Coolant Loss - JeepForum.com
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post #1 of 31 Old 01-15-2020, 09:58 AM Thread Starter
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Coolant Loss

Sorry this is going to be long:
I bought a 2004 WJ 4.7 that was not running, pulled the engine to find the typical dropped seat problem.

I rebuilt the engine including new seals, pistons, head gaskets, re-manufactured cylinder head assemblies (complete with cams), timing chains & sprockets, bearings, etc.

Reinstalled the engine and it started right up, good oil pressure, good coolant temperature control (rising until thermostat opening and then stabilizing).

I have put about 300 miles on the rebuild and find that I am loosing coolant but not seeing any external evidence of a leak.

I did a pressure test and have a slow loss of pressure (although I am not sure the tester was sealing very well). The pressure loss appears about the same starting cold, or running with the cap loose until the thermostat opens and then stopping the engine to test.

Not a cloud of white smoke in the exhaust and this time of year it is hard to tell if the white smoke seen when cold is typical or not.

I drained a small amount of oil after it sat overnight and didn't see any obvious signs of coolant.

The cylinder heads came from a source that claims that they check for cracks in the re-manufacturing process. It could still be a cracked head but not sure how to tell which one, or where to look.

Any insight about where to look and potential sources of coolant leak under pressure would be appreciated.


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post #2 of 31 Old 01-15-2020, 10:06 AM
paulvon
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I had a similar issue.

The leak only happened when the engine is hot. It also was very slight.

In the end I used a bottle of K-seal and the problem was solved. The good thing with K-seal is that it does not clog up the heater core.

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post #3 of 31 Old 01-15-2020, 10:03 PM
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Sounds like you need a cooling system pressure tester. Most auto parts stores have these for rent/loan. If you have an external leak, it should show up under pressure with the engine off. If no external leak is found, then its time to look deeper for an Internal leak. Surefire way to diagnose internal coolant leaks is to do a combustion test at the open radiator neck. most auto parts stores have the testers for sale. It consists of a graduated glass cylinder with a rubber neck on the bottom, and a vial of special fluid to put in the tester. Use the tester at the open Radiator neck while the engine is idling. Dont forget to remove a small amount of coolant from the radiator first. I forget which color is good and which is bad, but if the heads/headgaskets are leaking the fluid in the glass cylinder will change color. If you have just done all that work to the engine, i would not recommend using the K-seal. I wouldnt want that stuff in my near new engine. Good Luck

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post #4 of 31 Old 01-16-2020, 08:13 AM Thread Starter
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Thanks for the responses.

Like Bigrigr I am not inclined to try K-seal on a new rebuild although I must admit I am not anxious to pull the engine apart again.

The initial pressure test I did was with a tester I borrowed from a local auto parts store but I seemed to have a problem getting the tester to seal to the radiator fill neck. I would like to suspect the tester rather than the engine for the slow pressure drop but given the coolant loss that is probably wishful thinking.

I will look into the combustion test but if there are any other suggestions they would be greatly appreciated.

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post #5 of 31 Old 01-17-2020, 09:48 AM Thread Starter
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I borrowed a combustion detector from O'Reilly and it didn't indicate any combustion leakage into the coolant after several minutes. I am hoping that it is correct and that means I don't have a head gasket problem, or a cracked head.

However, that doesn't help resolve the coolant loss question.

I can believe the initial pressure test results that showed a slow pressure loss were flawed given the problems I had with the tester sealing on the radiator but I am still convinced that I am loosing coolant somewhere.

My plan of attack from here is to continue to run it and monitor the coolant loss and any indication that there is coolant in the oil, or exhaust and hope the leak path is external and will eventually reveal itself.

Any other suggestions would be appreciated.

