I have been having issues with air ingress into my cooling system. After numerous checks we were unable to determine the source of the air or combustion gas ingress. Today I removed the passenger side valve cover to replace a leaking gasket. I observed rust and dust particle on the rear cylinder. It appears there is a what I believe is a frost plug next to the spark plug and it may be leaking. I have attached pictures. I would appreciate and comments on if this is a frost plug, has anyone had a similar problem and how would this plug be replaced?
Keith

 

Well, I have to say it certainly looks like a core plug. These things are normal engineering practice to allow complex castings to be produced, and the hole for the core is then sealed with a plug that should last the life of the engine if coolant maintenance and replacement is done correctly. The main problem you may have is actually finding a replacement. Replacing is normally fairly easy, I have done it on an old XK engine block with no problems. You first drive a hole into the plug then skewer it out, clean the aperture then tap the new plug back in with some sealant.

 

My best guess is that you are getting water from the windshield scuttle collecting on the spark plug well. If you are running a proper mix of water/antifreeze, there should not be the flat-on rust as we are seeing in that pic.

I suspect the rust is coming from the spark plug base, which looks really bad. I would vacuum up all that rust, and take a careful look at the freeze plug.

 

Ooh, excellent point. You can test the integrity of the plug with a cooling system pressure tester. Pressurize the system to the rating on the reservoir cap.

If the system is intact, the pressure will hold for at least 15 minutes. Inspect the plug for any signs of leakage. Since the plug is high on the engine, you might have air escaping during the test, not liquid coolant. Spread a little soapy water on the plug and any leaking air will create bubbles.

 

Thank you for the replay and sharing your experience. I have ordered new core plug from Jaguar (4 day delivery from there warehouse). Lookin9 at the installed core plug and it appears that it may be threaded into the cavity. This will be confirmed once I receive the new core plug. Any further comments for removal and installation?
Thanks
Keith

 

Have you run a pressure test to see of the existing plug leaks yet? Also, plugging the spark plug hole to keep debris out of the cylinder would we a wise idea, if you have not done so already.