Jeep Wrangler Coolant Disappearing

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Jan 6, 2021
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Hello,
I have browsed these forums here for the past couple of weeks and was wondering if you all have some answers for me. I have recently bought a 2018 JK Wrangler back in October with around 4600 miles on it. I do not remember the initial coolant level on the vehicle however remember it was within normal limits. Fast forward a few months in November or so and I noticed that when the engine was completely cold overnight the coolant level in the overflow bottle was just below the minimum line. I bought MOPAR OAT antifreeze and filled the overflow bottle to an inch above the minimum line when the engine was completely cold. This level held steady for a month or so. Fast forward to the past 2 weeks and I took about a 300 mile trip down to North Carolina (I live in Virginia) and noticed the coolant level dropped about a 1/4-1/2 of an inch (however it was somewhat warmer down there). When I returned home I let the vehicle sit and drove my other car, and upon checking my coolant today it was back sitting on the minimum line. Oil is non milky in appearance and no coolant smells. Is this downward fluctuation normal for vehicles due to the temperature being colder at night? The vehicle is under warranty still so I can bring it in to the dealer if necessary. Many thanks!
 

AutoMechanic

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Welcome fellow Virginia resident lol. If it is still under warranty I’d totally take it in to see if they can find anything. I’m glad none has appeared to be in the oil that’s never good. Maybe you have a slow leak somewhere. So it’s not showing up on anything or the ground right?
 
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Hi @Gonefar32 Yes the fluid will go up a down a bit. Be sure to check it after a lot sit (say overnight) and take note of the ambient temp. If roughly the same it should line up fairly well but its not impossible to have a bubble in the line (if your stomping on it) which can get trapped and change the level a bit. If it's working its way up and down 1/4 -3/8 of an inch I wouldn't think twice. If it is slowly dropping consistently and you must add coolant sometimes the water pump seals are damaged. They actually work by consuming coolant to keep them lubricated and cool but if damaged they can actually burn up a lot more than you think. Look under the pump and behind the pulley (if you can). You'll see a small hole under the water pump housing. That hole allows the "bearing overflow" to drip out under certain conditions but it's usually only a drop or two. If you see a weep or the area is wet you might have a bad bearing.

Hope this helps!
 
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Also! Make sure you use Chrysler coolant. I believe it is HOAT (Hybrid organic acid technology) vs. OAT or pure IAT coolant but the three are not friends and it's best to keep the coolant class the same. You probably already knew that but coolant is not just coolant anymore... boo
 
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You can drain a sample of oil and send it to Blackstone Labs or another oil analysis lab. They can determine if there is coolant in the oil. For $25 it might be cheap insurance.
 

Gonefar32

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Jan 6, 2021
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You guys really totally awesome! I scheduled to bring it in to the dealer for them to see if there is an issue
 

Gonefar32

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Jan 6, 2021
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The Wrangler cooling system is not completely sealed, the overflow bottle has a vent. Some evaporation is normal. Add water to top off instead of coolant.
Just out of curiosity what is your reasoning behind adding water instead of mixing coolant? And I saw the overflow has a tube that allows overflow above the max to basically dump onto the ground...is this what you are referring to?
 

Gonefar32

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Jan 6, 2021
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Hi @Gonefar32 Yes the fluid will go up a down a bit. Be sure to check it after a lot sit (say overnight) and take note of the ambient temp. If roughly the same it should line up fairly well but its not impossible to have a bubble in the line (if your stomping on it) which can get trapped and change the level a bit. If it's working its way up and down 1/4 -3/8 of an inch I wouldn't think twice. If it is slowly dropping consistently and you must add coolant sometimes the water pump seals are damaged. They actually work by consuming coolant to keep them lubricated and cool but if damaged they can actually burn up a lot more than you think. Look under the pump and behind the pulley (if you can). You'll see a small hole under the water pump housing. That hole allows the "bearing overflow" to drip out under certain conditions but it's usually only a drop or two. If you see a weep or the area is wet you might have a bad bearing.

Hope this helps!
It is very helpful information. I am definitely having a hard time gauging if it is actually slowly decreasing or just due to it getting colder and colder outside at night. I know you aren’t supposed to open The radiator cap when the engine is hot, however if you open it even when it is cold is it possible to introduce air into the system?
 
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It is very helpful information. I am definitely having a hard time gauging if it is actually slowly decreasing or just due to it getting colder and colder outside at night. I know you aren’t supposed to open The radiator cap when the engine is hot, however if you open it even when it is cold is it possible to introduce air into the system?
Not if it's full. And if it's not full then you already have air in it.
 
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Just out of curiosity what is your reasoning behind adding water instead of mixing coolant? And I saw the overflow has a tube that allows overflow above the max to basically dump onto the ground...is this what you are referring to?

Well admittedly I am assuming the water evaporates but not the coolant. If that is incorrect (someone here will jump on that I am sure) then disregard.
 
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Another thing you can do is to borrow a pressure tester from Advance Auto or Autozone or whatever parts store is near you. Pressurize the system to 15PSI and leave it overnight.

If there is an external leak it will be VERY obvious the next morning.
 

Gonefar32

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Jan 6, 2021
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Hey guys! Little update. Brought it to the dealer and the radiator had a small leak. They are replacing it under warranty!
 
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If you have the 3.6 Pentastar it is probably leaking at the oil cooler in the middle of the engine valley. Very common. Look down around the oil filter housing for coolant laying there pooling up.

EDIT - just saw it was diagnosed as the radiator
 
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