Coolant Level Dropping in Radiator

[explorer2030]

Recently I have found that the coolant level in my 3.6L Pentastar is always about 1/2"-3/4" low near the bottom of the radiator neck if I check it when the engine cools down after driving the vehicle. If I fill it back up until it touches the bottom of the radiator cap, the level goes back down to the same spot the next time I check it. It started doing this after I refilled the system the last time I serviced it, but I would be surprised if there is any residual air remaining because I used a vacuum filler followed up with a few cycles bleeding with a funnel.

I originally thought that there may be air getting pulled in from the end connections at the overflow tank hose during cooldown, but I found that the level also drops to this same spot immediately after pressure testing the cooling system with a cold engine. The coolant temps when running are stable between 203F-210F, and it has never overheated. I sprayed down all of the cooling sysem connections with soapy water, and used a borescope to inspect around the base of the oil cooler when I had it pressurized, but there is no evidence of any coolant leakage.

I am a bit puzzled because about an ounce of coolant will just seemingly disappear after each time I pressurize the system to 18 psi with the pressure tester. I can hear some gurgling as I release pressure from the tool, and the level will be near the bottom of the filler neck when I remove it (I noticed the level rise a little one time after letting it sit for a while after removing the tool). Is it possible there is an air pocket stuck deep in the system that gets compressed when I pressurize it making it seem like the level dropped at the radiator neck? I don't think it is leaking into a cylinder because the level drops this much even after a very short amount of time being pressurized < 2 minutes.. I see no evidence of coolant on the dipstick, and I was able to turn the engine over by hand after pressure testing it without hydrolocking.

 

[skyactiv]

Hopefully this will help: https://www.challengertalk.com/threads/3-6-oil-coolant-loss-with-no-signs-of-a-leak.677294/

 

[explorer2030]

Hopefully this will help: https://www.challengertalk.com/threads/3-6-oil-coolant-loss-with-no-signs-of-a-leak.677294/

Thanks for the reply. That article says the issue is the oil cooler assembly, but I just replaced that with a new Mopar unit about 12,000 miles ago and there is no leakage in the valley. I snaked a digital borescope in from the back and on both sides of the oil cooler from the front, and it's dry as a bone.

 

[Cujet]

I have to wonder if this is normal. Is the coolant simply moving to the expansion tank when hot and then not finding it's way back fully?

 

[explorer2030]

I have to wonder if this is normal. Is the coolant simply moving to the expansion tank when hot and then not finding it's way back fully?

I had the overflow tank hose removed and the nipple on the radiator neck plugged when I was pressurizing the system with the pressure tester, so I know the coolant wasn't escaping to the overflow tank. Prior to this issue starting a few weeks ago, the coolant level would always be touching the radiator cap anytime I removed it.

 

[MSCH]

instead of puzzling over the issue, why don't you wait and see how long it takes before the low coolant light comes on..

 

[explorer2030]

instead of puzzling over the issue, why don't you wait and see how long it takes before the low coolant light comes on..

Because I want to solve the issue before it gets to that point.

 

[MSCH]

Because I want to solve the issue before it gets to that point.

what if you don't have an issue.?
is that one ounce variation in coolant level causing any noticeable problems?
Do you know for sure you are losing coolant or are you trying to fix something that isn't broke?
I'll leave it at that.

 

[explorer2030]

what if you don't have an issue.?
is that one ounce variation in coolant level causing any noticeable problems?
Do you know for sure you are losing coolant or are you trying to fix something that isn't broke?
I'll leave it at that.

Yes I know its an issue because I monitor the coolant closely and it never dropped like this before in the radiator. Something occurred after my last servicing to cause this, and I want to get to the bottom of it. I pulled a deeper vacuum 29.25" on the system with a modified Airlift vacuum filler last time to try to eliminate the need for additional funnel bleeding, and it makes me wonder if it's possible that one of the tubes in the radiator or the head gasket could have been affected enough by this stronger vacuum to cause a leak. I used an AC vacuum pump connected to the main body of the Airlift with a charging hose rather than the venturi vacuum generator that came with the tool because it's only capable of at best 28" vacuum and it leaves a fair amount of air behind.

