Re: '72 merc 1150 water pressure reading
I don't have the OEM shop manual for your particular motor so I can't look up the specs. However, it is a good idea anyway to replace the impeller at the same time as installing a water pressure gauge. This allows you to determine the "normal" pressure readings for the motor at various RPMs. Once you know this, you can monitor the guage to see if the readings drop below "normal" , indicating that the impeller is starting to fail.