Slow coolant leak found. But Hidden
 

I've been having a slow coolant leak thing for over a year. No evidence, tried a bunch of things, no luck.
Now coolant is low every week and seeing my first spots on garage floor. Up on lift mechanic showed me coolant drips all over bottom of transmission. He says leak looks like it's coming from behind engine and dripping it's way down. Lots of stuff to remove in engine bay even to see back there.
Can't find a thread that matches this, any ideas?
Thanks!

2004 xj 95k

There are 2 heater hoses behind the engine, from the metal coolant pipes to the heater core. You can barely see them looking down the right side of the engine under hood. Possibly accessible with the intake removed--that's a 4 hour job, not difficult, just tedious.

Could also be the heater core itself, might leak out the a/c condensate drain.

There is a dye you can add to the cooling system. Ive bought it at my local parts store. $8 -You will need a black light. Works great when the garage door is closed. Takes out the guessing game. hope it helps..

Ok thanks guys, I'll pass the info on to my mechanic.
this is above my pay grade as I don't take engines apart (I can pull a dash, but remove manifolds, no)!

I knew there were pictures somewhere: https://www.jaguarforums.com/forum/x...3/#post1327828

You can't see the heater hoses, but in the photo they are to the left of the a/c hoses on the firewall (closer to the right side of the car). That would be the only coolant related part at the back of the engine, unless it's a valley hose that's just leaking out the back. You can see in the thread above that the hose under the intake is prone to aging and you can't really see it with the engine together.

2 other possible areas to look at
 

My wife's 2004 XJ8 started experiencing the same kind of slow leak shortly after she passed 90,000 miles as well. I couldn't find it for love nor money for several months. I finally removed the expansion tank and other bits to get a clear look at the thermo housing (the original plastic type) and found the slightest trace of residue where one of the connector pipes joined the body of the housing. It was very slight but it was coming from a hairline (and I mean hairline) fracture in the housing where the inlet section of the housing met the body of the housing. Under pressure when hot the water would seep out and then when the engine cooled down the leak would stop. It was enough that over a period of several days the expansion tank level would drop and set off the low water light.

Had I not removed enough bits to get a clear look at the thermo housing I would never have found it until the housing failed completely and left her stranded somewhere with a possibly destroyed engine to boot.

Replaced the entire thermo housing and leak went away.

Well I talked to an indie jag mechanic and he said that housing (along with some gaskets) would get replaced when he lifted the intake manifold to replace the valley hose ($1200 parts and labor). I have quite a bit of coolant now leaking and it is dripping down back of engine all over transmission so I think it's probably the valley hose?
Did you have coolant dripping from back of engine? Probably my housing is cracked too, but it seems bigger than that now.
Also my leak hasn't showed up in pressure tests.

Swap the thermo housing for sure
 

I don't know if mine leaked enough water to have any get blown towards the back of the engine but if your mechanic can change out the entire housing while the intake is off be sure to do it as it's a big time hassle with the intake still mounted as there's one part of it that's tucked well under the lip of the intake.

I could not find an aluminum replacement so I think you have to go with a new plastic one. It's made in several parts that have O-ring seals at the junctions and I'd bet not one in 100 people could tell it's a thermo housing if you held up for inspection.

Got mine form Parts Geek at:
04 2004 Jaguar XJ8 Thermostat Assembly - Cooling System - Original Equipment - PartsGeek


Includes a new thermostat but I think I also had to order a couple of gasket/seals

Hi all, I've noticed a small reduction in my coolant reservoir over several months, and also recently noticed significant water puddles under my car. I can't tell if these two symptoms are related, or independent. I refilled the reservoir with ~500 ml / 16 oz distilled water, and that seems to be holding at 'Full'. With the Climate Controls off, water drips are very slow, but I noticed them increased both when I went to Full Heat and Full Cool. The car was idling, at operating temp on my flat driveway while I watched/filmed.

,I'm perplexed by the water puddles under the car. There is no orange tint, just clear water. Could this be related to the heater core lines or AC condensate drains? The water drips from the transmission/exhaust valley, hidden by heat shielding. I noticed puddles on the driver's and passengers sides, but the driver's side drainage was much larger.

Is this something to be concerned at, or standard behavior?
​​​​​​

https://cimg4.ibsrv.net/gimg/www.jag...f65179f274.jpg


​​​​​​

The rapid drip looks like my AC condenser does. As far as the small spot goes, when I observe a leak/puddle like pictured, I do the old fashioned finger test. I touch the puddle and then touch the end of my tongue. Not probably taught at any school but always tells me if it is water, anti-freeze or brake fluid. Oil I can tell by feel, usually. Not scientific and my son refuses to do it but it works. You can spit out any fluid but you only need enough to taste. It is not necessary that any be ingested. Again not scientific but if it is sweet you have coolant. (A white tissue would sometimes show green coolant but not orange colored coolant.) Many times my motorcycle will leave a drop or two of oil or coolant on the garage floor and this is how I can tell where to look for leaks in its many nooks and crannies

My experience was EXACTLY the same as RDMinor's, and it drove me and my Indie crazy. Fortunately, the Jag Specialists in Thornhill had run into similar 'ghost' leaks before, and replaced the entire thermostat "tree" as well as the hoses involved. $1,800.00 CDN, but the leak is gone, and I'm confident in the car for long runs again. Good Luck!