The coolant filler cap on the front of the engine (over the water pump) is not a pressure cap on my 94. It also is leaking. I am having trouble finding the non pressure cap locally or online. Is there any reason not to use a regular vented cap, say a 20# so it doesn't open?
...Jimmy

 

Exactly. That works perfectly. It does not need to vent, just v seal to a pressure greater than the cap on the header tank. Mine leaked until i replaced with a 20#. PO had two vented 16#.

 

Agreed also.

Look up CPC (google helps here). You are looking for a CPC #2001 cap.

I use a standard "recovery" cap on the filler pipe, and the CPC recovery cap has a "huge" purpose moulded seal in that "upper" position, and that will seal the standpipe the same as the 2001, and in MY opinion seal it better than the seal arrangement of the flat 2001.

Your market may be a mongrel for the CPC caps, but good old ?bay does have them all the time.

 

From what I have read , early models had different spec caps on header tank and crossover pipe, even having chain on one cap to prevent wrong fit.
Later models according to jaguar parts list same part number for both these caps