I decided that I needed to add a water pressure gauge to my 90hp Merc.
Being the cheap and lazy person that I am I didnt' want to buy another
gauge nor drill another hole in my dash. I recently added a GPS that
indicates speed and I never was very happy with the accuracy of my
speedometer. I determined that the speedometer just measures pressure
and it turns out that 1 psi=3mph. So after hooking my speedometer to
the water manifold tap it now reads about 30mph when running full
speed. So now I have a water pressure gauge albeit a rather large one.


Is 10 psi about right for cruising speed or is my pump worn out? Maybe
the more important pressure is down at low rpm which was about 3 or
10mph if my memory is right.

Have fun.

Don
wa5ngp

My 60 big foot uses the same pump as a 90 2 stroke. I mapped the water pressure
with a good guage, right after an extensive cooling system repair. (part of a
longer story) It tops out at about 17-18 at WOT, 14 at 4400, 10 would be about
2800-3000. At idle it will be 3-4 but when coming down from speed it will be
lower until the thermostat closes a bit.
This is at the water jacket right above the raw water inlet tube where the
fuel cooler taps off.