I haven't been able to get to the shop yet. The same situation has happened twice more. The shop I was recommended was booked up on the days I could part with the jeep so I've had to wait and try to limp it along. It'll be dropped off tuesday morning and hopefully it'll end with a cheap resolution. I'll post results when things are figured out.

 

You said, "I turned on the heater to cold air". Do you mean, you turned the heater control to cold, or you turned on the heat, and cold air come out?

If cold air came out, either no antifreeze in heater core, or control not working, or blockage.

If you have been running for some time, at hot temps this time of year, I would install a new thermostat for sure.

If your hose is soft, time to replace...

Until you can get a repair, you can run with the rad cap in a loose position. Any excess antifreeze should still travel to the overflow container.... I ran a 1500 mile trip like that, putting in water every 100 miles,, small leak.
..
good luck...

 

Bob - the heater was set to hot, but only cold air came out.

I stopped at another shop today and he's thinking pretty much that it's either full of sludge or that it might have a cracked cylinder head. He's going to have it next tuesday and he's going to do some compression tests and a radiator flush at least.

What sort of money is this going to cost if it ends up being a cracked head?

 

I have not read of any cracked heads on the XJs, but several cracked head gaskets. A cracked head gaskets can make for over heating
problems. Hot gases get into the coolant, causing excess heat which boil away your coolant.
Hopefully the compression test will give you some answers, and a system
flush is always a good thing.
I do not know what a shop charges for anywork, since I do my own
repairs...
good luck..

 

Cracked heads are not common on that particular year model, unless you have a late year model that came with an 0331. I haven't seen and 0331 head on a 99 but I have read that it might be possible.

Aside from that, a bad head gasket could be the problem. There is a "block" test that can easily be done first. The test involves checking for exhaust gases coming out of the radiator, which would tell you a combustion chamder has found a way to get to a coolant passage. The tool I used to do this involved a glass tube with a one way valve on one end. That end is placed on the filler neck of the radiator and the tube is filled with a blue chemical. While the engine is running, and if exhaust gasses are present in the coolant, the blue chemical will turn green. This test will not tell you wether the head is crack or if it's just the head gasket. But once you determined there is definately a problem the head has to be removed. People will tell you this is easy to do, and the process seems simple, but it's time consuming. At repair shop prices it could cost a couple hundred dollars. If it's not the gasket ($50) then the head must be suspect and it will need to be checked for cracks. Replacement heads and related parts could run upward of several hundreds of dollars.

But let's not put the cart before the horse. If your coolant is low the heater inside will not work. If by filling the radiator back up causes you to have heat inside again then it's not clogged- no need to start needless work tearing that apart.

It sound's obvious you're losing coolant somewhere, you just need to find out where.