Water Pressre vs. Temp Gauge?

[zenoahphobic]

Ideally you want a water flow indicator, but does such a thing exist? The problem often with an outboard motor there is not a point on the engine or to get to if there is a point where all the water that has passed through the engine to get "readings" from.
In a car that is easy (eg all water goes via one hose through a radiator) but is never done as temp guage seems to be totally adequate in determining whether the cooling system is functioning, as well as engine malfunction that is also harder to determine from an outboards cooling system.