First.
Hello all!
I have always admired these cars (from afar) and a few days ago a free xj6 fell into my lap (not literally of course).
As with all free cars, there is a catch.

The previous owner believes the headgasket is out on the car and I think she was right.

The car ran and drove fine, until one day a few weeks ago the car wouldn't start. An inspection revealed coolant near the air filter and with the plugs out, cranking the engine shoots coolant out the plug holes...

I'm looking forward (haha) to getting into the car next week and checking compression etc to confirm the head and or hg are bad before tearing into it.

Any other thoughts on where the coolant could be coming from? Not familiar with these motors, but maybe there is another place where coolant can get into the intake... Also, with about 140k miles am I better off finding a running motor from a crashed car or doing the head?

The rest of the car is in very good shape and everything works!

Thanks!

 

oliviermv:
First, welcome! Sorry it has taken somebody so long to reply to your post. The headgasket on my '91 was done by the previous owner, and it is a common fault on these cars. The good news is that when done by a good jaguar mechanic, the engine gets a new lease on life. at 140K miles, with proper maintenance, the engine should only be half-way through its usefulness. Keeping the rest of the car going around it is the trick!

If the rest of the car is good, have pay the money to have the headgasket done (along with valve seals) and for a couple thousand, you'll have real nice ride.

Others may chime in. I can only imagine that between us there must be lots of headgasket stories to go around!

Cheers,
Scott

 

Thanks for the reply midwestjag.

I'm looking forward to getting into it tomorrow morning and checking compression, etc.
I'm planning on doing the head and/or gasket work myself. I've looked at the procedure and it doesn't seem particularly daunting. Also, I have gone though all sorts of motors from small block chevys to DOHC BMW v8s so hopefully I can handle this one...
You say headgasket failures are fairly common on these cars. Do you know if this is because the head is prone to warping or if there is some other reason for these failures?
Besides valve seals, lapping, making sure the head isn't warped are there any other things you think I should do while I'm in there?
Any particular manufacturer of head gaskets for these cars I should avoid or you can recommend?

Thanks.

And hopefully I'll get a pic or two tomorrow to add to my signature...

 

oliviermv,
Sorry I cannot be of any more help. I've done all this work on my Model A, but anything more technical is WAAAY beyond my pay grade! You have raised a good question, though. Why is it that the head gaskets on these things are failure points? I'm guessing an inferior gasket material, rectified by better replacement parts. I've never heard of a head warping; but on my Ford, having the head planed is standard practice when replacing the gasket.
In any event, you sound perfectly over-qualified for this engine - should be no problem at all. It's a lovely thing - just sitting there and everything within reach.
Best of luck!
Scott

 

A fairly easy job,you will need a cam timing tool (available on the net and not too expensive) also new head bolts. On my 91 xj6 i had head gasket problems that after doing it once and it came back and had to do it again,i found that my cats were plugged up. I hogged out the ones in the manifold and put exhaust pipes in place of the ones under the car. It even passed emissions with out the cats.I would have the head surfaced and also get a big flat honing stone (one over a foot long) and surface the block when the head is off.

 

Thanks for the info on the cats. I will have to check them out while I'm under there...

Tested the compression yesterday and:

#1...105
#2...25
#3...110
#4...50
#5...40
#6...80

Those are the wackiest compression readings I have ever seen. Also, the oil and water show no signs of mixing. Coolant is clean, as is the oil. Not so sure it is the headgasket at this point, but something is definitely going on in there. I wonder what I will see once I get the head off? Burnt valves?

I was unable to get the car started even after airing out the cylinders and draining the coolant (to keep them from filling again). I am getting spark and can smell the fuel. I guess these engines don't like to be run on two and a half cylinders! Maybe I'll disconnect the cats from the system (as Lumpy suggested this could be part of the root cause) and try again before pulling the head off. Motor is close to starting and this might be enough to get it going.

I would much prefer to be able to start the engine before swapping the headgasket. Makes it easier to troubleshoot if I have problems starting it after the change...

 

Coolant in the combustion chamber seals the deal. There is no other possible cause other than a headgasket, unless of course the block is cracked though I highly doubt it.

 

Your compression readings do seem strange. For a straight forward head gasket I'd expect only 1 or 2 cylinders (adjacent) to be down.

These engines suffer from bore wash as a result of flooding (usually with fuel not coolant!). This may be a factor in your compression readings. I suggest doing a wet compression test. Putting a thimble of engine oil in each cylinder before your tests may get a different set of readings.

