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Unread 11-02-2013, 11:46 AM   #1
Robert1964
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Help!!! Over heating 4.0 Grand Cherokee

I'm brand new to this forum and I'm looking for help. I have a 99 Grand Cherokee 4.0 that is over heating. New fan and relay and radiator recently installed. Drove it a couple weeks with all these new parts with no problem. All of a sudden, it over heats. Fan is running fine and when I opened it to replace the thermostat, it did not even have one. I've put a thermostat back in it and when you crank it it runs great. No water in the oil. But when you crank it, the temperature rises and never stops. Is this a blown head gasket or possibly something else.

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Unread 11-02-2013, 01:12 PM   #2
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Try burping the radiator (although the fact that it was fine for a couple weeks AFTER the radiator replacement wouldn't seem like this would be the problem) If you do see a lot of air bubbles replace radiator cap too if radiator didn't come with one.



Maybe your heater core's clogged up although this shouldn't cause major overheating like you're getting.
Get any piece of pipe with the inside diameter of your heater core hoses and bypass your heater core (join hoses together) and see what the needle does.
Any large hardware store (Home Depot / Lowes ) should have something to fit that bill....plumbing department: pvc,galvanized, or copper pipe...etc..
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Unread 11-02-2013, 02:29 PM   #3
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Thanks....I'll try burping it....been sitting a while now so I'll have to charge the battery. But its worth a shot.
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Unread 11-02-2013, 02:30 PM   #4
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Possibly a bad new thermostat or installed wrong. I would pull it again and see what happens.
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Unread 11-02-2013, 02:52 PM   #5
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Possibly a bad new thermostat or installed wrong. I would pull it again and see what happens.
Yep...could be...take it out and boil it on your stove...
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Unread 11-02-2013, 03:30 PM   #6
Robert1964
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It was overheating without any thermostat in it at all......I've put a 180 thermostat in it myself and yes its in the right way.....LOL....made that mistake once as a teenager and make sure these days not to do it again.
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Unread 11-02-2013, 04:41 PM   #7
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It's a possibility that you have a busted water pump. It's the only thing left untouched correct?
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Unread 11-02-2013, 06:05 PM   #8
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Quote:
Originally Posted by Robert1964 View Post
It was overheating without any thermostat in it at all......I've put a 180 thermostat in it myself and yes its in the right way.....LOL....made that mistake once as a teenager and make sure these days not to do it again.

Sorry I did not pick up on that it was overheating before. Like MuddyWJ said, check your water pump.
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Unread 11-02-2013, 06:28 PM   #9
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It's a possibility that you have a busted water pump. It's the only thing left untouched correct?
I was thinking that too..but usually they start leaking profusely out the weep hole..and I assume he hasn't noticed any leaks/coolant level drops.
Possible the shaft broke between pulley and impeller...but not common.


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It was overheating without any thermostat in it at all..
I realized that you had stated that after my last post...had a little brain slip.
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Unread 11-02-2013, 08:30 PM   #10
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I was thinking that too..but usually they start leaking profusely out the weep hole..and I assume he hasn't noticed any leaks/coolant level drops.
Possible the shaft broke between pulley and impeller...but not common.
I was thinking more like the impeller itself is broken. Correct me if I'm wrong but aren't they plastic from the factory.
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Unread 11-03-2013, 04:20 AM   #11
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I was thinking more like the impeller itself is broken. Correct me if I'm wrong but aren't they plastic from the factory.
I don't know about factory, but one I got from NAPA was and disintegrated the impellers after about 3 years. Started to overheat when driving 60MPH then would cool when idling. No blades left on the pump.
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Unread 11-03-2013, 12:21 PM   #12
Robert1964
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Thanks.....I'll check the water pump first chance I get.......I've never had one loose the impellers but if they are made of plastic, then thats a real possibility.....All my water pumps (on other vehicals) have started leaking out the weep hole first. I will be pulling the pump after hearing this. Its the only thing I have not checked. Thanks for the info and any more info will be greatly appreciated.
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Unread 11-03-2013, 01:30 PM   #13
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The plastic impeller cut loose on mine a few years back. It wasn't until after replaced the radiator and thermostat, that I figured out what was going on. This is not your typical leaky seal type water pump failure. In this failure nothing leaks the impeller simply breaks loose from its shaft and no longer circulates coolant.
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Unread 11-03-2013, 02:42 PM   #14
Robert1964
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Now I'm really suspecting the water pump after hearing this......I'll be pulling it tomorrow......Anyone else had this issue? I'm so hoping this is the problem and not a head problem.
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Unread 11-03-2013, 08:06 PM   #15
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Quote:
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Now I'm really suspecting the water pump after hearing this......I'll be pulling it tomorrow......Anyone else had this issue? I'm so hoping this is the problem and not a head problem.
I doubt that a busted head gasket would cause overheating; it's the other way around. Now once it gets to operating temperature and the thermostat opens, grab the upper hose (a good idea to wear gloves), you should feel it is under pressure. If that's not the case, that could be a sign the water pump is gone.

IMO it's either the water pump or the CTS is giving you a wrong reading (in that case it's not overheating). You might want to get one of those IR thermometer and check the actual temperature at the thermostat housing and compare to the gauge reading on your dashboard.
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