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Old 04-05-2013, 12:15 PM   #1
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Running hot, new water pump and thermostat

I recently swapped a rebuilt 4.0 into my jeep. When I fired it up for the first time, the temp gauge shot to 250 in about a minute within starting. I have electric fans and both were on.

The thermostat is new, but what else could cause this problem? Could the gauge be bad? If so, how would I test it?
Other than that, it ran like a top.

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Old 04-05-2013, 12:26 PM   #2
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You need to bleed the air out of the system...

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Old 04-05-2013, 12:31 PM   #3
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we had to replace radiator it was plugged up
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Old 04-05-2013, 12:33 PM   #4
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How do I bleed the air out?

I just pulled the thermostat housing. It was dry as a bone. The thermostat was sopping wet on te head side and dry on te housing side.

Bad thermostat?
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Old 04-05-2013, 01:25 PM   #5
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yes, your thermostat is sticking for sure if its dry on the other side of it.

Put it in a pot of boiling water with a meat thermometer. It should open at like 180, 190 or 210 depending on its rating.
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Old 04-05-2013, 02:07 PM   #6
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Old 04-05-2013, 02:31 PM   #7
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Upside down?
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Old 04-05-2013, 08:46 PM   #8
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Quote:
Originally Posted by RednekYJ View Post
You need to bleed the air out of the system...
No, 4.0s bleed themselves. If you notice they are mounted at "nose up" angle and this allows the air bubbles to gradually travel to the radiator cap and through the tube into the reservoir. I thought the same thing for awhile but its a common misconception.

But for the OP question. Before you start swapping parts out I would get a infrared temperature gun ($30 Harbor freight) and point it at the head to see if you actually are overheating. If the gun reads a normal temp then chances are the your temp sensor in the back of the cylinder head has retired. $10 on Quadratec $8 at Advance Auto. i prefer the Quadratec one but thats just me

But if the the temp gun tells you you are overheating...
1. do you hear any boiling int he radiator when the gauge says 250?

2. Are the hoses scalding hot and rock solid when the gauge says 250?

3.Check to make sure your thermostat works (i know u said its new but thermos are notorious for being faulty even when there new) as the engine warms up firmly hold the upper radiator hose its should feel cool until the gauge hits 195 and them you should feel it get warm (the thermostat just opened). Or you can take it out and put it in a pot of boiling water to see if it opens. Chances are this is your problem.

4. Did you get the right water pump? You need a reverse one....make sure its a reverse one...it should have had a "R" stamped on the pump blades when it was installed.

5. Head gasket/warped head: Have you noticed any loss of coolant? Do u smell coolant while the engine is running (smells like syrup). Check remove your spark plugs and check them for inconsistent coloring (one will look way different you cant miss it). Rent a head gasket leak kit with indicator fluid from Autozone and test for hydrocarbons in you radiator (exhaust leaking into coolant pathways result of faulty head gasket or warped head).

Check what you can and let me know what happens

I had an over heating problem last year.

Good luck man
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Old 04-05-2013, 10:44 PM   #9
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I used a direct replacement water pump for my engine, which was in a 1992 cherokee. It looked just like the one I replaced. Is there a way to check it while its installed?

I am going to try a new thermostat tomorrow.

The temp sensor is brand new.
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Old 04-05-2013, 10:49 PM   #10
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When you install the thermostat, do 2 things first:

1. Test it in a pot of boiling water.

2. Drill a small pinhole in the flat disk surface to allow air to bleed out from behind. Orient this pinhole towards the top.
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Old 04-06-2013, 09:16 AM   #11
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Quote:
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When you install the thermostat, do 2 things first:

1. Test it in a pot of boiling water.

2. Drill a small pinhole in the flat disk surface to allow air to bleed out from behind. Orient this pinhole towards the top.
x2

No theres no way check the pump while its installed but if it came off another 4.0 you should be fine. I bet its the thermostat
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Old 04-06-2013, 09:30 AM   #12
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I tried a new thermostat, and its still running hot.

