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Unread 11-07-2012, 09:04 PM   #1
Nic
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New Headgasket Overheating!

I just finished replacing my headgasket with a new MLS one in my 4.0L. Now that its all back together I fire up the Jeep and everything seems to be fine. But the temperature gauge steadily climbs right to the red line (around 120 or something) now. I also had to replace my coolant temp. switch (broke while re-installing) the one that screws into the back right of the head. Before I replaced the headgasket the temp. gauge never read above 95. I'm thinking perhaps that the sensor was already broken and only now I'm seeing the accurate temperature? Or is it normal for a engine that has been cold for around a week and a half to have the temp. run very high? Any help would be greatly appreciated! Thanks!

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Unread 11-07-2012, 09:44 PM   #2
jokerchief462
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I belive the actual operating temp should be at 210 degrees using a 195 degree thermostat? Thats what I read in the manual or are you reading in celcius I see from BC??? So quick conversion on the phone. So 90C is thermostat and 98.8C is the temp. Got it right now.

So when first started she heats up into the red yes happens all the time to mine after any work like that. Usually settles in right after a top off though maybe an air bubble happens a lot on these maybe needs a burp.

Have you tried to run it again? That was 120C which is 248 degrees fareneit.
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Unread 11-07-2012, 11:14 PM   #3
Nic
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I just ran it for about an hour on and off. No change in the overheating. I also burped the system and got out quite a bit of air. I think air might be getting into the cooling system but im not sure from where. Possibly from the new coolant sensor? It didnt go in very well. Thanks for the reply. Cheers
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Unread 11-08-2012, 06:19 AM   #4
Why J?
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You can check for continuity between the sensor plug and the block. If you have continuity than the sensor is bad. I just had a brand new out of the box temp sender be bad.

Also I have had a lot of luck in filling the system through the upper radiator hose. Do this by removing the upper hose at the rad and filling with coolant.
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Unread 11-08-2012, 09:52 PM   #5
Nic
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Checked the resistance at the sensor, was around 270 ohms when engine temp. was around 100-110, which I think is around the appropriate amount. Replaced the thermostat and that didnt change anything. I'm not sure if there is anyway air could still be trapped in the system, let it run on and off for a total of 2 hours now with the Rad cap off.. Perhaps I need to try it on an incline? Hopefully air isnt getting into the system from somewhere! Thank you for the suggestion! Cheers
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Unread 11-09-2012, 12:21 AM   #6
Nic
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Also when the temp. gauge read around 115 C (well above correct temperature) after running for a bit I removed the Rad cap and there was no hiss or anything. Could the cap be bad and not holding pressure?
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Unread 11-09-2012, 12:33 AM   #7
jokerchief462
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Yes replace it with a new one they are cheap.
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Unread 11-09-2012, 08:10 PM   #8
Nic
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Replaced the rad cap but it didnt change anything, still stuck in the same situation. I am getting alot of squealing from the belt, perhaps it has to be tightened?
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Unread 11-09-2012, 08:53 PM   #9
jokerchief462
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Is there any way one of the waterjackets got blocked off by chance. Something isn't right. When it heats up and the tstat opens you should see water flow in the rad. It should also build pressure with the cap; on something in the neihborhood of 14 psi. Is the thermostat opening. You can boil it on the stove and watch it work.
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Unread 11-09-2012, 09:33 PM   #10
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It took me a while to fully burp out all the trapped air, it usually gets caught in your upper most hose (don't know if that's where you were burping it from), when cool, squeeze the hose at the top there with the rad cap off and see if you get more bubbles out.

as jokerchief said, is the t-stat opening?
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Unread 11-10-2012, 11:25 PM   #11
Nic
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Just for fun I put in the old coolant sensor and found that it reads around 90-95, normal running temperature. While the new one I just got from NAPA is reading 115 or higher. Not sure which one to believe now. Before I repaired my Headgasket the old CTS never read as over heating so perhaps it is just somehow stuck on optimal running temperature. I've tried checking the resistance's across them but I find so many different charts on the internet I think im just gonna try another new one.

The Rad Cap is now retaining pressure now that I got a new one. And all the coolant passages should be fine, a few had alittle bit of junk in them but nothing to cause the temp to go straight up. If the new sensor does not work out I will try running the engine without the thermostat. If the engine heats up at the same speed I'll know its not the t-stat.
Thanks for the suggestions. Cheers!
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Unread 11-11-2012, 06:36 AM   #12
jokerchief462
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Any time you doubt the temp gauge many have gotten an infared gun to read the heat. Might be one of those fancy tools for the toolbox!! Glad to hear you are back to normal.
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Unread 11-11-2012, 09:44 AM   #13
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Running without a tstat will not let the engine get up to operating temp causing you to burn more fuel.Also when you start to drive around the coolant will flow to fast through the radiator and you will over heat.

Air in the system will cause alot of what you are talking about.If you are so worried about the system leaking ;get a pressure check done.This will show if you are losing pressure in the system and the cap.
Are you losing coolant ?is there white smoke when you run it?did you check/change the water pump?
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Unread 11-11-2012, 10:04 AM   #14
mike_breaker_5
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i think he is only going to run the jeep without the t-stat to eliminate the possibility that the overheating is being caused by the t-stat.

as far as running without a t-stat causing you to overheat i have personal experience that in the 4.0l ho, the 318 magnum, and any chevy small block (pre injection) this is not the case. in other engines it may happen but i know it will not happen with those engines with the rest of cooling system in proper working order. i have ran all of these engines without thermostats for prolonged periods and as stated i never even heated up to normal operating temps in any of the instances mentioned. you are absolutely correct that ,in an injected engine especially, cooler than operating temps will cause a loss in mpg's.

possibly in a vehicle that is under built in the cooling system i could see this happening, but with a clean rad and a good worrking and properly sized fan (electric or clutched), ihave not see this being the case.

i also will get on the air in the system band wagon. the first time i did a rad flush on the jeep after i originally bought it i had a terrible time getting all the air out. i had just the same issues you were describing. also as ejeeperguy said it could be an issue with your pump itself.
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Unread 11-11-2012, 11:59 AM   #15
Nic
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Is the any more effective method of getting air out of the system? I've tried running it with the rad cap off for a few hours now on an off. While doing this I was also squeezing the top rad hose, at first a few bubbles came out before but now there doesnt seem to be any. I also tried doing it on an incline which didnt improve anything. Any better methods?

As for testing the water pump I currently dont hear any grinding noises from the pulley. When I squeeze the top rad hose (with cap on) then let go there appears to be a bit of a surge in pressure, however not a very powerful one. I get a fairly healthy discount at NAPA so I think I may just go ahead and replace the water pump once I get the time. Maybe also the fan clutch? People always speak of hearing them "turn on" but mine sounds the same at all temperatures, I dont have much experience with these belt driven accessories. I think I might just have to empty every pocket on this one. Thanks for the help, Cheers!
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coolant , coolant flow , engine , head gasket , over heating

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