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Overheat at Idle

iwannadie said:
Worst case you confirm water in your oil or best you blew money on fresh oil confirming its good.
Click to expand...

Ya, that's what I'm thinking. I'm going t replace the radiator, water pump, tstat, and hoses just for good PM. They're all bone stock, and it's a 2001.

I guess I'll wait and see what the test results show as to my next step to take.



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I feel your pain I'm in the same boat only I run hot while driving not just at idle. I'm also doing a wholesale change and replacing it all too.

I'd strongly recommend a hesco water pump, my last one went about 8 years before leaking.
 
TheSloMoShow said:
Ya, that's what I'm thinking. I'm going t replace the radiator, water pump, tstat, and hoses just for good PM. They're all bone stock, and it's a 2001.

I guess I'll wait and see what the test results show as to my next step to take.



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Click to expand...

Sounds like a good plan. I don't think the part you are looking at in those photos could leak coolant. It looks like the top of the valve stem guide area and the rocker arm. You would need to pull the cover to see the typical crack areas.

If the e-fan is working and turning on the correct temps and the fan clutch is working to specs, the water pump or radiator must be the problem (99% probable) if there is no slow coolant loss.

Only other times I had idle over heating issue was if the engine was running too lean (O2 sensor issue), Exhaust leaking and blowing on the block, or AC was having an issue, or there was a coolant leak somewhere, bad Radiator cap, bad seal, needs to be air tight, between the radiator and over flow bottle.

Oh and trash in fins of the condenser and radiator can do it too.
 
Well, this is irritating. I replaced last night the radiator, tstat, tstat housing, overflow tank, cap, water pump and all hoses except heater hoses.

And as of this morning, still overheats at idle 😤.

So, I'm now starting to think running lean is more probable.

I'll be testing the O2 sensors here in the next day or two. As of this morning, using DashCommand, LT Fuel trims are at 10%. Either they engine truly is running too rich, or the O2 is giving bad readings and my engine was operating normal but now is way too lean.

On a side note, what are other potential causes of running lean aside from bad O2 sensor?

I did replace all 6 injectors in March with reman Bosch 4-hole. I bought them on eBay from dimarmotorsports. I don't know what their flow rating is. Maybe this has some effect, or I would assume also a bad pressure regulator in the fuel tank?


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I went through all of this a while back with a four cylinder, even fixed my clutch with sheet metal screws, and it still overheats at idle. I came to the conclusion that it's the condenser obstructing air flow.

Of course, mine only does it after idling in 100°+ for five minutes on max AC, not so much without air conditioning. It can be pretty frustrating, especially when you have it overcooling during all other kinds of operation.
 
Overland said:
I went through all of this a while back with a four cylinder, even fixed my clutch with sheet metal screws, and it still overheats at idle. I came to the conclusion that it's the condenser obstructing air flow.

Of course, mine only does it after idling in 100°+ for five minutes on max AC, not so much without air conditioning. It can be pretty frustrating, especially when you have it overcooling during all other kinds of operation.
Click to expand...

I'd like to think the same, but the Jeep operated at one point efficiently with the condenser in it's current spot - now it doesn't.

If the engine truly is running lean then:

a) The O2 sensors are reading the fuel mixture erroneously as rich, and trimming fuel causing a lean mix instead of optimal mix.
Fault = bad O2 sensors.

b) Unregulated air (additional) is making it into the system.
Fault = ???

I can check the O2 sensors, it just scares me that if they check out OK then I'm really out of options.

Since it bothers me that the current coolant temp sender gauge is aftermarket and not OEM, I went ahead and bought a Mopar sender gauge to install into the system tomorrow. I should have done this yesterday, but it bothers me thinking "what if" that was somehow the issue...
 
Last edited:
Yep, so did mine. Everything was new, when it was new.

If you can see through it to the fan and it's not full of bugs and small rocks like mine is, or the fins haven't been rolled over by pressure washing, it's not likely the problem.

I flushed the block when I replaced freeze plugs, leveled the manifold, changed temp sensors, radiator, fan clutch, NTK O2s, combed the condenser, fixed the exhaust, bumped idle speed with a jumper, adjusted the AC charge, replaced the fuel tank, pump, screen, and filter.

All that's left is crud in my condenser fins.

For what it's worth, your O2s should indicate a lean condition if present. Maybe unplug the HVAC source and go for a drive. See if it registers as such.
 