 

I was also expecting only one or two adjacent bad cylinders. I did repeat the test wet with essentially the same results, so I didn't post them...

I pulled the valve cover (along with the intake and exhaust) today and found lots of milky oil and even some straight coolant sitting in the low spots on the head. That is odd as the oil on the dipstick was clean... With the coolant also shooting out of the plug holes, that head gasket must be crumbling to bits in there if not worse... I'll see in a couple of days when I get to finishing the disassembly.

A few questions in the meantime for you jag experts...

1. My haynes manual says to remove the distributor as well as the camshafts and sprockets. It seems I should be able to leave the distributor in and camshafts in place, just removing the sprockets. Is there a reason why this won't work? or will it be obvious when I get deeper in there?

2. I am afraid that when I get this head off I will find it is no good. It seems like a bad sign to me that I found coolant in the combustion chambers and under the valve cover. That, combined with my compression readings, leads me to believe there is some cracking or other issue up top. The previous owner said the car was never overheated, but I can't be sure and have never heard it run... Are the heads from the 4.0L engines interchangeable or is there a narrow range of years that will work?

3. Finally, I spotted a complete (claimed to be running ...) 4.0L motor on my local craigslist from a '91. Is this a direct replacement, or are there significant changes between '91 and '93?

As always, any help appreciated!

 

Well the head is off...

and the head gasket has a break at #2 between the water jacket and the combustion chamber, and a shiny clean piston and valves... big break between #4 and #5... and signs of leaking between #5 and #6, but nothing definitive.

Looks like I may be in luck and just have to swap out the head gasket...

Still need to clean the head and make sure though.

 

Good progress , thanks for the pics

 

Wow, that's a major gasket failure. Is the head and valves intact?

 

Head gasket failures are one of the more common faults on these AJ6 engines, unfortunately. I remember some years ago reading an article on HG replacement "how to" in a magazine in the UK. The later AJ16 engine is better, I believe. Main thing is to avoid driving too far after a failure. Being an aluminium engine, the combustion gases can damage the head and block faces if left too long.

 

Having had a good look at your pics, I have to say I have never seen any head gasket quite so comprehensively trashed as that one. I also see marks on head and block between two sets of bores. You need to check these carefully to make sure they clean up with no loss of surface, because metal erosion could prevent the head gasket from making a decent seal.

There is also plenty of mayonnaise in that head, indicating you need to flush out the oil ways and the coolant jacket and pipes/passages.

Can't help thinking that other 4 litre engine you mentioned is a more attractive proposition for a swap out job.

 

Looking at your head and block,you will have to have the head surffaced by an auto machine shop,and also the block (done by yourself with a large flat abrasive stone,clean it well use some blue dyken and work the stone from front to back then back to front not lingering at any area as you want it flat). As for the distributor you will have to remove it when putting the cam sprockets back on the cams. The 91 motor will fit the 93,same motor,if you can get it cheap it most likely will cost you less than repairing your motor,just make sure that everything is ok with it.

 

Just an update...

Haven't made any progress since pulling the head. I'm in the middle of moving, and working, and a 6 month old kid... so the jag is not at the top of the list unfortunately

I was running out of daylight when I finished pulling the head so I haven't had a chance to clean it up and really check it out. I'm hoping to in the next few days so I can make a decision on whether or not to order a head gasket set or look for a different engine.

I called on the motor that was for sale and the guy sounded kind of shady. He told me the compression was perfect across the board and that the motor had about 90k on it. He had some other engines listed so I had a friend call on a different one. Of course it had perfect compression and the car it was from only had 90k on it also... Coincidence? or buyer beware? The last thing I need is to go through the trouble of installing an engine that isn't any good...

Anyway... I'll clean up and check out the block and head later this week and report back.

Anyone near san francisco have a parts car with a KNOWN GOOD motor?

haha

 

Oh...
and thanks again for all the good advice on prepping the block and head before reassembly!

 

It's ALIVE!

Put it back together a few days ago and after quite a bit of cranking, it started. Runs pretty well. No apparent leaks.
Just need to tighten up a noisy alternator belt, find out if the AC is an easy fix, and enjoy.

Wheee!

 

Good Job! Nice job huh? Your posts remind of my thoughts while going through this. Should I just get a new motor? Etc. I'm glad I got in there and got mine done as well.
I couldn't have done it without the help of friend though.

 

Lots of fun!
I thought the hardest part would be to get the head out by myself until it was time to put it back on by myself.
Definitely better to get a friend next time...
But it is satisfying to be finished.