overheating and mysterious coolant leak on highway - JeepForum.com
 
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post #1 of 10 Old 08-06-2020, 09:51 AM Thread Starter
rattler555
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overheating and mysterious coolant leak on highway

Hello All,
Yesterday by good ole 96 XJ took a ***** on the highway pulling a trailer. Pulled the trailer many times before. Driving around 60 she overheated so I pulled over and checked things out. Coolant was everywhere but no ruptured hoses. I had it towed back home to inspect further. I started it up and let her run until reaching red temps but no leaks!!!! I did replace the water pump and t-state about a year ago with no issues until now.

Any ideas on the issue? Bad radiator?

Appreciate any feedback

Cheers.

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post #2 of 10 Old 08-06-2020, 11:07 AM
CJ7-Tim
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If your Cherokee has an automatic transmission, and you tow more than once or twice a year, it should have a transmission cooler. The AW-4 automatic transmission is well known to run warmer than most, and towing just makes it get hotter. Also, unless you are driving on flat as Nebraska highways, the transmission should be in 3rd when towing.

Until you locate the source of the coolant leak, you can't buy the correct repair parts.

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post #3 of 10 Old 08-06-2020, 01:31 PM Thread Starter
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Thanks for the info. I did notice my console would get really hot while towing. I'll look into adding some line into the tranny.
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post #4 of 10 Old 08-07-2020, 10:55 AM
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overheating and mysterious coolant leak on highway

When the Coolant gets too hot, it goes into the overflow reservoir. When it boils over, coolant will come out the vent port at the front of the reservoir. It’s happened to me on more than one occasion driving through the Rockies.

Towing wouldn’t specifically overheat the Jeep. I’ve beaten hard on the transmission and not had issues. I would suggest trouble shooting your cooling system further (coolant temp sensor, pressure cap, radiator lines, radiator) in general and also adding a Trans Cooler as added precaution.


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post #5 of 10 Old 08-08-2020, 08:34 AM
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check the core plugs under the manifolds and the pressure cap, both areas which can leak and you not see it when you open the hood. Core plugs are obviously corroded when they start to leak, pressure cap can just start to leak because it is old (easy fix)

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post #6 of 10 Old 08-08-2020, 08:36 PM Thread Starter
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Quote:
Originally Posted by radventurer View Post
When the Coolant gets too hot, it goes into the overflow reservoir. When it boils over, coolant will come out the vent port at the front of the reservoir. It’s happened to me on more than one occasion driving through the Rockies.

Towing wouldn’t specifically overheat the Jeep. I’ve beaten hard on the transmission and not had issues. I would suggest trouble shooting your cooling system further (coolant temp sensor, pressure cap, radiator lines, radiator) in general and also adding a Trans Cooler as added precaution.


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I worked on trying to reproduce the leak last night with NO avail. I added coolant to the radiator and ran the engine till she got warm. The temp hit a little over 210 then dropped back down prolly when the t-stat openned. I let it run for 10 mins in my garage with zero coolant leaks.

Can coolant leak out of the radiator cap if the temp gets too high? This would fit my scenario.
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post #7 of 10 Old 08-09-2020, 02:01 AM
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Yep, when it gets hot the pressure needs to rise or it will steam. The cap is designed to work up to 16 psi. Without the cap working the pressure will be at atmospheric and the coolant will turn to steam at 100 Celcius / 212 Fahrenheit. A 16psi/1 bar radiator cap will allow you to build pressure to 120 Celcius /248 Fahrenheit. When the reach 16psi they vent a small amount which goes to the coolant reservoir, when cold the system will suck it back in. If it reaches 120/248 it will vent a lot more including steam.

However, if the radiator cap is old the rubber sealing surfaces may not allow you to reach 16psi. It will therefore vent before it reaches 120/248 and at that lower temperature you can start to vent a lot of coolant, driven by steam created deep inside the engine.

Had this on my Cherokee a few months ago, would lose coolant and the gauge would spike due to steam. However the IR gun showed it was running reasonably normally.

I suggest you get an IR gun and check temperatures at both hoses, thermostat housing and radiator cap.

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post #8 of 10 Old 08-09-2020, 06:46 AM
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Quote:
Originally Posted by BagusJeep View Post
Yep, when it gets hot the pressure needs to rise or it will steam. The cap is designed to work up to 16 psi. Without the cap working the pressure will be at atmospheric and the coolant will turn to steam at 100 Celcius / 212 Fahrenheit. A 16psi/1 bar radiator cap will allow you to build pressure to 120 Celcius /248 Fahrenheit. When the reach 16psi they vent a small amount which goes to the coolant reservoir, when cold the system will suck it back in. If it reaches 120/248 it will vent a lot more including steam.

However, if the radiator cap is old the rubber sealing surfaces may not allow you to reach 16psi. It will therefore vent before it reaches 120/248 and at that lower temperature you can start to vent a lot of coolant, driven by steam created deep inside the engine.

Had this on my Cherokee a few months ago, would lose coolant and the gauge would spike due to steam. However the IR gun showed it was running reasonably normally.

I suggest you get an IR gun and check temperatures at both hoses, thermostat housing and radiator cap.
I'm betting the cap is bad. They don't last forever.

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post #9 of 10 Old 08-09-2020, 08:08 AM
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Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a worn out mechanical fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller, leaky frost plugs, or even a defective radiator cap. None of the cooling system parts last forever.

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others, and your engine will overheat. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic, points to a weak or failing mechanical fan clutch or worn out water pump fins.

The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.


-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.
-Inspect all of the frost plugs in the block and the ones on the backside of the head for rust holes and coolant leakage.
-Use a chemical flushing/cleaning solution to remove mineral buildup or rust, flush with clean water, and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a genuine Jeep 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out radiator cap will allow not hold system pressure which can cause boil overs and/or allow the coolant flash over into to steam. You will likely see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.

If you have covered all the points listed above and still have overheating issues, inspect and test the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here –

http://www.offroaders.com/tech/engine-overheating.htm

http://www.carparts.com/classroom/coolingsystem.htm




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post #10 of 10 Old 08-12-2020, 07:35 AM Thread Starter
rattler555
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Guys, thanks for all the great feedback. I'm going to replace the cap and perform a thorough flush. Then see where she takes me! Appreciate the insight.
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