Hi All again.

Just a final update ... (I hope)

After some hunting around, finally tracked down a radiator bleed screw.

Had the bleed screw in for about a week now. Did numerous long and short runs. Everything (temp & thermostat operation) looks fine so far (touch wood). Even the cooling fan kicked in.

The good thing is no more injector warning lights ! ... at least for the time being.

Once again, thanks to everyone for offering the great advice.