Cooling system problem - JeepForum.com
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post #1 of 7 Old 01-07-2020, 10:40 PM Thread Starter
Aussides
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Cooling system problem

My 1999 Jeep Cherokee XJ with the 4.0 l6 was running fine with a leaky water pump so I proceeded to replace the water pump and the coolant the next morning I blew the bottom hose off of my radiator and I thought maybe I didn’t tighten it enough but with more work and trouble shooting it seems my Jeep will run fine with the heater on but when the heater is turned off the cooling system starts to build lots of pressure and blows smoke and antifreeze out of the cap

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post #2 of 7 Old 01-07-2020, 10:43 PM Thread Starter
Aussides
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But the Jeep never got hot until stopping and turning it off so I don’t think I blew a head as it never went above 220
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post #3 of 7 Old 01-08-2020, 08:15 AM
JWELK
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Something makes little sense. The heater core always has water flowing through it. The only difference is air passes over the core and into the cabin. It seems as if the heater is acting as the radiator. Meaning the radiator is restricted, try a Blue Devil flush.
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post #4 of 7 Old 01-08-2020, 08:34 AM
jtec
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keep old water pump.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 7 Old 01-08-2020, 09:07 AM
CJ7-Tim
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I would say you are not done with your cooling system overhaul and maintenance. Does your Jeep have a coolant overflow tank, and is the hose for it clogged ?


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 slipping 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.

The cooling system is a group of interrelated 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 –
 
www.offroaders.com/tech/engine-overheating.htm
www.carparts.com/classroom/coolingsystem.htm
 

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post #6 of 7 Old 01-08-2020, 11:27 AM
car6car
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Clogged radiator (and everything else) can be diagnosed with laser thermometer.

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post #7 of 7 Old 01-14-2020, 08:53 AM
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Quote:
Originally Posted by Aussides View Post
My 1999 Jeep Cherokee XJ with the 4.0 l6 was running fine with a leaky water pump so I proceeded to replace the water pump and the coolant the next morning I blew the bottom hose off of my radiator and I thought maybe I didn’t tighten it enough but with more work and trouble shooting it seems my Jeep will run fine with the heater on but when the heater is turned off the cooling system starts to build lots of pressure and blows smoke and antifreeze out of the cap
I hope you fixed it by now. Did you change the thermostat and buy a quality water pump? Turning on the heater allows the hot water and coolant to enter the heater core. The heater core is really just another radiator designed to extract the heat in the coolant and pass it on into the air surrounding it, in this situation the driving compartment, thus dropping the temperature of the coolant, thus cooling the over heating engine.

Quote:
Originally Posted by jeepinmichguy_ View Post
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