I just made a trip of about 850 miles yesterday. My 92 XJS ran great all the way but about 100 miles to go I discovered a coolant leak. Temperature was holding steady so I found some emergency water and pressed on not wanting to be stranded. Temp gauge maintained normal position all the way to my destination. The coolant was dripping from the cross member beneath the engine and I cannot see the source of the leak. Best I can see is coolant flowing around the front of the drivers side exhaust manifold. Most of that boils off but the flow is increased from last night and seems to be coming down the drivers side of the engine block. Car ran well the entire time.

Today, engine has no power, sputters and coolant flow is increased. I guess I just barely made it and now that the engine has cooled the leak has gotten worse. I fear this is a head gasket or some other serious issue. Difficulty finding the exact location of the leak is today’s challenge. Any advice?

 

I can't decipher if the engine in your car is the I6 or the V12.
Not that I claim expertise in either! I do not.

Expertise (?) in blown head gaskets, oh yeah!!!!

!. A water pump or hose is leaking and spraying on the electrics and cause the engine to run poorly. Sure hope so.

2. Remove spark plugs and see if any are really clean!! Hot steam and water cleaned!!! Bad.


3.Fill up the system. Run the engine and look for gurgles and bubbles in the coolant. Also bad.

4. Have the cooling system pressure tested. Failing to hold pressure? BAD.

Carl

 

 

Hi gccch

Pull out the 'dipstick' is there any sign of the Oil taking on a 'milky colour' ?

Undo the 'oil filler cap' is there any sign of a 'milky colour' in or around the Cap?

If there is then that could be bad news!

 

Most automotive stores have dye for coolant, with a blacklight its clear to see, you could also remove the top atmosphereic hose at the filler neck on the coolant resv and pressureize the system till you see whats going on.

 

 

Hole in the water rail maybe. You may have to remove a few bits and pieces to locate the actual source BEFORE you settle on head gasket as the problem.

 

Very unlikely to be the head gasket. It is much more likely to be a coolant hose or seal of some sort. Go to the store and buy a coolant pressurising kit, and you will soon find it. My money is on the crosspipe short hose to the block, just under the tophose/thermostat casting. After that, a leaking water rail/water manifold gasket. This will happen to ANY V12 that has not has its 14 hoses changed regularly/at all!
Loss of power etc could well be water in the ignition system somewhere. If your pressure test shows coolant coming out of the head/block gasket, it is a very big job because of the possibility, even likelihood, of the head being jammed to its studs.

 

These last two comments are encouraging. As I am not too familiar with this engine and have read some of the horror stories I may be panicking too soon. I also can’t figure how the water I did see above the exhaust manifold could get there if it were the head gasket??? So I will get a pressure test set up and dig deeper. I really do not wish to do the head job and would sooner part out the car. With only 53k on the car it sure would be disappointing for the engine to fail so severely. The low mileage was what drew me to buy the car to begin with....

 

I hear you on the low mileage, however, there's a lot of rubber on these cars..hoses, bushings, etc. Those parts don't care how many miles on the car, but they do care that they've celebrated 26 birthdays! Unless someone has gone through the car and replaced those rubber parts, you'll have more problems. Hopefully this one isn't too severe.

Good luck! The engines have proven reliable as long as you hold up your end of the bargain.

 

I don't think there is a substitute to climbing under the car with a big flashlight and finding that leak. Because it's 'serious' - you should be able to see it. Hopefully it's some cracked rubber house that opens-up as pressure builds up.

 

I'll chime in that it is very unlikely to be a head gasket, just not at all common on the V12.

If you have the time and money, buy a pressure tester. They are great to have around and make finding leaks a lot easier with the fan off. Fans aren't blowing stuff around and you can hear bubbling sometimes.

There are a good bit of hoses on the V12 and with it moving you could get coolant moving anywhere. Unfortunately we can't be of much help here. You will have to poke around and look for the leak. If you can't find the source but can find leaks, wipe it all drive and re-pressurize for a bit to get it started again.At the front there are several hoses, and the top hat seals in the coolant pipes over the exhaust can leak as well.

what do you mean by "coolant flow is increased?"
Like it is leaking more? It's leaking more but you still can't locate where its coming from?

 

 

Hi

gccch

No signs of any water in the oil is good, so it doesn't sound like a Head Gasket but I did have a similar leak myself, which took me a couple of Weeks to track down and fix

The leak was coming from underneath the Front Closing Panel, which goes over the Top of the Radiator where Water was flowing along the top of the Rad and then dripping down onto the Front Cross Member

Which sounds very similar to what's happening with your Car, as water was leaking out around Copper Washers, that the Banjo Bolt goes through into the Rad

Or it could even be a leak from the Header Tank

If you have a look at this Post on my 'Cherry Blossom' restoration thread, you would be able to see the 'Banjo Bolt' and Copper Washers that I am talking about

In the event that Water may be leaking from around the 'Banjo Bolt' its always best to renew those Copper Washers (I would say essential)

But a word of Warning! Do not over tighten the 'Banjo Bolt' or you could Strip the Thread in the Radiator

Here is a link to that thread that may give you some ideas, in the event that what you are trying at the moment doesn't solve the problem Mystery Water Leak on 'Cherry Blossom'

 

 

Hi

gccch

Earlier on you mentioned a loss of Power, this could be down to what could be a problem with the Marelli Distributor, where underneath the Distributor Cap

You may find that the 'Rotor' has burned through, which could then have Shut down one of the Banks of Cylinders

Under the Distributor Cap, the Rotor itself is 'Stepped' where one Blade works one Bank of Cylinders and the other Blade works the other, as the V12 is very much like 2 Six Cylinder Engines joined together

In the event that the Rotor burned through, then it could cause what is known as a 'Marelli Fire' as Fuel continues to be pumped into the hot muffler/exhaust pipe of the Bank of Cylinder that had just shut down

If that is the problem and you continue to drive her, your whole Car could go up in flames

So best to remove the Distro Cap before you go any further and have a quick look in order to check that the Rotor is ok

 

 

 

The crossover pipe connects the water pump to both cylinder banks. As you can see in the picture, there are three rubber hoses that connect the crossover pipe to the engine. Any of these could be your culprit as they are probably the most overlooked hoses even when one goes to renew the rubbers under the hood.