[nipper]

In day's gone by several European Truck Manufactures used to fit Radiators which had a one way valve fitted into the base of the radiator to allow the cooling system to be filled from the bottom thus pushing any air out through the top as the system filled.
Wether it would be possible to say modify a rad drain plug or similar to be able to fill the P38 system in a similar way I don't know.

Might not even work or be worth the effort as I guess you would have to have some form of pump to force the water/antifreeze in under pressure as gravity alone may not be sufficient.

Not suggesting anybody does this or that it practical to do taking into account how often you actualy refill the cooling system. Just thinking out loud of way's it may be possible to fill the system to avoid potential air locks.

Cheers

That sounds like a good idea. If an on/off valve was fitted where the drain plug goes and a container of water/antifreeze was placed above the top of the radiator would that not fill the system by gravity?