I just had water in it, though because I had been chasing a leak. Could that matter? I'm putting coolant in now.
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Old 04-06-2013, 09:31 AM   #13
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1994jeepyj says you have a self bleeding cooling system.... Xpress says to drill a hole in the Tstat. Who to believe and what to do????. Internet forums are great.
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Old 04-06-2013, 12:59 PM   #14
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My money is that you have air in the system.. and as already stated it need burped.. to burp it..Now if you want to run a check to make sure the whole system is clear.. hook it all back up with out the thermo stat..It show run very cool in this condition. Also one other thing to check.. is the coil spring in the lower hose in place...
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Old 04-06-2013, 01:31 PM   #15
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I dont know about the coil spring. it very well could NOT be in place since I don't know what it is.

Are you talking about the hose running from the radiator to the water pump?
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Old 04-06-2013, 01:38 PM   #16
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Other thing, while I was just running water in it, there wasn't a full two gallons. Could that have caused it to overheat?

This evening I am going to test the thermostat and put all new coolant in. I am also going to bleed the air.

I am tempted to leave the thermostat out, but I am sure it's something else since I've had it happen with two new thermostats.

Are there any negatives to running without a thermostat other than not having a heater? I'm in texas, so heaters aren't used much.
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Old 04-06-2013, 04:38 PM   #17
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Quote:
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1994jeepyj says you have a self bleeding cooling system.... Xpress says to drill a hole in the Tstat. Who to believe and what to do????. Internet forums are great.
Air can leave the the system when the thermostat opens. By drilling a small hole in the thermo you allow the air to escape before the thermostat opens which is fine and helps with the self purging process. There are no contradictions between the two posts.

As for running with no thermostat its fine, and will help you eliminate the thermostat as the culprit.

Also water is fine to use for test purposes so you dont keep spending money on coolant.

Lastly, are you positive you are overheating? besides the gauge do you see symptoms of overheating? These will include Rock solid scalding hot hoses, boiling noises, sometimes knocking.

If the jeep is actually overheating, seriously look into the possibility of a head gasket problem cause it sounds like you have covered everything else.

Edit: i forgot to mention a possible clogged radiator. Do you see crud in there? lightly touch different areas of the radiator after the jeep is up to temp, do you feel "cold" spots? if so your rad could be clogged.
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Old 04-06-2013, 06:15 PM   #18
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Head gasket is also brand new and shouldn't be the culprit either.

Whenever I pull the therm housing the head has plenty of coolant and the housing is dry. Seems to be the t stat. Maybe incredibly unlucky
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Old 04-06-2013, 06:33 PM   #19
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if the head is warped/cracked it won't matter that the gasket is new.
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Old 04-06-2013, 06:38 PM   #20
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not to give you more to wonder about.. but when the "new" engine was installed did the electric wires get pinched? you could have the gauge grounded out. you said your fans were on. did they come on instantly and stay on or do they wait and then come on when the temp hits where they are supposed to come on? do they go off or stay on constantly?
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Old 04-06-2013, 06:48 PM   #21
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I've got a manual switch for the fans. The thermostat for them is not working for sure. They are completely seperate of the rest of the vehicle.

It very well could be something like a bad gauge wire
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Old 04-06-2013, 07:51 PM   #22
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I put the therm housing on without the t stat. Gauge still shot up to hot in a hurry.

Engine doesn't feel hot. I can touch every part but the exhaust and its cool to te touch.

Now I'm thinking the reason the housing had been dry is because the engine hasn't gotten hot enough yet to open the t stat.

I feel like the gauge may be bad.
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Old 04-06-2013, 08:20 PM   #23
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Alright. I bought an infrared thermometer and te thing never got close to over heating.
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Old 04-06-2013, 09:39 PM   #24
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did you check the sending unit on the back of the motor, top, drivers side?.....that's the one for the gauge.....
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Old 04-06-2013, 10:38 PM   #25
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Alright. I bought an infrared thermometer and te thing never got close to over heating.
Cool. At least now you have peace of mind. Its definitely ether the sender, wiring, or the gauge itself. I believe that sender is directly wired to the gauge so maybe trace the wire and see if it got crushed or something
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Old 04-06-2013, 11:17 PM   #26
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I'm sticking with air in the system until further simpler troubleshooting is done.



The temp sender for the gauge is known as a "TURD" sender. Temperature Up Resistance Down. You can test this by shorting the wire at the sender to ground. Your gauge should go to full deflection. If it doesn't, then either the gauge or wiring is at fault. If it does, then either the sending unit is at fault, or your temp reading is real. You could have a t-stat installed that is not the correct 195 degree oem stat.

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