Check the expansion tank pressure cap as well.

Are there any specific conditions under which the symptoms occur? Does it happen when both hot and cold? How do you determine all electrical power has been lost? No lights on instrument cluster, failure to crank etc?

Bear in mind the current wiring colour may bear no relation to the wiring diagram if the PO has spliced new wires in or replaced sections of the wiring loom. Worked on a SIIa recently where the last 6" of each wire to the instrument cluster had been replaced with random pieces of domestic cable...

Hello all, new member joining from Northampton; currently own a D3 2.7 TDV6 and P38 4.6 Thor. I specialise in electrical fault diagnosis and engine performance diagnostics.

Coil over plug on the 4.2 SC