"Homer2911" wrote in message
oups.com...
If I push my engine hard for any length of time, as on the upper
reaches of the Llangollen in the tunnels, it develops an air lock in
the top of the skin tank and overheats.

Might this be a sign of water pump trouble, or is it summat else?

Think logically, how is the air getting into the system? Head gasket is the
most likely, get it tested.

mrcheerful