Vanishing coolant - 2001 XJ

[mbalbritton]

So my kids XJ has me a little perplexed. She’s having to constantly add coolant to the reservoir. Oil is clean, trans fluid is clean, no white smoke, no detectable leak that I’ve found yet. Engine runs fine, runs consistently at 210 no matter the weather or driving conditions.

She’s replacing it often enough that we should see a leak/drip/puddle… but I have yet to find anything of the sorts.

Only thing I can come up with is that there’s just enough of a leak in the head gasket or crack in the head that it’s getting into the combustion chamber, but not enough to see white smoke.

 

[Bebop]

Don't guess, just pressure test the system.

 

[Caver Dave]

Only thing I can come up with is that there’s just enough of a leak in the head gasket or crack in the head that it’s getting into the combustion chamber, but not enough to see white smoke.

Don't guess, just pressure test the system.

I concur, unless XJs lose coolant like Cummin's "make fuel"?

 

[Jeff B]

check to see if it's wet under the passenger side carpet.

 

[77GreenMachine]

If it has the 0331 head casting it’s probably got a cracked head. It’s super common on later 00 and all the 01

 

[shawn]

Water pump will leak coolant at the weep hole that then evaporates. Won't leak when sitting unless you put it under pressure.

 

[Croatan_Kid]

I was going to say head casting or cracked head. I've seen some crack near exhaust seats and steam off coolant, but with zero signs of white smoke. The water pump is an idea too.

 

[Shreddinlettuce]

The thermostat housings on 4.0 leak a lot due to the block machining leaving tool marks

 

[Buddy Holly]

I would bet water pump small leak or it’s a cracked head. I had a 2.5 that did exactly this. Ran great, but you had to put a little coolant in it every month or so. Never could find the issue until we rebuilt the engine and had the head magnafluxed. It had a tiny crack between cylinders 2-3.

Usually you can see a small amount of white residue under the weep hole on the WP if it’s leaking and evaporating off.

 

[ghost]

There are all your possibilities listed in this post but if it has the factory head it’s likely cracked.

 

[mbalbritton]

Follow up.

Finally found the leak. It was the core to tank seal in an obscure location to be able to see. Actually couldn’t see it, but once I found the trail I was able to follow it far enough to know what it was.

I swapped in a new radiator, made her help to learn how, and off she went.

 

[Caver Dave]

made her help to learn how, and off she went.

Wondering which was the benefactor of this knowledge? Guessing either #1 or #3, because #2 could've likely done it herself!

 

[mbalbritton]

Wondering which was the benefactor of this knowledge? Guessing either #1 or #3, because #2 could've likely done it herself!

#2

1&3 would never have even noticed they had a leak.