Hog Rush

2000 XJ Sport 4x4
4.0L AW4 Auto
95k Miles

Repairs done just prior to my purchase:
Radiator, heater core, Alternator, A/C system, belts

Temp Hovered around the 210 mark and the electric fan would run what I thought to be too much. However we did have a hot summer.

It got a little over 210 one day and I checked the coolant level. The engine was hot but the system did not have pressure on it when I cracked the cap. It needed water and I topped it off. Temp stayed around 210 once again and I put about 1k miles on it.

Recent repairs:
180 degree tstat. When I replaced the tstat, it needed 1 gallon of coolant.

I replaced the Tstat, but still no pressure when hot. Now the temp stays around 185 degrees. Fan kicks on only when I turn on A/C.

Where is this water going? Is it possible there is a crack in the new radiator and the coolant is evaporating?

Engine runs great
No coolant in oil
no visible leaks
no vapor coming from exhaust
no antifreeze smell

RTorrez1

Check you oil and see if you have coolant in it. Your year has a 0331 head on it which are known to crack with out warning.

djb383

Have u tried a new rad cap?.....that's the only cooling system component that holds/releases pressure. T-stat has nothing to do with pressure.

Hog Rush

New Radiator cap
No coolant in oil

With all the cooling related repairs to this Jeep prior to my purchase, it makes me think a block sealer of some kind was used to try and fix a cracked head/block or gasket.

However, the coolant has to be going somewhere. I am puzzled over this one.

With A/C on, the temp does not get above 200 according to the gauge.

Runs great

djb383

U say "it needed water and I topped it off". Was that a 1 time deal or has it been low on coolant multiple times and u added water??????

Roler

Coolant loss that can not be explained, as in no visible leaks or puddles coolant anywhere, has usually less happy causes...no only like you said check the oil for coolant, but also check the coolant for oil
Compression test might be helpful: if in your setting cyl #3 and #4 are significantly low(er), a cracked head between those cylinders might be on the cards....

Hog Rush

No oil in the coolant that I can tell. One thing I did notice when revving the engine pretty high in park, the coolant reservoir bubbles a bit when it returns to idle. Not sure if this is the water pump pressure overcoming the radiator cap or more unhappy condition of compression leak.

Hog Rush

Here is the brief history of me and my Jeep:

When purchased in March 2014 the following had been replaced:
Radiator
Heater core
a/c system
belts

Upon driving the jeep to see what I had after purchase I noticed the heater would not work sometimes...the air would stay on cooler temp.
I checked it out and found low coolant.

I noticed a driveline vibe:
Bought Brown dog motor mounts
Daystar tranny mount

Went to replace the tranny mount, found broken crossmember bolts and one stripped in frame. Busy and parked it for a while till I had time to ponder a fix.

Jeep sits for a few months.

I fix Cross member bolts and tranny mount. Vibes all but go away. Happy Jeep driver.

I drive it everyday to knock the dust off it. Notice a higher than normal temp at red light. Just over 210 and fan is running like the dickens.

Low coolant was found. I noticed too the radiator cap was easily taken off without any spewing.

Here is where we are:

Changed the thermostat and radiator cap a few days ago. Still no pressure.
...and added 1.5 gallons of coolant including the coolant tank. SO now, I feel all air is out of the system and topped off. I am driving it to see if the level goes back down.

Edited to add:
New Tstat is 180 degree. Jeep temps never get above the middle mark which is 210. Mostly it hovers around 180-195.

Never before have I seen:
Exhaust vapor emitting from tail pipe
coolant in oil
oil in coolant
any visible coolant leak under or near vehicle

holycaveman

In some cases I have seen a freeze plug can leak just a little once the block gets hot. The coolant will pretty much burn off before it ever drops onto the ground.

Take a flashlight and look under the manifold on the drivers side at each freeze plug. Also look at the front of the transmission at the bottom converter area.

Hog Rush

Will do, thanks. I drive it about 65 highway miles each day and will check the fluids every couple days. The only time it ever had a temp above 210 was when it was low on coolant. Runs great.

Rockfrog

At start, pop oil cap, look down.
After drive to work, pop oil cap, look down.
10 minutes later pop oil cap, look down.
I suspect you will see green during one of those looks. It was the only way I found my Crack back in 05.
I didn't even have to coolant loss you mentioned yet.
But, if the cap is good ... The 16psi it's supposed to hold is going somewhere ... And so is the coolant.
Likely through a Crack in the head right between cyls 3 and 4 ... Sad, but likely true.
Does yours have cali emissions or 50 state? In other words do you have two manifold mounted pre cats?

skife

go to autozone, rent coolant pressure tester, pressurize system to 15lbs, wait.

Lifelong Jeeper

If equipped with an auto trans, Check your transmission oil. The OEM radiator has a tank on the side with ATF flowing through it. If it ruptures it could be sending coolant into the trans which obviously will wreak havoc.

Hog Rush

Tranny fluid looks great. New actually. I suspect when the radiator was done, it was changed as well.

So far so good. I was not able to check the valve cover for any coolant. Nor was I able to check the freeze plugs. Coolant level before making the journey home was full cold.

If I do need a head, where is a good place to purchase one with the right casting number?

Rockfrog

Heard good things about Clearwater cylinder heads, if going 0331 casting again.
If going with a junkyard head look for an 03 or newer TJ/WJ and get the TUPY casting (updated 0331 to eliminate cracking issue).
If you don't have the pre-cat manifold (50 state emissions) you also have the option to go with and earlier 7120 (91-95) or 0630 (96-99) casting.
For those you would need a 91-99 exhaust manifold and to re do the down pipe from manifold to trans crossover.
A simple strap can be made to hang the coil rail off the valve cover studs. And a new valve cover gasket would also be needed.
Otherwise everything else bolts back up.