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Hemi 5.7 overheating after new thermostat and air purge. #2853154
11/29/20 10:48 PM
11/29/20 10:48 PM
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Ok. Changed the thermostat and began sudden over heating that l didnt have before. So the video l found suspected air trapped. I got an Allen wrench and ratchet and pulled the purge plug above the thermostat and had some air, so l was excited that l resolved the issue. But on test run, the thermostat stayed middle like it should look, but the engine got HOT AND steamed and smoked from below the Coolant well. What is Going on?!?!?!?!.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853188
11/30/20 12:33 AM
11/30/20 12:33 AM
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Bad thermostat maybe. Take it back out and put it in boiling water to se if it opens.You do have it installed like the picture right. What was the reason to swap the thermo to begin with?

thermo.jpg
Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: stumpy] #2853191
11/30/20 12:45 AM
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This is the second try at the thermostat. Returned one in case that was what's wrong.
I put it in exactly as the first one came out.
The thermostat sometimes Reads right. And jumps up hot, then after an air purge and refill of fluids it will get got but stop at middle of the dial for temp. Like it's perfect temp but not.
I can pull it in the morning and check its positioning again. I have no prob checking that.
It appears to be right but lm no professional. I 'believe " I have put it in correctly. I can be wrong.
Rather be wrong and learn. Just wanna figure this out.
The thermostat Does work half the time. The other half of the time it acts like its perfect but l am boiling anyhow. Like it reading half the temp. Can you really get 2 bad thermometers in a row. Lol

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853192
11/30/20 12:46 AM
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I will boil it in the morning and look

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853194
11/30/20 12:49 AM
11/30/20 12:49 AM
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You say the temp gauge reads correctly in the middle. Where is the water you saw? What are you referring to when you say coolant well? Engine should be running at about 210*. What year and model is the vehicle?

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: stumpy] #2853226
11/30/20 07:59 AM
11/30/20 07:59 AM
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This is a very common problem on all 5.7 and 6.4 ( thermostat failure). When you drain the cooling system on these you have to be patient and bleed the system several times. It will take a while but its not a huge deal. I am curious about something though- I've changed thermostats on 2 separate 5.7 and a 6.4 and never had to bleed the system. I saw a clever backwoods way to do it. Just crack the housing off on the corner and hold a plastic ziplock bag under to collect coolant. When it stops running out ( yes, you have to clamp rad hose)
you can throw the new stat in, refill and be on your way.

Does it make a rushing water noise on start up ( noise from behind dash)?

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: moparjim79] #2853228
11/30/20 08:14 AM
11/30/20 08:14 AM
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moparjim79 so just loosen or remove the bolt, or do you actually separate the parts at the gasket surface? Thanks

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: moparjim79] #2853273
11/30/20 11:22 AM
11/30/20 11:22 AM
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Originally Posted by moparjim79
This is a very common problem on all 5.7 and 6.4 ( thermostat failure). When you drain the cooling system on these you have to be patient and bleed the system several times. It will take a while but its not a huge deal. I am curious about something though- I've changed thermostats on 2 separate 5.7 and a 6.4 and never had to bleed the system. I saw a clever backwoods way to do it. Just crack the housing off on the corner and hold a plastic ziplock bag under to collect coolant. When it stops running out ( yes, you have to clamp rad hose)
you can throw the new stat in, refill and be on your way.

Does it make a rushing water noise on start up ( noise from behind dash)?



DId same thing on my Magnum with 5.7 . . . just took the bolts off, got the housing loose and let coolant drain into ziplock bag . . . pulled old stat, put in new stat (making sure gasket around stat is in place correctly), put on housing, bolted up, and added the coolant from ziplock bag to overflow . . no issue.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: stumpy] #2853286
11/30/20 11:57 AM
11/30/20 11:57 AM
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Do you see the recessed Allen behind the thermostat housing?

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853416
11/30/20 03:48 PM
11/30/20 03:48 PM
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Originally Posted by KcCrown
Ok. Changed the thermostat and began sudden over heating that l didnt have before. So the video l found suspected air trapped. I got an Allen wrench and ratchet and pulled the purge plug above the thermostat and had some air, so l was excited that l resolved the issue. But on test run, the thermostat stayed middle like it should look, but the engine got HOT AND steamed and smoked from below the Coolant well. What is Going on?!?!?!?!.


If I understand what you've posted correctly it doesn't sound like the thermostat is the problem.

You don't specify what kind of vehicle it's in.

You say that the temperature gauge is staying in the normal range.

Guessing that it's a car (Charger, Magnum, 300).

Is there damage (crack, hole) in the coolant reservoir anywhere?
There are two chambers in the reservoir, one pressurized and one is the overflow bottle.

The pressurized is obviously where the radiator cap is.
If there's a hole or crack in it the cooling system won't build pressure.

