Well no-one else is offering anything so speaking as the bloke who has spent a lot of time staring into the filler of his radiator to try and work out if the head gasket was gone I'll pitch in.
Mine is a V8. If it's idling then I don't see much movement, give it a blast and the level falls and rises and yes you can tell the pump is working.
I'd say if your pump's gone and if it's a V8 it will overheat very quickly. Mine did that's for sure.
The diesels run very cool anyway.
