Scottoiler

[nick crisp]

On prime it should just flow through without the engine running. That would be a good test as to whether it's vacuum related or something else.
Have you checked the breather tube out of the top is clear? It need that to replace the air in the unit in order to let the oil flow down

Ok, I removed the breather tube, and can blow through it, so that's clear. I have had it set to prime for a few minutes now, and nothing coming out. All the pipes look in good condition, no kinks, holes or anything else that I can see. And as said, I know it was working before I ran the system dry  :\

But when you fit a new one, that's empty to start with, then you prime it, and all should be ok. So what's different here?