Hey guys so I am having some problems with leaking mineral oil on my 1989 xj6. So this car belongs to my grandparents and is never driven. I try and keep it up when I can and most recently noticed all of the green mineral oil had leaked out of the car. The Jag has not been driven in around 5 months although it is started and allowed to run weekly. Around July I added more mineral oil to the reservoir and no leak seemed present. Another note is the hydraulic suspension was replaced with conventional one years ago. Last week I drove the car and the low brake fluid light illuminated and when I pulled it back into the garage I noticed the pool of green fluid. The entire under body of the car is covered in the fluid and it is difficult for me to find the source of the

Any​​​​Any suggestions? Is it possible I over filled it and after sitting for so long it all leaked out? When I filled the fluid back in July I added the plug back to the top (as pictured) should it be fit in all three holes as in the first picture or left half off as in the second picture? Thanks all for your help.
Cole

 

I always hate to see a post with so many views and no help. Let's see if I can give you a hand with your problem.
First if the low brake fluid light came on then you are low on brake fluid. The reservoir in your picture is not the brake master cylinder and the brakes do not take mineral oil. The master cylinder will be attached to the vacuum brake booster a very large cylinder shaped object on the firewall. Use only brake fluid to top it off.
Now if you will do me a favor and post a picture that is a little further away I might be able to determine what the reservoir is that you are filling. My first thought is that it had something to do with the ride control that you say has been removed, But that's guessing.

 

Hi Cole,

I think I replied to your question about the mineral oil bottle and nozzle in another thread. I didn't respond earlier to this thread because I had hoped some of our owners of early XJ40s would reply. It's been awhile since I worked on a mineral oil system, and even longer since I owned an '88 XJ40.

In your car, the mineral oil is used in a power hydraulic system that provides pressure for the hydraulic brake booster and the Self-Leveling Suspension (rear only, by now converted to conventional shock absorbers on most cars, including yours).

Vern,

No XJ40 was equipped with a vacuum brake boost system - they were all originally equipped with hydraulic assist, although some have been converted using Series III vacuum boosters. From 1990 on, the hydraulic system used brake fluid rather than mineral oil. But you are correct that in Cole's car the actual braking system is separate from the power hydraulic system and the brake system uses brake fluid.

Which raises the question, Cole, of what exactly the warning lamp says on your instrument cluster. Does it say "Low Brake Fluid," or does it just say "Brake?" If the latter, I believe that is an indication of low pressure in the power hydraulic system, probably related to your loss of mineral oil.

Here's a snip from the Power Hydraulic System Manual showing the plumbing and components (and potential leak points):



You can download the manual here:

Jaguar XJ40 Power Hydraulic System Manual

Cheers,

Don

 

Vern, I don't have that reservoir on my own car as the system was dispensed with as the model year advanced. I'm only posting based on what I've read about this system from other members with early cars.

From what I gather, that reservoir did supply the ride leveling system but also the brake power assist. I think it is still in use on cars that have been converted from self-leveling, however (not entirely sure about this) fluid can be exchanged for a more easily obtainable fluid ...more info on this in the archives.

As this topic didn't cover my own vehicle I only skimmed the posts concerning this system so please bear that in mind!

Larry

 

Thanks so much for all of the help guys so this is the mineral oil reservoir that is pictured and was topped off this summer. At the same time I bled the traditional brake system (non-mineral oil) and topped off the fluid. It is possible that the warning light is faulty as many lights will occasionally blink on after the car has sat a while and disappear after it is driven a few times. My main cause for concern is the massive amount of leaked mineral oil found on the garage floor since nothing seems to be cracked, but it also seems to be all over the under body of the car. The mineral oil "cap" has turned from green to red indicating it low so I am certain that is what is leaking I am just not sure why or from where. Should I just top off the mineral oil again and see if it leaks ?

PS: Yes Don you have helped me in the past and I greatly appreciate it. That time was when I bled the brakes and topped off the fluid and they worked great (until now).
Thanks again guys, this community is really helpful to a guy like me here in the states where not many people know too much about these older jags (at least in rural NC).

 

Just an idea but is it possible the no-longer-needed lines to the rear shocks could have come loose or aren't pinched off too well anymore?

Larry

 

Would that cause the leak from the right front passenger side (US version) near the reservoir? If so then I am sure it is possible since the initial conversion was done 20 years ago. Is there a way to test that?

 

If you know whereabouts the leak originates, (and it sounds like you do!) de-grease and wash the area THOROUGHLY, fill it up and drive around the block a couple of times, stamping on the brakes. When you get back you'll be able to see what's leaking - a split hose/loose fitting/ruptured tank or whatever. First step is to clean everything off.

With the severity of the leak you have, it should be pretty evident what's what.


Larry

 

The hydraulic pump and pressure accumulator sphere are below the reservoir, the valve block is nearby. After you've cleaned it all as Larry says, you'll be able to see the various hose fittings. If I recall correctly, it is easiest to see the pump and accumulator via the right wheel well, though you may have to remove part of the wheel arch liner.

Cheers,

Don

 

Thanks guys for chiming in. I am always amazed by how much you can learn on a daily basis with the forum.