WaIIy wrote:
I installed two PSS seals on my boat (twin 5.7's) and the fitting I put
on the manifold is quite a bit above the waterline.

I can't see, in my case, how a backflow could possibly occur.

Easily. As the manifold cools, it pulls a vacuum on the water supply to
the seals. This is one case where water will readily flow up hill (and a
little metaphysical help from Murphy's Law, no doubt).

Our engine cooling water outlet, on the injection elbow, is slightly
above the waterline. It was not connected to gland cooling water at all,
even though the piping for this connection was installed and left
hanging (maybe disconnected by the first owner). I put in a vacuum
breaker and it works 100% A-OK. The packing gland gets warms now,
whereas before it would sometimes get pretty hot.

Fair Skies
Doug King