2008 JK coolant reservoir bubbling

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james6873

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***2008 wranlger*** I had a couple times where after driving for about 25 minutes, sitting at a traffic light it would seem to boil over- as in the reservoir was bubbling rapidly even after i turned the vehicle off. I got stationed in japan for a while and now im back to NY where i had my jeep shipped and im having this same problem once agin. The coolant bubbles after about 25 minutes of driving it, and continues bubbling in the reservoir until the engine cools a little. I've super flushed the entire system, replaced the thermostat& gasket, replaced the coolant, bled the air, inspected hoses for leaks and clamps as well. It's not a head gasket because i've been driving it for way too long without exploding, also no coolant in my oil and no steam out my exhaust/under the hood. Could it be a crack in my radiator or water pump/gasket creating air bubbles every time i drive it?

side note- the other day i found i havent been using the right coolant (i thought coolant was universal) (ive been using peak 50/50). i heard this can cause corrosion/air leaks in your water pump. Also the jeep is a manual, idk if that makes a difference.
 
If you had a crack in the radiator or water pump you would have antifreeze all over the engine compartment.

Is your cooling fan working? You can't mix different types of coolant but you can change the coolant and put a different type in.
 
BLACKJKU said:
If you had a crack in the radiator or water pump you would have antifreeze all over the engine compartment.

Is your cooling fan working? You can't mix different types of coolant but you can change the coolant and put a different type in.
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REPLY:
my cooling fan works, yes. the temperature sensor isn't corroded or anything. and the temp gauge reads a neutral temp even when the bubbling is happening. I also read that a small crack in a gasket on the water pump can allow air into the system.
EDIT: i thought you could only use OAT coolant on jk's
 
if you add to your existing Factory coolant you have to use the same as what's in there but if you drain and flush you can use whatever you want. You just can't mix certain ones together.

Have you replaced your radiator cap?
 
BLACKJKU said:
if you add to your existing Factory coolant you have to use the same as what's in there but if you drain and flush you can use whatever you want. You just can't mix certain ones together.

Have you replaced your radiator cap?
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REPLY: I haven't replaced my rad cap. But it doesn't seem to be loose or anything. it also has 100k miles and youre supposed to change the water pump after 100k
 
I've never heard of replacing a water pump at certain miles, just when they leak water out the weep hole and the bearing is bad.
 
BLACKJKU said:
I've never heard of replacing a water pump at certain miles, just when they leak water out the weep hole and the bearing is bad.
Click to expand...


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Check out #2 on the list, it sounds like this is my case
 
A radiator that the cooling tubes are dirty on the outside and also corroded on the inside will cause issues.
 
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james6873 said:
REPLY:
my cooling fan works, yes. the temperature sensor isn't corroded or anything. and the temp gauge reads a neutral temp even when the bubbling is happening. I also read that a small crack in a gasket on the water pump can allow air into the system.
EDIT: i thought you could only use OAT coolant on jk's
Click to expand...
No, absolutely no. I just went through this with our 2008 Jeep JK. Boiling, you name it.

1. Up to 2012, Chrysler had manufacturer recommended HOAT for the JK. 2013 and newer OAT.
2. If you mix at all, there can be a chemical reaction that causes a gel effect, no bueno.
3. OAT alone in the older JKs, have caused boiling issues, total PITA on this whole "which coolant" thing in my opinion, but it matters.
4. I would replace the cap no matter what, even if it doesn't look like an issue.


Here's what I walked through on my 2008:

I did a non take apart flush if you will. I emptied the radiator. I filled the open space in radiator with distilled water.

Ran for 5 minutes, shut off and drained radiator, and put in distilled water. I repeated that until it was as clear as my patience would let me get it. (By the way, if the coolant coming out isn't orange, then someone put OAT in, not good). You may need to do a more intense flush to get it all out.

I then emptied the radiator and put filled with (non 50/50) so full strength HOAT ( pain in the rear to find, actually did at Autozone, O'Reilly or Advanced had no HOAT at all). So distilled water is in the engine etc, radiator emptied, and filled it with 100% orange HOAT. I did this on a hill so that the back of the engine didn't have bubbles.

I also pulled out the overflow and emptied it, then put 1" marks with a sharpee from the low mark to full mark to see easily for my testing, then I put it back and filled it to full.

From cold, I started the Jeep and let it idle. I had an OBDII bluetooth like the ones Chris has recommended on this forum from Amazon, with JSCAN software on my iphone. That way I saw the EXACT temperature the sensor was sending to the engine.

I kept checking the top hose and at the correct temp, it got hot when the thermostat opened, so that was fine.
I then watched, and there is an exact sequence when that stupid fan will come on, turn off, etc. I'll need to look, someone did a great write up where I saw all this, and mine followed that. The overflow level will change as it heats etc.

