It is an after market top and cap assembly for the header tank,which is where you are having your leak problem. It is a screw on cap with an o-ring that replaces the radiator type cap set up.



Jaguar XJ Filler Neck AND CAP Brand NEW Quality Brass | eBay

 

Paul
Do you still have this problem? If so, I suggest that you do the following things:

1. There is a little spigot that goes from the filler spout about 2 inches below the filler spout cap to a little rubber tube that goes to the RHS rad top banjo bolt. Remove the tube from the spigot and check that the spigot is not blocked. If it is drill out the blockage carefully so it is no longer blocked.
2. The check that the rubber pipe has the non return valve in it and that this is working. It should blow through towards the rad from the fill pipe and NOT allow the reverse. If this is absent or blocked, get it out of the pipe and replace. JCP still have them and they are cheap.
3. Then check that the radtop banjo to which this rubber pipe goes is NOT blocked. Also check that the thin pipe that goes across the radtop is not blocked anywhere. This is the coolant air bleed-off system and it must be free of blockages
4. Then replace the filler spout cap with a solid cap such as: Radiator Cap Valveless - Car Builder Solutions - Kit Car Parts and Accessories

This will stop your spout leaking, but only if you do all of it! Ask me how i know!!


Greg

 

I think you may have got the wrong bit identified here, I got the impression that Paul's problem was the centre filler spout, not the header tank?

Greg

 

HI guys thanks for the response I appreciate it.

Yes my leak or residue was coming from the filler spout near the centre of my engine, right near the A/C compressor. The cap I use is a blanking cap (non pressure)

I kinda lived with it up till now, checking the coolant levels periodically though.

Clarke maybe we could have a look at what Greg recommended if we have time on the 28th? I'm pretty sure we sorted all blockages though when we swapped out the radiator..

 

Paul,

Greg has some very good points and I reckon you and Clarke have covered them

The banjo on the Goose has been modified.
The valve in that hose is NOT there, as I could never get them here, and have not run them for as long as I can remember, and so far no issues, BUT, Greg is correct with what it does, and why Jaguar put it there.

I reckon that the actual spout that the blank cap screws onto is the problem, its distorted from old age and many on/off's of said cap. I have seen them distorted badly, as they are only made of brass. They are in fact, the cap section from any conventional radiator in the world, silver soldered to that upright tube. NOT specific to Jaguar in any way, or "Rocket Science". Any decent radiator mob could simply replace that cap section for you. Even the new" Stainless Steel" crosspipes still have that Brass cap bit silver soldered to the vertical pipe.

Failing that, the pressure cap on the header tank is blowing off too high, but again, I reckon you guys covered that. I run 13psi caps.

As a side thought, I do that. That screwed arrangement Clarke showed for the 6 cylinder cars, could be adapted to the V12 filler spout without too much fuss. You would have to be thinking waaaaay out there, but I reckon Clarke is real good at that, and the radiator guy would need to be out there with you.

 

They do go home quite quickly Paul. I have just changed mine as the first one only lasted about 4 years. Grant's idea of taking the spout to a rad shop and having a screw top type fitted is a very good plan, IMO.

Always a job on an XJS!

Greg