Hello, I'm new at this forum and I'm so glad to join you, can you please kindly help me with this doubt? I'm restoring my XJS V12 1988 coupe right now and I would like to know the exact function of the water valve EAC4126 located at the filler neck in the water bypass pipe EAC4191 I would like to know if this valve could cause overheating problems , can I simply delete it??? mine is stuck and covered with rust, I already bought the new one of course but I'm waiting for this part to arrive because I'm so far for USA or ENGLAND, I leave in VENEZUELA (SOUTH AMERICA) and here does not exist any Jaguar dealer, thanks in advance and sorry if my english is not as good as yours, regards! Frank.

 

Frank,

Welcome to our world. When you get a minute, go to the "new members area" and do your intro. It keeps all the Moderators warm and fuzzy haha.

That valve MAY cause issues with bleeding air from the system, and most (all of mine) have deleted it long ago.

Overheating is more than likely sticking thermostats (very common), bad pressure cap on the header tank (also common), and of course a blocked radiator, internally and externally (very common).

The atmospheric bottle (inside the panel behind the LHF wheel) is also well documented to be full of mud, and this stops the system from venting the excess pressure as designed.

Then comes the actual bleeding of the air out of the system, this can be a mongrel on some V12's, and if it is not 100% bled it will overheat every time.

The lsit goes on, but that is the basics.

 

Today's my lucky day. I've learned something new for the day, which is something I strive for, and I haven't even finished my first cup of coffee!

I never knew this valve existed...and I consider myself fairly well versed on 80s-vintage XJSs. I had to look it up in my parts catalogs.

Just proves that you're never too old or too experienced to learn something about a Jag XJS.

Or anything else, for that matter

Cheers
DD

 

thanks my friend, why you think Jaguar engineers put this valve there

 

To keep the Forums active!

 

Bloody comedian, BUT true.

There are many things on many cars that confound enthusiasts at some time in the future, and we only scratch the surface mostly.

Take the V12 starter motor removal on a RHD car. There is a bracket welded to the crossmember that does nothing, but stop the removal of said starter motor, WHY, coz they can.

That valve originally was a anti bleed back arrangement, but the upkeep of the system coolant specification was critical to prevent rusting of it, and as we all know, maintenance on V12's is sad at best when we enthusiast types get our hands on them, mmmm.

The "upper" seal of the central coolant cap is CRITICAL, as is the header tank cap seal/s. If they are marginal, the system will NEVER work anywhere near properly.

 

G'day Always use a high pressure central coolant cap so that it does pressurize and so that the coolant tank can do any required pressure relief. Then the upper seal on the central cap does not matter.