1999 Jeep Laredo Heat problem

1999 JEEP GRAND CHEROKEE LAREDO
120,000 MILES • 6 CYL • 4WD • AUTOMATIC
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TRUTZEL
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99 Grand Cherokee Laredo,Will only get warm,not hot enough to have to turn down.
Have manual controls.(not dual zone)
Installed a new (195) thermostat,flushed out heater core in reverse,with air and water.Bottle is full.
Temp gauge reads about 195-200.
Can turn temp dial and make it go from warm to cold.not hot.
Last summer in heavy wind I was towing a 6 x 10 inclosed trailer and it almost overheated. Only time it has ever done that.
Feb 4, 2010 at 9:30 PM
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SERVICE WRITER
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Bring the engine to temp. turn the temp to hot. Is it hot for a moment then goes cold?
IF so next feel the heater core hoses, are both hot or one cooler?

IF the latter, then pull the hoses to the heater core, fill the core with a bottle of flushing chemicals and let it set for 3 hours, then flush it again in both directions and retry.

IF the former, then post back.
Feb 5, 2010 at 5:06 AM
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TRUTZEL
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No it does not get hot then cold.It will get warm and stay there the whole time.

Thanks,Tony
Feb 5, 2010 at 3:59 PM
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SERVICE WRITER
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I worded that poorly, I apologize.

The things I think we still need to focus on is the heater core, an air pocket or a thermostat or water pump.

There are other possibllities but have to know these are right. BTW, what kind of condition was the coolant? brown? How often were flushes done?


The heater core is the highest point and any air pocket will not give you full heat. I have run into situations that a tool that pulls vacuum on the cooling system is sometimes needed. IF one is unavailable you can try to jack up front end, and fill with your funnel cold, start it up, let it warm up, while it burps the air out, then let it cool and do it again maybe 3 or 4 times, that usually will get the air out of the system.

What are the heater cores lines like. Are they both hot to the touch ?

IF they are not both hot I would now either question the new thermostat IF the engine temp does not come up within 10 minutes of idle and the cooling fan does not cycle, I would then look at the t-stat bad even though it's new...seen many out of the box that were bad.

If it does come to temp both heater hoses should be hot. IF only one is you can pull the hoses to the heater core, fill the core with a bottle of flushing chemicals and let it set for 3 hours, then flush it again in both directions and retry. It would not surprize me if the core was still coated inside and insulating the transfer of heat. IF the hoses remain this way afterwards flushing, replace the core with an OEM...not aftermarket.

IF both hoses are not hot to the touch, the engine is coming to temp, then I would question circulation.
Pull the waterpump and inspect the fins for corrosion.
Feb 6, 2010 at 5:42 AM