Coolant consumption mystery, looking for more "aha!" instances

[1stofmanyjeeps]

Hello everyone, I have a 2001 Jeep Wrangler 4.0 w/ 108k miles that is consuming a lot of coolant. It doesn't appear to be entering the combustion chamber as the engine has great compression (165-170psi in all cylinders) and the spark plugs appear as expected, no white residue. It doesn't appear to be leaking from any usual suspects. I have UV dye in the coolant and have pressurized the system. During my ownership, 65k-present, the Jeep has never overheated and appears to be in proper working order, aside from the coolant consumption. The issue started in early September of 2023 when I observed a leaking water pump. Since then, I have replaced the water pump, radiator, and a lower radiator hose, but still the consumption persists. I'm on the cusp of bringing it into a shop, but I'd love to get some opinions on other things to investigate.

As a potential clue, as baffling as this sounds, I appear to have UV dye on the leading edge and bottom of my passenger rear drum, but it exists there in isolation, I don't see any signs of where the dye could have originated and it doesn't appear to be on any other nearby surfaces, for cross-reference, the dye isn't present on the driver's side drum.

Thx!

History:
9/7/23 94,894 gurgling sound after turning off engine, coolant tank completely empty, air gap on top of radiator, added 1400cc to be at coolant tank full, added 400cc to top of radiator
9/15/23 94,894 new water pump, old was leaking coolant (replaced by a shop)
11/17/23 96,728 added 850cc to be at coolant tank full
3/2/24 100,676 added 1100cc to be at coolant tank full
6/5/24 103,600 heater core bypassed, had smell of coolant in cabin when running the heat
6/15/24 105,579 added 900cc to be at coolant tank full
6/18/24 106,021 added 1500cc to be at coolant tank full
6/20/24 106,244 added 700cc to be at coolant tank full
6/20/24 106,268 radiator replaced, pressure test showed leaks, test for exhaust gas present in coolant was negative (tests done and rad replaced by a shop)
6/23/24 106,854 added 700cc to be at coolant tank full, parked on angled slope, radiator topped off w/ 250cc
6/30/24 107,541 added 850cc to be at coolant tank full
7/4/24 107,760 added hose clamp to overflow tank hose connection at radiator, was leaking, added 600cc to be at coolant tank full
7/6/24 107,776 added 500cc to be at coolant tank full
7/21/24 108,187 added 1350cc to be at coolant tank full
7/26/24 108,346 added 1200cc to be at coolant tank full
8/4/24 108,400 compression test shows 165-170psi across all cylinders
8/6/24 108,400 pressure test showed lower radiator hose was leaking, replaced
9/16/24 108,618 added 1300cc to be at coolant tank full, added 1000cc to top off radiator
10/7/24 108,642 added 550cc to be at coolant tank full, added 100cc to top of radiator, after 10 minutes of idling placed a glass container under exhaust to catch drips, after 20 additional minutes of idling, only measured <0.5 teaspoon of water
10/10/24 108,642 added 650cc to be at coolant tank full, burped cooling system, measured 400cc of air was displaced w/ coolant
11/10/24 108,679 added 1100cc to be at coolant tank full

 

[macleanflood]

Have you checked the front of the engine? Specifically the weep hole below the water pump that's the tell tale for a blown seal?

-Mac

 

[Rickyd]

Does it have a tupy cylinder head? Early 0331 heads crack and let coolant into the oil.

I'd be thinking that or a heater core

 

[TheBoogieman]

My 00' had disappearing coolant with no leaks, no smoke and clean oil. Compression was good too. I had to refill the coolant overflow tank weekly, but the radiator was always full. Typical 00-01' cracked head issue on mine. Two of my three 00-01' Jeeps had this issue by 130,000 miles.

 

[1stofmanyjeeps]

Thx guys! I'll check for the TUPY head!

 

[JKP]

You can do an oil analysis to confirm coolant in the oil, but most likely a cracked head.

They crack directly under the oil cap, so you may be able to see the leak.

 

[1stofmanyjeeps]

@Syotos8889 did you happen to figure out the issue w/ your coolant loss? It seems like we're up against the same problem.

 

[1stofmanyjeeps]

It appears that I have a cracked non-TUPY head. Removing the oil filling cap revealed some milky buildup that I hadn't been seeing when checking the dipstick. I let it idle for 10 minutes, sit for 5, then opened the fill cap to find a lot of steam(?) wafting up from within the valve cover. Wiping some of the oil away from between the valves made it more apparent that coolant was sweating from a crack. Thx for the guidance everyone!

 

[macleanflood]

Going to order a Clearwater?

Replacing a head isn't hard at all.

-Mac

 

[1stofmanyjeeps]

Going to order a Clearwater?

Replacing a head isn't hard at all.

-Mac

I'm looking into my options now. It seems like it's a Clearwater w/ valves & springs for $650 vs Cylinder Head Express (Rock Auto) w/ v & s for $526 vs used complete TUPY assemblies on eBay for $400ish. Do you have experience w/ Clearwater? I rebuilt my 16v DOHC motorcycle engine a while back, I should be okay here.

 

[JasterMereel42]

Going to order a Clearwater?

Replacing a head isn't hard at all.

-Mac

What is your rec for a replacement head. I have a non-TUPY head and I know I'll likely need to replace mine at some point.

 

[macleanflood]

I'm more of an anarchist and my favorite tool is a chainsaw. Proud of the fact Ive never registered for any political party. IMHO all politicians spend more time blowing smoke up our asses than actually solving problems. Meanwhile I'm out in the woods literally picking up shit because we as a society can't solve problems. End of rant.

Never had anything other than a 97 (other than the frame and tub of a 99). IMHO everything after 97-98 got excessively more complicated.

Hardest part of a head job is getting the exhaust header off. When they moved the double cats up...ugh...I did my neighbor's 04 WJ and it took 4 hours to get the exhaust out of the way.

-Mac

 

[1stofmanyjeeps]

I'm a little worried about the fasteners on the exhaust system. I replaced an O2 sensor a while back and it put up quite the fight. For those who have replaced heads on our engines, are there particular fasteners that are more than likely to strip out? Is there anything in particular, other than gaskets, that I should order ahead of time to replace w/ new hardware instead of harvesting from the existing head? Thx!

 

[macleanflood]

I ordered a Felpro head gasket kit...came with everything including a thermostat housing gasket.

I also ordered new head studs.

And since I wasn't doing any machine work I used copper gasket spray to make up for my sins.

-Mac

 

[1stofmanyjeeps]

The FSM, using a bold typeface and capitalization, discourages the use of a gasket sealing compound. However, the hardest part of cleaning the block has been the removal of what appears to be a gasket sealing compound along the exterior wall adjacent to the tappet bore area. The residual gasket compound is only present in this area. I bought the Jeep w/ only 65k miles, so I'm assuming this application of RTV was done by the factory, but I could be mistaken. Have other people observed RTV here? If so, have you reassembled the engine with fresh RTV along the exterior wall adjacent to the tappet bore area?
Thx!

 

[Moglocker]

What is your rec for a replacement head. I have a non-TUPY head and I know I'll likely need to replace mine at some point.

I did it over the summer on my 2002 non tupy.found a rebuilt tupy head in Tampa for 400.00,new head bolts,Felpro gasket(Amazon)buy a flex socket for the cats.(good time to inspect)definitely remove exhaust ,intake is super easy then,I didn’t have a crack but the number one guide got tight,valve not sealing and was causing a p301 code.all is good now.did 1000 miles this summer to Colorado.only thing I wished I had done and will do is replace all the rockers and bridges.