Tony the Liger

I have a '00 XJ @175k miles. I've owned it for a couple years now, but have barely driven it. Bet I haven't put 500 miles on it since I bought it. I'm losing coolant, but I can't figure out why. My immediate worry was the dreaded head issue, but aside from the coolant loss, nothing else suggests that I have a cracked head. Runs well, doesn't knock or rattle, stays cool, doesn't smoke or smell, exhaust looks normal. Last year, I had a coolant leak that I could see; I had it pressure and compression tested (to help find the leak and check on the head) which revealed that the head was fine, but my water pump was leaking. I replaced the water pump, fan clutch, thermostat and radiator cap, and I haven't seen any leaks since. I haven't driven it much at all since then, so while I know crazier things have happened, the idea that I somehow developed a head crack after a good compression test and little driving seems pretty wild to me. Still, I'm losing coolant somehow, so I took it to my mechanic last week. He ran another pressure test and couldn't find any leaks, but he says based on the way it runs, sounds, smells, etc., nothing makes him think there's a problem with the head.

So, where's the coolant going?

TrailerTrash

How fast is it disappearing?

Tony the Liger

Hard to say because I drive it so sporadically. I know this isn't scientific, but I can get a few drives out of it before I have to refill the reservoir.

TrailerTrash

Is the floor or carpet wet under the dash?

Tony the Liger

No, not that I've noticed. I'll double check though.

PatHenry

It's possible that you just had a lot of air in the system after the water pump replacement - excess air works itself out and might look like coolant loss considering how little you drive it.

If the oil looks good (no milkshake, no green color) and you can't see any head cracking (look up what the 0331 head crack looks like.. sometimes folks can see it with a flashlight looking through the oil cap hole in the valve cover).. I'd order a lab test just to be safe, but then drive it around, see if the need to refill the reservoir goes away or not. If you see ANY other signs of head crackage - stop running the motor and swap the head to a TUPY or Clearwater.

In the case of an 0331, a lot of folks will say it's reasonable to change the head out simply as a precautionary measure rather than live in fear and uncertainty of the defect showing up.

I had a 00 4.0L that I put over 300k miles on, still has the original head and still runs perfectly even after sitting for 2 years.

Red1992XJ

Did you check the ends of the hoses? Sometimes the original hoses can crack and seep slightly at the end.

Do you have any spots of coolant drips on the ground where you park it?

When you replaced the thermostat, did you purge all the air out of the system?

Red1992XJ

Wow, three at the same time.

How many times have you had to refill the reservoir?

Tony the Liger

I did my best to purge all the air after the work I did, but I'm no pro, so I won't swear to have been mistake free. Still, even if it were air in the system, where would all the coolant gone that I've repeatedly added?

Last winter, when I first noticed this, I checked the oil fill cap and did see some nasty looking foam. I was pretty convinced at the time that I had a head issue, all things considered, but I did some research, talked to some folks who are more knowledgable than me, and described what I was seeing to every mechanic who'd take the time to talk to me, and they all said that what I was seeing was condensation in the cold months, and not coolant mixing with the oil. FWIW, the oil I could see looked fine, I couldn't see a crack, and I haven't seen any of that foam/condensation since.

Tony the Liger

Yeah, I've checked every hose I can reach and haven't noticed any problems. No spots on the ground, and I've kept it over cardboard to help me see, just in case. I did purge the air as best I could.

EZEARL

He could also have a test done that checks for exhaust gases in the coolant. From what I understand this 0331 head crack can start very subtlety.

Tony the Liger

I'd say three, maybe four times. But again, I don't drive it much at all.

Tony the Liger

I don't know the first thing about this. What would I ask for? My mechanic still has it, so if he can do it I may tell him to before I pick it up.

PatHenry

Sounds like it's time for a Blackstone labs test. It's like $30 and you send them in some of the motor oil and they send you a full analysis. If there's coolant in the oil, the lab test will show it.

If you purged/burped the air as it sounds like you have, 3 or 4 reservoir fills seems pretty excessive - If it's not seeping out of a loose hose or leaking out of the heater core (wet passenger floor) then it's got to be being consumed by the engine. A compression test isn't sufficient to prove the head isn't cracked.

Another thought is to grab a coolant pressure test tool from your local parts retailer (usually free, you leave a deposit until the tool is returned) and put some pressure on the system. This will expose any external coolant leaks pretty quickly. If you pressurize the system (using the tool) and there's no obvious leaks, have a helper fire up the engine and see if you get the white smoke right after...
The coolant has to be going somewhere.

EZEARL

Ask him to do the test. If he doesn't know about it Google has many videos on it. Also if he doesn't have the tester it can be rented at most local name brand auto parts store. Always test before spending money on changing out parts.

Here's a simple explanation:
https://itstillruns.com/test-exhaust...t-7885485.html