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Old 04-05-2012, 01:44 PM   #1
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still overheating and i changed everything. so frustrated.

1994 4.0yj
new:
radiator
waterpump
thermostat
spark plugs
fan clutch works fine
flushed it a million times
refilled and burped the system
no oil in coolant or coolant in oil
no leaks.

when i let it idle the temp creeps up to right befor the red...rarely touches it tho. it settles right befor it and fluctuates right round there.

here are my thoughts..tell me what u think any input would be great:

1. the coolant passages in my engine are clogged??

2. could it be my temp sensor is bad? im runnin straight water for these tests and i never hear water boiling or anything...it should be boiling at the temperature right?

3.other thought is maybe my spark plugs are the wrong kind?..

thanks i really dont know what to do at this point...

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Old 04-05-2012, 01:49 PM   #2
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My TJ is having a similar issue. The temp gauge dips all the way down into the red and moves back to normal after about 30 seconds. I've changed the thermostat with no improvement, but others are telling me that it may be the coolant sensor. I am going to try that next.

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Old 04-05-2012, 01:52 PM   #3
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A) you might not be getting all the air out of the cooling system.

Or.

B) I would still have your head gasket checked, could be leaking into the cooling system enough that the cylinder pushes compression into the cooling system, but the coolant pressure is not strong enough to push water into the combustion chamber.

If you live in an emissions state, have your local test and repair shop check the cooling system for HCs (unburned fuel).
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Old 04-05-2012, 01:56 PM   #4
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I recently installed a new thermostat in my truck, and the first few weeks it would creep up to almost the red, then settle back down to normal operating temperature. after a few weeks its not doing it any more. It could just need to be "worked in", although why, I don't know. As long as you aren't actually over heating I would let it go for a week, but just keep an eye on it.
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Old 04-05-2012, 02:08 PM   #5
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so how can i be sure to get all the air out? is there like a proper way to get it out?
right now i just let it run with the cap off and let it bubble out...
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Old 04-05-2012, 02:10 PM   #6
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Are you sure your guage is correct?

Did you verify that coolant is passing through both hoses?

Mr. Gasket 2470S - Mr. Gasket Thermocap Radiator Caps - Overview - SummitRacing.com







This cap above is a good way to see your actual coolant tempature in the radiator opposed to the tempature of the coolant in the block.

Looks like the only things you have not replaced is the tempature sending unit, tempature gauge, and hoses.

My temp. guage was messing up in my 89, it was the wire on the sending unit had become loose and corroded. I cleaned is up good and problem solved.

Another thing I have seen is, that its not terribly uncommon to get a thermostate out of the package thats bad. I had this happen to me on my 2000 Explorer once. Now I make them with a sharpy and put them in a pot of boiling water until they open to verify they work.
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Old 04-05-2012, 03:09 PM   #7
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back to the old farmer's method

When the engine is up to full operating temperature and the tstat is open, you should be able to hold the upper radiator hose lightly but not be able to hold it tight. If you can't hold it lightly, then it is likely overheating. If you can hold it lightly, it is safe to drive.

Check the heater hoses. If it is hot returning to the block with the heater on full, then you are getting flow through the heater core and the water pump is working. And also, there is no air in the system.

If you want to check the head gasket, open the radiator cap and let it come up to temperature. If the head gasket is bad you will get bubbling in the radiator.

Hands and eyes are still one of the best guages.

If you want to check the tstat, just put it in a pan of water on the stove and watch it heat up. As the water just about comes to a boil the tstat should start to open. If the water boils and it doesn't open, then it is bad.

If it opens too soon and it takes too long to boil the water after the tstat opens it is opening too soon.

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Old 04-05-2012, 03:13 PM   #8
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Old 04-05-2012, 09:32 PM   #9
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Man IDK about all that hold your hand on something that should be 200+ deg. are spending money on all kinds of tools, BUT if you have a good cap thats 14pis plain water won't boil till about 230 +or- the psi, so no it should not be boiling when the stat opens are for a lot hotter, you have spent that much a sending unit is not much more. If it Ain't boiling over, RUN IT!
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Old 04-05-2012, 10:23 PM   #10
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guys...it was the temp sending unit. yea a freakin $11 part the whole time. god i feel like an idiot for not tryin that first. thanks for the input tho

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