Water in the oil 1989 XJ40.... ouch!

I need advice in a big way. My story begins …

About 5 miles from home the temperature gauge suddenly crept up to 3 or 4 bars above 90c, way above anything I’ve ever seen. The gauge did stay green (never turned red) and there was no physical sign of overheating damage when I returned. Checked the heater tank and it was empty ?? Refilled the tank with coolant and the car ran fine. Drove it around the neighborhood and it reached and stayed at normal operating temperature (one bar below 90c). Checked the header tank later and it was only half full … YIKES.

Where was that coolant going? So I drained some oil out of the sump and it was contaminated with water, it looked like chocolate milk. I performed a coolant pressure test and the pressure dropped from 15psi to about 14psi after one hour. Removed the spark plugs and used a scope to look in the top of the cylinders and there was no moisture.

So my guess is that perhaps the head gasket failed between the oil and water passages …


So it looks like the head is coming off. Since the car has 160k I really can’t complain, but I’m really concerned about what damage that water in the oil may have done. I’ve drained and refilled the oil to get rid of the contamination. The car starts right up and runs smoothly with no smoking. I only ran it for a very short period so as to circulate the fresh oil and not risk recontamination.

So …

Anyone encounter something like this ?

Is there any other way coolant could enter the oil other than the head gasket ?

I’m torn between doing the job myself and having my Jaguar Guru do it (app $2000) and a 4 week wait to get the car in ? I do have a very large garage and every tool known to man (according to my wife).

Out of curiosity is there any difference between a 4.0L and 3.6L cylinder head ? Are they interchangeable.


Sorry to hear of that mate.

Its been a long time since I had the head off an AJ6 engine, but from my failing memory, I seem to recall that the rear cover plate on the head covers the camshaft chamber and also the water jacket in the head - items 9 and 11 in this picture.


Rather a folorn hope, but I guess that a leak in the gasket item 11 would allow coolant to contaminate the oil .

BEFORE pulling the head: drain coolant, drain sump. Put on new oil filter.

Pull plugs, and fill sump with diesel. Crank the engine till you get oil pressure,and are sure the diesel has circulated.

Drain oil and drain filter, or get a new one. Refill with oil, and repeat.

This ensures no coolant sits on bearings or journals, and etches them, or causes rust on ferrous bits.

It’s also the easiest way to flush the oil cooler, if so equipped.

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Thanks guys …

Diesel oil ! … I’ve never heard of that. “Drain oil and drain filter, or get a new one. Refill with oil, and repeat” do you mean fill with diesel, drain and then with oil and drain several times ?

Do you agree that given the circumstances no matter what, the head has to come off. I can’t thing of anything that could cause the water to get into the oil other than a bad head gasket or cracked/warped head.

I eliminated the oil cooler system years ago, so no problem there.

160,000 klms/100,00mls pretty SOP for the AJ6 that’s when mine went between 5 and 6 but it sounds like yours has gone somewhere else.

Robin …

That’s the odd thing. While I was troubleshooting this I ran a compression check and all my readings were very consistent between 142 - 145 psi. I believe this sounds about right for my standard (low) compression 3.6L engine.

Diesel is actually a fairly good lubricant: it’s lubricity is higher than some oils.

Fill the sump with diesel, and by doing that, you will be getting the coolant off the bearings and other critical ferrous bits.

It will also help clean up the dreaded “milkshake.”

Based on others’ inputs, and past diagnostic experience, off with its head seems highly likely.

Yes, spot on from Sir Wiggles …

You will be fine.
It is when the motor is left in that state.
In time the aciditic nature of the glycol mix eats and ruins bearing surfaces.

Just make it quick with the diesel…it dries out seals considerably.

WalMart has 5gal jugs of oil for ~$13 for use and aid in these circumstances.

All the best to you…try and stay positive, a time just to go through things and clean up a bit…

You’ll do another 150k no problem.

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Just wondering …

How robust are these aluminum blocks ? Is there much of a chance that a cracked block could be the culprit ? While I know anything is possible is there a way to eliminate that possibility without yanking out the engine ?

While I have never owned an xj40, i am a Jaguar geek and have read on them.

That said, robust…from what I’ve read.

Warping is more likely, and that is only upon serious, rocket launch steam overheating.

Unless you have watery oil, and i don’t particularly mean milkshake, i wouldn’t consider this possibility.

Cracked blocks seem to always just pour water out from the crankcase…

Head gasket issues are quite common on these, particularly 3.6liter from what i remember reading.

Especially higher mileage.

Don’t know your displacement, but it sounds common fare at that mileage and your attention is greater than most owners.

Apparently it is common for gasket to fail at particular point above distributor and drip on it causing troubles too…

I’m sure you know this all anyway.

Jeez…despite owning almost all various model Jaguars throughout my life, EVERYONE here knows more than me…

So fwiw

Bullet proof, I will eat one if you have a cracked block.

I agree with some of the other posters that these blocks are pretty bulletproof.

I know you don’t like the idea, but if it were me, I’d go ahead and do a head job no matter what. At your mileage, it could happen at any time even if its not what is causing your current issue. While its a pain, its not as bad as some more modern cars.

Yes, I totally agree and the heads coming off.

I’ve already unbolted the intake manifold but am wondering if it’s easier (possible) to leave the exhaust manifold on the head when I remove it. I’m sure it will be a lot easier to take the exhaust manifold off the head out of the car. I can’t help but think that after 30 years those rusty nuts and bolts aren’t going to just spin right off. I realize that it would add weight to removing the head but my brawny friend and I can deal with that :kissing_closed_eyes:

I’ve just replaced the head gasket on my 4.0 and I had to leave the rear exhaust manifold attached to the head because I was rounding off a nut instead of loosening it. There was no access for a socket. My wife helped me to lift the head off ( and get it back on) and she’s only little, so you should be fine.

When I replaced the exhaust gaskets and had the manifolds planed at the machine shop, I found the manifold nuts/studs to be fairly easy to remove once I separated the downpipe …that was the most awkward bit.

I also replaced all the studs when I refitted the exhaust. I don’t see why you couldn’t pull the head with the manifolds on though, but I suggest taking them off if you can, that is a heavy bloody head!

LHD cars have better access than right-hookers to the exhaust side of the engine.

I’d recommend removing them due to weight, but if you can’t, I don’t think it would be a big deal. Most importantly, if you do try, be gentle and try not to break anything.

On my engine, the exhaust was no big deal and come off easily, as opposed to some of the bolts that go into the waterjacket.

Brett …

It doesn’t look like I have a lot of room to get in there and unbolt the exhaust headers from the head. I have a LHD and it looks like the A/C hoses are in the way.

I’d prefer to do it that way but it looks really tight. Any advice?

My only advice would be to have some Gearwrench wrenches handy and maybe some wobble extensions. Honestly, I don’t recall what I had to do on my engine to get to those nuts, but its doable even with the A/C in the car. If you get stuck, I can always go out to the garage and figure it out again for you.

Brett …

Did you get to all the exhaust manifold bolts from the top or do you need to undo some from underneath the car?

I’m very well equipped when it comes to tools and always love adding new ones, so no problem there.

As I mentioned I’m tempted to just pull the head with the headers still attached. However after getting under the car there appears to be one bolt that looks impossible to get to …


Groove, you’re really making me try to remember a long ways back! If memory serves me, I think I did access at least one of those from the top. I’m going to have to look at my setup again after work today. I really need to see it again to be able to give you advice on how I would have approached it.