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Unexplained coolant loss, but mechanics thinks the head is fine. ???

Tony the Liger

NAXJA Forum User
Location
USA
Posted this in a couple other forums. Just wanted to get as many opinions as possible.

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. 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. 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); didn't find any issues with the head at that time, 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 having it tested 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?
 
Have you tested for combustion gases in the radiator? When my 2000 did this it was a small leak in the head gasket. Just as yours, there was no visible signs other that using water.
 
the problematic head crack usually results in mixing. i wouldnt jump right to suspecting that.

if you are losing it but not seeing it... its burning off before you can see it. its either making its way into the cylinder or burning off the block. id suspect head gasket either way.
 
the problematic head crack usually results in mixing. i wouldnt jump right to suspecting that.

if you are losing it but not seeing it... its burning off before you can see it. its either making its way into the cylinder or burning off the block. id suspect head gasket either way.

I'm going to send an oil sample to Blackstone Labs, too, fwiw.
 
I had a head gasket go and it leaked coolant into two cylinders. I did notice an excessive amount of water vapor coming out of the exhaust pipe, but a cold motor will spew out some moisture anyway, just water from the atmosphere. The real tip-off was when I held a white paper towel up to the exhaust after starting a cold motor and noticed the droplets of water had a blue tint, the color of my coolant.
 
I've also had tiny radiator leaks, where most of the leaking coolant would evaporate away and never leave a telltale drip under the XJ. But they would leave whitish deposits near the leak. Behind the fan shroud near the passengers side end tank is a likely spot.
 
I just got done changing the head on my 2001 , try pressurizing the coolant system then remove the oil cap and look in side the valve cover at the head , the head will crack under the oil cal cap you should be able to see the coolant coming though a crack in the head . It will put the coolant in to the oil and the engine will run good still but it could hurt the engine bearings .
 
Check the fluid in the transmission, assuming it's an auto. If it's milky pink like a strawberry milkshake, you have your answer...
 
Replace the radiator cap
 
How much coolant loss are we talking about over how much time?

And what sort of use is the vehicle seeing during this time?
 
How much coolant loss are we talking about over how much time?

And what sort of use is the vehicle seeing during this time?

I don't drive my XJ much at all. Before it started losing coolant, I probably drove it to the store or to my parents' farm once or twice a week, amounting to no more than 30 miles per trip, max. By the time I figured out I have a problem, I'd probably refilled the reservoir three or four times. It sat for most of the winter (fired it up here and there) and I topped it off once more a month or so ago. I haven't had to add any coolant since, but I haven't driven it, either, except to get it to my mechanic the week before last.
 
Well, I had a similar problem once. Bear in mind my Renix is still closed. But about monthly I would need to top off the expansion tank. I don't drive many miles so it's not too bad to deal with.

One day while changing my serp belt, I noticed some green in the lower corner of the radiator. Not wet, but a bit powdery and slightly chunky and definitely dried coolant.

I surmised that I had a small crack that when cold sealed well enough. But when up to temp, the heat and pressure opened the crack just enough to leak some coolant.

So peak down in the corners of the fan shrouds with a bright flashlight. Look for any traces of dried coolant residue.
 
Well, I had a similar problem once. Bear in mind my Renix is still closed. But about monthly I would need to top off the expansion tank. I don't drive many miles so it's not too bad to deal with.

One day while changing my serp belt, I noticed some green in the lower corner of the radiator. Not wet, but a bit powdery and slightly chunky and definitely dried coolant.

I surmised that I had a small crack that when cold sealed well enough. But when up to temp, the heat and pressure opened the crack just enough to leak some coolant.

So peak down in the corners of the fan shrouds with a bright flashlight. Look for any traces of dried coolant residue.

Hmmm. Good to know. I'll look into that. Much appreciated.
 
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