The only other thing that occurred during this servicing that seems related was that I pressurized the cylinders with a leakdown tester, and I turned my air compressor regulator up to 115psi on one cylinder because the pressure on the tool's gauge would only go up to 70psi even with the knob turned all the way clockwise when the air compressor's regulator was set to around 90psi. I was trying to get to 80psi on the tool, but I stopped at 115psi on the air compressor without getting the gauge on the tool to go up to 80 psi. It's possible the gauges got stuck on the tool, and I could have pressurized one cylinder to 115psi.

 

[MSCH]

29 inches of vaccum is only about 14 psi of negative pressure. since coolant pressue in a running engine is higher than that I doubt that little vacuum pump posed a problem.

I suggest you re think what you are doing and wait and see what is really going on.
It has been my experience that if a person waits, if there is truly a problem it will be readily apparent.

 

[racer12306]

We put a head gasket on our 3.6 pentastar last year, about 80-85,000 miles on the vehicle.

It would lose just a little coolant over time. That was the only symptom.

Pretty sure the shop pressurized the system, maybe overnight, and then looked in the spark plug holes to confirm coolant entering the cylinder.

Obviously this is one of the worst case scenarios, but just my experience.

 

[benjamming]

Does UOA show any elevated levels of coolant?

 

[explorer2030]

Does UOA show any elevated levels of coolant?

I haven't got to that point yet, but I did check the dipstick after running the engine and there is no evidence of coolant on it. If the pressure tester pushed a few ounces of coolant into one of the cylinder's, I would think this would work its way past the rings to the sump and be visible on the dipstick.

 

[Lubener]

For strange hard to find leaks, I always start looking at the weep hole on the water pump. I am not familiar with a 3.6. Hopefully the pump is externally mounted.

 

[explorer2030]

For strange hard to find leaks, I always start looking at the weep hole on the water pump. I am not familiar with a 3.6. Hopefully the pump is externally mounted.

The pump is externally mounted, but I can't see the weep hole because I think it's behind the serpentine belt pulley. I was underneath the vehicle and didn't see any evidence of coolant residue on the housing below this area though.

 

[Lubener]

The pump is externally mounted, but I can't see the weep hole because I think it's behind the serpentine belt pulley. I was underneath the vehicle and didn't see any evidence of coolant residue on the housing below this area though.

Use a small telescoping mirror to see if any staining exists near the hole.

 

[k1xv]

It has always been my experience, when coolant is disappearing without leaking on the ground, that it is going into the engine cylinders or the crankcase. I lean toward the cylinder head gasket theory.

 

[Bladecutter]

We put a head gasket on our 3.6 pentastar last year, about 80-85,000 miles on the vehicle.

It would lose just a little coolant over time. That was the only symptom.

Pretty sure the shop pressurized the system, maybe overnight, and then looked in the spark plug holes to confirm coolant entering the cylinder.

Obviously this is one of the worst case scenarios, but just my experience.

It has always been my experience, when coolant is disappearing without leaking on the ground, that it is going into the engine cylinders or the crankcase. I lean toward the cylinder head gasket theory.

Yup.
Warm up engine, shut engine off.
Pull spark plugs.
Pressurize the cooling system.
Insert borescope into all cylinders until you find the one that has weepage between cylinder head and cylinder bore.
Repair motor.

 

[explorer2030]

It has always been my experience, when coolant is disappearing without leaking on the ground, that it is going into the engine cylinders or the crankcase. I lean toward the cylinder head gasket theory.

Whats odd though is that I will lose the approximate 1 ounce of coolant in around 2 minutes of pressurizing the cooling system with a Stant 12270 pressure tester used on a cold engine. I would think it would take a significant head gasket leak to push that much coolant into a cylinder in that short of a time period, but maybe it's possible.

After redoing the pressure test 3-4 times refilling the system each time, I wondered if there would be enough coolant in the cylinder to hydrolock the engine. I was able to turn it over by hand without issue and it started up fine afterwards. I get no overheating when driving the vehicle, and coolant temps stay within normal range 203-210F.

 

[TheOilWizard]

Have you checked the radiator closely for leaks?