem with slight overheating and some backfiring through the intake at low rpms when accelerating. Mine turned out to be the bank 1 sensor 2 O2 sensor. I didn't see it until I hooked up a scan tool and charted it for a while. There were no codes but the one sensor was flat lining causing the computer to run the jeep lean. Another indicator of the lean condition that was only seen on the scan tool was the calculated catalytic converter temperature. In the computer there is a calculation that shows cat temp but since it is a calculation and not an actual sensor its not totally accurate. Have you hooked a scan tool up that can chart and read all the sensors on the motor?