Hi,
I've got a 1986 xj6 series 3.
For the last couple of months it's been losing water, a mechanic looked at it and pressure tested it, but found nothing.
The expansion tank cap seal wasn't great so I replaced that, there isn't any "mayonaise" on the oil filler cap (I'm praying the head gasket hasn't blown).
If anyone's got any ideas, I'd be really grateful.
Many Thanks
Geoff

 

Perhaps all is well. Lose a little or perceive a loss, add more. Too much! Jaguar bleeds off excess.


Carl

 

Jag cad is right. I have same issue and just add more every now and then and I don't worry.
There are alot of voids in motor that can suck up water when it gets hot or under a load.
FYI. head gaskets can blow many ways. water-oil, water-piston, oil-piston, piston-piston. There are lots of ways to check all this, but if a you did a pressure test then you don't have water-piston or water-oil.

 

Check all the hose clamps,,, then watch the exhaust pipes after the car is at operating temp...if there is steam coming out of the tail pipes ,..you may have a failing head gasket. Those are the symptoms. When cylinder pressures are high, the coolant is being forced into the combustion chamber and being steamed off . If you have a steep grade in your area drive the car up the incline at slow speed 30 mph or so, watch for steam from tail pipes.

This is one of the major shortcomings of the car (failing head gaskets) as well as windscreen channel rust.

 

Is there pressure in the coolant jacket when the engine is cold ? Undo the cap when it's cold and listen. There should be no release of pressure. If there is, it sounds like head gasket failure. The normal mode for these is combustion chamber-coolant jacket. Getting coolant in the oil is unusual because the oil supply to the cylinder head is via an external pipe. The only other oil passages are at each end of the head for drainage, and are far away from the coolant passages, or the cylinders.

 

how do you know it is losing water? do you see a puddle or leak under the car?,

is it "consuming" the coolant?, the level has gone down everytime you check it?

these cars require a huge amount of coolant.

Next time you check it,

1) drive the car until engine is fully warmed up, at least 30 minutes of driving it, so the thermostat has gone through all its open-close cycles and the temperature gauge reads "normal".

2) turn the HEATER ON to maximum heat and drive it another 20 minutes,

3) park the car LEVEL, leave engine and heater running, then with a thick towel to protect your hand and face, slowly open the expansion tank Cap (very slowly so the pressure is released slowly and until there is no more pressure being released). Then you can remove Cap, still with Heater in MAX and engine running.

4) add coolant ( 50/50 coolant-water mix), until full, allow system to swallow it and keep adding coolant until the level stabilizes. and remains at the "neck" of the expansion tank. Replace Cap.

Remember, you are doing this with engine running and heater ON in MAX HEAT, keep your hands away from the belts and fan.

Then turn off Heater, turn off engine, system should remain full now.

Next time you check it, engine should be COLD, you can add a more coolant if needed.

 

I had a similar set of symptoms on a car last year. Everything seemed normal , pressure tested OK but used water slowly but steadily. Ended up being a pin hole leak in the radiator, hidden behind the shroud. Coolant would slowly leak and evaporate , leaving a crust that would sometimes form and sometimes fall off.

 

How much loss? Does the loss seem to occur soon after topping off, and then stop? In other words, will the level keep dropping day by day ....or will the coolant level eventually stabilize?

As mentioned, you might be over-filling. Are you filling the brown tank right to the top? If you are, stop. It is not intended to be filled right to the brim. The excess coolant is being pushed out of the brown expansion tank and into the overflow reservoir in the wheel well. Leave the brown tank half-full, check it every day for a week, and let us know if the mysterious coolant 'loss' has stopped.

Many Ser III XJ6 coolant leaks have been 'repaired' this way

If the level keeps drop-drop-dropping with no end in sight then that's obviously a different matter....and others have given you good suggestions.

One good way to confirm a leaky head gasket is to find a repair shop with an exhaust gas analyzer. Have them 'sniff' the coolant for hydro-carbons.

Cheers
DD

 

Thanks very much everyone.
I'll let you know how I get on.

Thanks again for the brilliant advice
Geoff

 

My XJ6 has been using(or losing) 200-500 mls of coolant a week. Not enough to cause problems, but enough for me to check it every few days. I have even driven it to Sydney(1000 km) without a concern.

Last weekend an old mechanic mate of mine I've known since we were 6, and not seen for the last seven years came over for a few coldies and ended staying the weekend and playing Jags & bikes in my garage. (none of the last paragraph is relevant of course)

Anyway over the course of two days I think he had a spanner on every nut and bolt on the car and found a lot of small things I have overlooked. We got to the cooling system and his first question was "how much coolant is she evaporating ?". My response was it uses a bit.

He said you have no cap on your overflow bottle from the expansion tank, in this climate you will losing a couple of hundred mls of coolant a week just from engine heat under the bonnet. So he made a cap with a hole big enough for the overflow hose and said see how that goes.

This past weekend I covered 1100km in 3 days and lost about a thimble of coolant. You can see from the pics I put a black mark on the overflow bottle on Saturday and checked today after the car had completely cooled and it had only dropped a gnats dick. And the filler tank level and the expansion tank level were normal.

Just another idea.

 

".....had only dropped a gnats dick" would that be the International Unit of gnats dick or the US standard?

 

Way back when I was an apprentice printer a "gnats dick" was an official measurement according to the foreman. Everything had to be adjusted by just a gnats dick.
And I still give things "just a gnats" when the adjustment is smaller than just a little bit. Actually it is so small it can't me measured on a metric micrometer.

 

the term I grew up with that described this fraction was a "**** hair". can't use it to much anymore as people get so freakin offended.

 

Amaezing:


Yep, I am familiar with the term. As the engineering world has gone coed, I wonder how they deal with that measurement?


And, I have a vague recollection of a Gnat's a.. as another measure.


In the modern world of PC, I guess it's "close enough for government work".


next to blondes, I always had an affinity for red headed women.


Carl

 

I sorta like. Looks good from my house!

 

Many Thanks,
I haven't had a chance to look at it yet. (Just keep filling it up.)
As soon as I do,I'll let you all know.
Thanks again

 

A 1986 car will have the slotted block, which doesn't crack between the bores but the head-gasket is only reckoned to last about 80k-90k miles. And of course it fails between the slot between two bores and one or both cylinders. Hence the coolant gradually disappears. Of course other avenues for loss can open up. Where the water passage from the water pump into the block passes through the timing cover, corrosion of the aluminium cover can occur, but in this case the coolant goes into the timing chest and into the oil. I don't think this is your problem. However, bear in mind with an old engine like this, any place where aluminium corrosion can occur near the coolant circuit can allow coolant out to wherever.

 

Hi,
It turned out that one of the core plugs was leaking. (I don't know why it didn't show up in the pressure test).

Thanks again for all the help and advice.

Happy New Year everyone.

 

Thanks for letting us know. I hope the job wasn't too difficult as there isn't a lot of room to insert then hammer tight a core plug. It is easy if the engine is out, of course.

 

Core plugs. Right on. the real term, not freeze plugs.
they don't pop in a freeze. Been there, done that!!


There are core plugs that do not rely on a BFH to seat.


Saw an application on reality TV the other day. The Kilcher
family in Alaska! Generator on board the "Constructor", blew one out and quit making volts!!


The replacement core pug used bolts to expand it into the seat.
Slick. Useful, as that application was also in a confined space with no room to swing the BFH!!!


Carl