2003 mercury 150

[gss036]

Blue Heron, you are correct on your description, except, all of the engines do not produce 23-25 # pressure. My 2.4L Merc 89 200 HP produces 12 PSI at full throttle as per the OEM Manual. I think it depends on which engine you have. If it does not have a water pressure guage installed you should do one right away. Then you know for sure water is circulating.