The side closest to the outer fender is the overflow area.
If it looks full cooling system pressure has filled it, it shouldn't be full.

You need to know exactly where the coolant is coming out from.

You also need to check the system with a coolant pressure tester.

It will help diagnose where coolant is coming out at.
You can probably rent one from an auto parts store (usually rental is free with a deposit).


Kayse can't keep up at all now. lol
Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: a12rag] #2853489
11/30/20 06:18 PM
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I replaced thermostat and things are fine for 2 to 3 weeks.. then, suddenly overheat.
I suspect l have air locked in system. I finally got Allen wrench to break the bleeder open and thought it was fixed, then over heated. I will bleed again now and continue to try to resolve this. From everyones info it very likely is a air pocket l have to get all the way out.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: a12rag] #2853494
11/30/20 06:30 PM
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My cousin who knows a lot more than l basically did this . He cracked the housing and bled it off this way and it worked a while. He did it several times and it lasted a mnth. So basically it seems somehow after a mnth of running l pull air somehow and have to deal with this again. Is my fluid getting too low and then sucking air? Not sure . For now l am gonna pull the bleed bolt again and do it several times and see if l can get all the air out. This MUST be what's wrong from everything l have read. When l change the thermostat out it seems to resolve for a while. But not always. Now lm using the bleeder bolt and seeing if this is a better location at higher level above the thermostat level to get it all out. Fingers crossed.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: a12rag] #2853498
11/30/20 06:33 PM
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This basic method seems to work for 3 to 5 weeks then sudden issue. Like somehow l pull air into the system over time or suddenly after several seeks. Is the fluid getting low and allowing air in. ? Do l need to keep my eye on the fluid level constantly.?
My 5.7 has a bleeder bolt right above the thermostat housing. I am TRYING TO bleed it out from that. This is 3rd attempt. It seem to be taking many times bleeding. But that sounds normal maybe

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853503
11/30/20 06:48 PM
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If you are not loosing coolant and it stays full you might have head gaskets or cracked head. You can get a test kit that will show if there is combustion gasses in the coolant.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853505
11/30/20 06:54 PM
11/30/20 06:54 PM
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On my 06 Magnum, I followed the service manual instructions. You open the bleeder, fill the reservoir and let the coolant drain into the car until it comes out of the bleeder. I did this over a year ago when I changed my water pump and thermostat. Never had any issues. It took all afternoon, but it worked.


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Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: NITROUSN] #2853537
11/30/20 08:15 PM
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Coolant drops into system normal and has to be refilled. No fluid in oil whatsoever. 1

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: GTSDart340] #2853538
11/30/20 08:17 PM
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This what l am doing. However. I open the bleeder and it flows out the bleeder and l fill it. I start the car and right away steam from under the engine.. gauge doesnt even rise much before the engine and fluid are obviously hot. I shut it down. Am waiting to cool down to pull the bleeder again. So far all 3 times lve done this, l have air again to bleed. Not sure [censored].

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: SNK-EYZ] #2853539
11/30/20 08:23 PM
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No leaks are apparent. Fluid stays full and pressurized.
Fluid only drops after the engine warms and the thermostat opens. Then it drops. Steam does roll up from the bottom if the engine once it's hot. Not sure why. But it doesnt seem to be a leak? It doesnt drop in level or pressure. It is under pressure. It seems like l might have air trapped and it may be taking several times to bleed it all out.
I dont get it.
This is its second thermostat. It acts fine for weeks after the thermostat is installed. Then 5 weeks after it suddenly over heats and acts like it has pulled air into it somehow. Then the air is trapped.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: GTSDart340] #2853540
11/30/20 08:25 PM
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So. Curiosity. What part took all afternoon. Did you have to open the bleeder several times like l am doing.

Re: Hemi 5.7 overheating after new thermostat and air purge. [Re: KcCrown] #2853541
11/30/20 08:25 PM
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Originally Posted by KcCrown
This what l am doing. However. I open the bleeder and it flows out the bleeder and l fill it. I start the car and right away steam from under the engine.. gauge doesnt even rise much before the engine and fluid are obviously hot. I shut it down. Am waiting to cool down to pull the bleeder again. So far all 3 times lve done this, l have air again to bleed. Not sure [censored].


Ok, KC, we are trying to help you, dont get frustrated. You have a breach in your cooling system. As stated above, at this point , get a pressure tester( buy or rent) pressurize it cold and if you have to, walk away from it for a while. Some pressure tests reveal the issue immediately, sometimes its a slow seep. I thought at first maybe you had a bad rad, but then you talk about steam from under the engine. This is the tricky part of online diagnostic steps. What one person sees as a problem someone more familiar with cars may see a slew of different issues all related/causing the "issue". Hang in there well get it. Go get your pressure tester boy!

Last edited by moparjim79; 11/30/20 08:27 PM.
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