On the side of the 4.2 engine in the middle beneath the exhaust manifold is a plug. What is it? Mine is leaking. Does it explain why I'm losing a few pints of cooling water over 100 miles.
Appreciate any advice.

 

That is a welsh plug, replace it

 

And also known as a "core plug", at least they are here in England. It is there as part of the manufacturing process for the block. There are two types depending on age of the engine. Early ones look like a dished circular washer or plate about 1.25" across. Later ones are harder to describe, but have a U-shape cross section, with the bottom of the U dished. Both are inserted into the hole with some sealant and then wacked with a mandrel and hammer to squash the dished part and thus expand the plug so it fits up tightly and seals the coolant jacket.

 

If my memory serves (which it often does not), you can buy a replacement plug that will not require hammering into the hole, it uses an expanding-type plug...Made by Dorman , manufacturer of many "generic" parts....I believe NAPA sells them...
This will save much time and expense.
Edward

 

Thank you guys. I had the coolant system checked out by the tech at work this week. I need a new rad and a top and bottom hose. Both my Jag tech and Land Rover tech both said leave the plug alone until after the new rad and hoses are in and see how much of a leak the plug has before deciding.

 

Hi,
"Both my Jag tech and Land Rover tech both said leave the plug alone until after the new rad and hoses are in and see how much of a leak the plug has before deciding."

That doesn't make sense! Is that "core" plug leaking or not? If, it's leaking, it needs to be replaced and probably the others, as well. Was the rad in bad shape and leaking?
Sounds to me like your wallet has "leaked" funds spent in the wrong direction. Or else, you are not revealing " the rest of the story"....
I just hate to see a professional take advantage.....

 

You have a problem, not small. Core plugs leaking, radiator and old hoses. You probably have a block full of rusty settlements which need flushing. once flushed and new radiator and new hoses, plug will leak more. I was on my way from St. Louis to Terre Haute , Ind. in 1966 in a 1957 XK140 MC Coupe,I got as far as Collinsville, Il., when the back core plug ( the one between the block and firewall ) let loose. Had to be towed back home. Pulled engine to replace all plugs and made the trip 2 months later. Do it now, before the Tennessee summer, so you won't regret it.

 

Thank you everyone. I guess I should clarify. On inspection, the core plug has a slight weep. The rad and hoses have to be replaced. So we are going to replace them, flush out the system and then see what the core plug is doing. If it needs to be replaced we will. The other five plugs are bone dry. I trust my Jag tech totally. He's been working on my Jags for twelve years and he's never lead me down the wrong path.

 

Jaguar had an official recommendation to put in a can of Barr's Leaks when the coolant was replaced. This stuff sealed up all those little weeps like you have. There are other products available like K-seal. As an old design, there is no problem putting in products like this, as it was common practice 50 years ago, and the XK engine started production in 1948.


However, Jagfixer isn't wrong, these XK engine blocks have very poor coolant circulation and it is worst at the rear of the engine. A lot of crud does build up, believe you me, as I have seen it when cleaning a block when I rebuilt an XJ6 long stud engine. As I had the bare block on an engine stand, I removed all core plugs and replace them when I had a clean coolant jacket. The amount of crud was unbelievable !