My 2000 xj is losing coolant, with no visible leaks. I know about the head issue. I pressure tested the system, lose 1 to 2 lbs in a minute or so and it keeps dropping. Tested cooling system with Lisle test kit that tests for combustion gasses in the cooling system. No gasses present. Oil looks good, no milky substance under oil cap. Ordered a oil analysis test kit to find out if coolant is present in the oil. I thought if coolant is getting into the combustion chamber it would show in the coolant test? Stumped. Any ideas?

 

How fast are you losing it?

I'm interested in what you find... I lose about a 1/4 of the overflow thank between oil changes... no other adverse signs either.

I too sent off a sample to Blackstone.

 

Coolant is going somewhere, if it's not ending up on the ground, it's in the engine. Have you performed a compression and/or leak down test?

 

No leak down test, will perform compression test this weekend along with charging the cylinders with air .

 

compression test is not a good test for a cracked cylinder head. Oil analysis test should tell you what you need to know but in the meantime you may want to start looking for a replacement cylinder head. What is the oil pressure at hot idle? That will tell you if you need to look for a replacement engine and not waste your money on a new head. If the test indeed shows no coolant in the oil, then you must have an external leak.

 

I had a Freeze plug/Welsh plug on rear of block, leak coolant into bell housing. Daily driving would evaporate coolant, no drips. Let it sit in the garage for two days and it dripped from bell housing.

 

Compression numbers are as follows 1/154,2/163,3/163,4/163,5/149,6/163. Plugs look even colored. Charged each cylinder with 100 psi, looking for a bubbling cooling system, nothing. Oil pressure is good at idle, 40 to 50 running.

Once the oil is checked out I will know a definite answer. It's not being used right now, doing a transfer case rebuild at the moment. Sad thing this rig only has 89000 miles on it. Transfer case must have had a tough life before we bought it.

 

Try a leakdown test too... I've heard of a pinhole in the radiator end cap before..

 

I had a hose clamp work slightly loose, just enough to let coolant dribble out when pressure built up. It would immediately evaporate so it never dripped. Found it by pressurizing the system and watching very carefully.

 

Since it's a 2000, search "0331 head".

 

Somehow or another, coolant is getting into the cylinders and being burned.

Not a lot. Yet.

The head probably has a small crack in it, that will get worse over time.

You can either put up with it for now, or replace the head with a brand new aftermarket one.

I'd probably do it sooner than later, so the coolant doesn't get the bearings.

 

Oil test came back, nothing abnormal. Oil is in great shape. This leads me to believe you are correct, it's burning in the combustion chamber. Looks like time for a new head. Thanks!

 

Is the inside of the exhaust pipe slimy/sticky?

 

It MIGHT only be the head gasket, but with a 2000 original head, it IS a good idea to replace it. The money you would spend at the machine shop to true up the factory head, etc. is better spent on a TUPY or other replacement head.

 

One thing I've experienced on my 2000 is on a hot hot day sitting in traffic the pressure in my radiator built up so high that I lost a huge amount of coolant just from being pushed into my overflow from the radiator cap, and by the time the system cooled down and reclaimed what was left in the overflow it didn't quite have as much as it should.

I think this could be a result of a worn out cooling fan, electric and mechanical. Perhaps something you might want to consider.