Just eliminating issues, thermostat and fan, and the sensor, if there is a crack letting air in, then it's letting coolant out, you would see it.
 
Chris said:
How many miles are on the thing? What does the coolant look like visually?
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REPLY: 106k miles... The coolant is and was green, ("peak" brand 50/50). like i said i did a full flush- heater core, engine block, radiator and everything and the water ran clear through it after the coolant was out. The coolant that I flushed was sitting for about 2 years with a start every weekish because i was stationed overseas. I Don't think the coolant even leaks to be honest, just somehow air is getting into my system every time i drive it.
 
Chris said:
How many miles are on the thing? What does the coolant look like visually?
Click to expand...
REPLY: 106k miles... The coolant is and was green, ("peak" brand 50/50). like i said i did a full flush- heater core, engine block, radiator and everything and the water ran clear through it after the coolant was out. The coolant that I flushed was sitting for about 2 years with a start every weekish because i was stationed overseas. I Don't think the coolant even leaks to be honest, just somehow air is getting into my system every time i drive it.
 
james6873 said:
REPLY: 106k miles... The coolant is and was green, ("peak" brand 50/50). like i said i did a full flush- heater core, engine block, radiator and everything and the water ran clear through it after the coolant was out. The coolant that I flushed was sitting for about 2 years with a start every weekish because i was stationed overseas. I Don't think the coolant even leaks to be honest, just somehow air is getting into my system every time i drive it.
Click to expand...

Air can only get into it from a combustion chamber. You can get the coolant tested for combustion gasses.
 
Last edited:
cpwolf said:

This write up pdf helped me with some of the very specifics, when fan comes on, coolant level, just specifics that helped me figure out my issues.

Cap had a tiny leak that caused issues and that was main problem, but the overflow also had a small crack and when hot would leak out.
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REPLY:
Holy crap you might have given me the answer here. just a bad ECT sensor then, (and possibly radiator cap) I'll get both replaced and let you know how it goes.
 
BLACKJKU said:
Air can only get into it from a combustion chamber. You can get the coolant tested for combustion gasses.
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REPLY: im not saying you're wrong, but this is what i've read. Also, maybe a bad ECT sensor is making the coolant steam building pockets of gas instead of liquid.. (thank you cpwolf)

Screen Shot 2020-09-02 at 8.55.34 PM.png
 
Well, it’s an easier start, I seriously hope that is it vs something else. HOAT is orange, I’d make sure that’s what you put in as well.
 
****!!!!FIXED!!!!**** basically what I assume was happening is that
james6873 said:
***2008 wranlger*** I had a couple times where after driving for about 25 minutes, sitting at a traffic light it would seem to boil over- as in the reservoir was bubbling rapidly even after i turned the vehicle off. I got stationed in japan for a while and now im back to NY where i had my jeep shipped and im having this same problem once agin. The coolant bubbles after about 25 minutes of driving it, and continues bubbling in the reservoir until the engine cools a little. I've super flushed the entire system, replaced the thermostat& gasket, replaced the coolant, bled the air, inspected hoses for leaks and clamps as well. It's not a head gasket because i've been driving it for way too long without exploding, also no coolant in my oil and no steam out my exhaust/under the hood. Could it be a crack in my radiator or water pump/gasket creating air bubbles every time i drive it?

side note- the other day i found i havent been using the right coolant (i thought coolant was universal) (ive been using peak 50/50). i heard this can cause corrosion/air leaks in your water pump. Also the jeep is a manual, idk if that makes a difference.
Click to expand...


*******!!!!!!!FINALLY FIXED!!!!!!!*******

REPLACED ECT SENSOR. Basically what i assume was happening was the engine coolant temperature sensor was reading about 30-40 degrees lower than it should- not completely broken just a little off. (which is why it wouldn't show on OBDII). This was allowing the coolant to reach its boiling point before the fan kicked on which made it seem like there was air entering the system, but it was just the coolant boiling and creating pockets of coolant vapor. (all while my temp gauge was reading normal). I replaced the ECT sensor and the fan now turns on while idling/slow traffic. I didn't even realize the fan wasn't turning on because at highway speeds (35mph+) the fan doesn't need to kick on and it wouldn't boil over. Thats why it seemed to "randomly" happen. Thank you so much to cpwolf for the PDF and the solution.
 
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Can't always be right sometimes it's just a guessing game when your trying to fix a vehicle over the internet. BUT in post no 2 I did ask if your cooling fan was working , guess I should have asked if the sensor was reading right to turn the fan on when it's supposed to. It looks like it was a pretty cheap fix anyway after all.

Thanks for updating us and letting us know the fix.
 
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