[demus]

Hello,

From your drawing, where abouts do you fill the cooling system? If the only place is your expansion tank then I would suspect you have air caught somewhere.

When I redone the cooling system on my RV8 I fitted the Dax header tank (as the highest point), which filled into the bottom rad hose, then had an air bleed hose from the highest point of the engine (which happened to be the top rad hose), to the top of the header tank.

Maybe worth also making sure you have a small air bleed hole at the top of the stat. Mine seems to fill up and behave ok like that, although I don't have the manifold like yours.

Have a search around on the site as its come up several times, and I'm sure someone will be along shortly who can explain it a whole lot better than me, or know something different.

Cheers, hope it helps..