By unplugging that vacuum line you're creating a lean condition, and driving it should register as such. In other words, your computer should register a lean condition and relay that information to you after a short drive. If the computer registers a lean O2 code, but didn't before, then I don't think a minute vacuum leak is your problem.

I would not suggest that you unplug the power brake booster and go for a drive, but if you pull that line in the driveway, it should idle way up, and it shouldn't take much running like that to register a code, either.

tl;dr the computer should indicate a lean condition if it is indeed present.

I've experienced fuel starvation from the same problem more than once and one registered a lean code while the other didn't. Your results may vary.
 
I finally installed the last bit of the cooling system today, OEM sender gauge. And still, it's overheating a bit at idle. Not cooling like it should be.

So, I'm now pretty positive that since the cooling system is up to snuff that there must be an issue with operating condition (running lean).

I pulled the HVAC/cruise/4x4 vacuum fitting from the manifold and drove around for a bit, no CEL.

Meanwhile, my LT Fuel trims are still -11 to -12%.

Wouldn't this indicate a rich condition, the exact opposite of what we were all thinking was the culprit (lean condition)?

I still have yet to test all 4 O2 sensors, but am trying to wrap my head around why the Jeep seems to be running rich and not lean according to the O2.

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I can't say about the -11 to -12% readings, but if the computer thinks it is running rich from the data, it may using the rich reading data to try and run it leaner, and then O2 sensor-wiring system is giving the computer bad data saying it did not switch to lean enough, so the computer keeps trying. It the tech world-lab data it is called skewed data IIRC. You need to test the data at the sensor itself and compare to the data at the computer. If the disagree you have a clue. If they agree you have a fuel leak into engine that the computer can not control. Also consider that the O2 sensor could be bad even if the O2 sensor data at the sensor and at the computer match. So you do not get a single possible problem yet. Wiring could have a bad connection too between the sensor and the computer!!!! Does the OBD-II show 2 banks of data???? It should if there are 4, O2 sensors? That could narrow it down to 3 cylinders. If both banks have the same issue with O2 data, then look for a vacuum leak causing the excess air that makes it run lean. A vacuum leak would run it lean and make the computer try to compensate with a richer fuel trim, but at idle the computer tries to keep the idle where it belongs if it can and thus may not add enough fuel to avoid running the idel too high and causing other problems.

Running rich would not make it run hot!!!!!!

I do not know if the - versus + fuel trim means lean or rich. Sorry.



TheSloMoShow said:
I finally installed the last bit of the cooling system today, OEM sender gauge. And still, it's overheating a bit at idle. Not cooling like it should be.

So, I'm now pretty positive that since the cooling system is up to snuff that there must be an issue with operating condition (running lean).

I pulled the HVAC/cruise/4x4 vacuum fitting from the manifold and drove around for a bit, no CEL.

Meanwhile, my LT Fuel trims are still -11 to -12%.

Wouldn't this indicate a rich condition, the exact opposite of what we were all thinking was the culprit (lean condition)?

I still have yet to test all 4 O2 sensors, but am trying to wrap my head around why the Jeep seems to be running rich and not lean according to the O2.

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Click to expand...
 
The negative fuel trim indicates it's reducing fuel supply, i.e. it thinks the engine is running rich. Which is odd, since we would think the overheating is due to the opposite - a lean condition.

I definitely need to test the O2 sensors next, but if the test data and computer agree it doesn't mean I'm off the hook. The computer could be reading the sensor correctly, but it's the sensor itself that's not working correct as you said.

I'm almost tempted to just replace all 4 sensors anyway.

I'll see what the O2 sensor readings turn up this weekend.

Btw, I got th oil sample shipped out yesterday. Fingers crossed the results come back with no water/antifreeze in my oil.

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The old style green antifreeze has silicates (oxidized silicone), so if the O2 sensor has seen a fair amount of that type of antifreeze leak into the exhaust it could have pushed them over the edge, contaminated the sensor catalyst, if they are not already just worn out. If there is a coolant leak into the exhaust the cat converters will clog up next.
 
gradon said:
Compare the LTFTs from both banks.


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Click to expand...
Unfortunately it isn't broken out by bank. On DashCommand that is.

I may need to actually bring out the diagnostic tool, I think that gives data between the two.

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