Hi all,
We have a series 3 XJ6 4.2 and it is leeking coolant from what we believe are core plugs, 3 of them and they are sitting between the spark plugs… However, trying to order them from Jaguar (The Netherlands) seems to not work. They say these are not core plugs and are screwed in.
I have been surfing the internet all morning to no avail, anyone knows what the plugs are called and what the part number is ??
Please check image: https://imgur.com/tNCz5Mb
Hi,
Yes they are core plugs. They are not threaded in.
Jaguar Part number - C16862/2. Though if you take measurements they are probably obtainable from parts suppliers - there’s nothing Jaguar specific about them.
I’ve replaced them on my own car. I found I had to use some anaerobic sealant on reassembly (Loctite 574). I know Jaguar probably didn’t use any sealant in the factory, but they were working with freshly machined parts. On a 35+ year old cylinder head, in which these plugs have possibly been changed before, the aluminium bore that they sit in may not be so smooth anymore.
Sadly current Jaguar dealers aren’t interested in stocking and supplying parts for these old cars anymore. Most of us look to classic car/aftermarket suppliers.
Regards,
Andy
Thanks a lot Andy!! That is exactly what I thought. We just wanted to order the parts and do the fix ourselfs but they were not “able” to help us.
They are definitely core plugs. On much earlier heads these were bolts, did you specify Series 3?
Try ordering from more knowledgeable sources than Jaguar. I would epoxy them in or at least use some sealant too.
Oh, and make sure that it is the core plugs that leak. I had a leak at one of the head stud acorn nuts and the coolant pooled in the adjacent core plug for a while…
David
Thanks Dave, w saw the coolant pooring through the plugs, so pretty sure it is them.
I have heard it said that, when replacing such plugs, the new ones should be installed upside-down from the way the originals were installed. They should be set in place dome-side out, and then you need to smack the dome just enough to deform it and firmly anchor the plug in the opening.
That is an interesting approach, anyone else confirm this ?
The FLAT core plugs are installed that way (They look like large contact lenses). My brother has a 1952 MK VII and that is how we installed the ones in the block.
The cupped ones we just installed normally.
bob
Sure look like core plugs to me. were I in need, I’d measure the opening and go to my local parts place with the picture as well.
Caveat. I’ve replaced core plugs, but ever on this engine…
Lots of stuff in most cars is “off the shelf” by the maker, not brand specific.
Carl
Echoing others, yep, just standard cup plugs.
Install as per the factory, with a wee swipe of Permatex.
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There are also core plugs on the side of the engine, Bart - with different dimensions and less accessible…
Frank
xj6 85 Sov Europe (UK/NZ)
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Dag Bart
Welcome to Jag-Lovers
It sounds like your engine has been filled with plain water and left to rust inside, instead of being protected by corrosion inhibitors in anti-freeze. The long head studs may be rusted so do not disturb them if nothing else is leaking. However, there is some good news…
Je hebt geluk want een van de beste klassieke Jaguar-bedrijven heeft een winkel in Oisterwijk:
SNG Barratt BV
(31)13 521 1552
Mvg
Pete
They are called core plugs because the holes are there to let out the sand that was used in the sand core to form the water passages when the head was made by pouring melted liquid aluminum into the foundry mold.
On earlier engines they were threaded plugs made of brass. Here is one in my '51 XK120.
Thanks Pete, I also found them and ordered with them. During phonecall the employee figured out that Jaguar NL was trying to order from them for us 
That is probably why things got mixed up at Jaguar indeed.
Do you happen to be a network engineer?
Thanks Frank, it is about the ones on top and we got them from SNG Barrat
Mechanical design engineer, now retired, but my first engineering job was at a steel foundry that made railroad car couplers, and my summer internship was at Caterpillar where they machined the raw castings for engines.
