dont forget the 2 bleeder bolts

[harry3]

the 2 bleeder bolts must be undone and water forced in thru the radiator cap until it flows out both holes, or a cracked head from the steam trap thus formed can be almost guaranteed for the 6cyl engine
if these bolts havent been undone for a long time they are likely to be siezed by corrosion and will shear or break if forced with a spanner
if the bolts can be undone, coat the threads with grease
someone has suggested removing the rubber hose from the front of the intake manifold and forcing in water with a plastic soft drink bottle as an alternative

confusingly, the same engine in the nissan skyline also has bleeder bolts and the top of the radiator also seems lower that the highest water passage, but the skyline isnt known for cracked heads??
as a footnote, a worrying water loss on my VL was eventually traced to a defective radiator cap!! it looked fairly new and the rubber parts seemed undamaged

[bangers]

i had the same trouble with my radiator cap too. put a new one on and the pressure in the system then blew the water pump which must have been on its last legs. and it was me that said about the rubber hose, i was shown that by a couple of mechanics.