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post #6 of 31 Old 01-17-2020, 12:23 PM
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The results of the Combustion test is good news. I vote there has to be a slightly loose hose clamp somewhere. I would go back over every clamp and hose you can and just double check. Its possible you have a slight leak that might be near the exhaust(like a heater hose) that leaks onto the hot exhaust and evaporates before it drips on the ground. If you still cant find anything obvious, double check the A/C drain for signs of coolant leaking(slight leak in heater core?). At least you arent tearing into the motor. Im sure you already know, but just dont let the coolant level get low enough to get air into the system. We all know how hard that is to get back out, and it can cause hot spots inside your engine that the guage never knows about. Thus causing engine damage to your new engine. Good luck

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post #7 of 31 Old 01-17-2020, 12:26 PM
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Another thought just popped up, did you replace the water pump when you did the overhaul? Most people do, but if not, could it be leaking out the weep hole slightly? Look for the telltale trail?

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post #8 of 31 Old 01-17-2020, 03:22 PM Thread Starter
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I didn't replace the water pump in part because it appeared to have been recently replaced by the PO.

Another bit of information. I drove to and from town (about 5 miles each way) with a few hours stopped in town. Upon return home I pulled into the garage and proceeded to replace the rear wiper blade, which took a few minutes. While I was doing the wiper blade replacement there was a sudden and relatively significant amount of white smoke out of the tailpipe (engine is not running and hasn't been for 2-3 minutes). I am speculating that there is a crack is one of the cylinder heads that opens up under heat and coolant system pressure from a coolant passage to an exhaust port.

If that is the case I am looking at replacing one of my newly reconditioned heads, but how to decide which one and then prove to the supplier that the head should be replaced under warranty is a problem. Changing heads without pulling the engine again may be possible but I am not sure its worth the pain given that so much of the engine needs to be disassembled to change a head its not much more work to pull the engine and be able to work on it in the open.

This is not the outcome I was hoping for and certainly not what I expected when I rebuilt the engine.

Any thoughts on diagnostics would be appreciated.

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post #9 of 31 Old 01-18-2020, 01:56 PM
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+1 on checking the heater core.....
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post #10 of 31 Old 01-21-2020, 02:59 PM
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Have you checked the transmission fluid? If I recall correctly, the tranny cooler is in the radiator.
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post #11 of 31 Old 01-22-2020, 09:43 AM Thread Starter
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I have not checked the transmission fluid but that is a good thought.

I am still confused/concerned about the puff of white smoke from the exhaust several minutes after the engine was shut off and my guess that it was coolant leaking into the exhaust system under hot soak conditions ignited by the catalyst. If that was the case I am not sure how to determine which head was the source.

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post #12 of 31 Old 01-22-2020, 12:20 PM
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I assume the freeze plugs are all new and tight, including those at the rear of the engine?
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post #13 of 31 Old 01-22-2020, 02:06 PM
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I read a post in another thread by a fellow forum member(I looked quickly, but didnt run across it again) that said he pulled the spark plugs and dabbed a piece of paper towel on the tops of the pistons after it had sat all night. Usually bad head gaskets/cracked heads start out leaking a small amount into the cylinders as the engine cools down. The coolant remains pressurized until the coolant temp lowers, so with the engine off, there are no combustion pressures keeping the coolant from entering the cylinder, so the coolant can sneak by the crack/leak and pool ontop of the piston until you try to start it the next morning. It would kinda be a pain to remove all 8, but it might help narrow things down if you find one thats wet?

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post #14 of 31 Old 01-23-2020, 07:24 AM Thread Starter
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Thanks, I will consider that as pulling spark plugs is easier than pulling exhaust manifolds. I would probably need to rotate the engine with the paper towel in each cylinder to get each piston to the top of the stroke where the pooled coolant could contact the paper towel.

I didn't replace the freeze plugs but they do not show any signs of coolant loss, although I will recheck.

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post #15 of 31 Old 01-24-2020, 12:09 AM
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Let us know what happens. I pray you dont have any wet pistons, it always sucks to go back into a fresh motor. Good luck

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