Re: Water is not beeing sucked up... 03 Mercruiser 350
Quadruple confirmation of raw water pump needing attention. In trying to read between the lines I am assuming that this boat is something you bought used maybe this year or last year (you say you are new to the boating scene)? Do you do your own work on it or do you take it to a shop? If you do your own work, and this is a new-to-you vessel, and you don't have detailed maintenance records, then my friend you must do the following:
Replace every rubber part; hoses, belts, impellers, etc. on both the engine and the drive. New bellows on the drive. Grease the ujoint.
New cap, rotor, wires and plugs.
New water circulating pump. New thermostat.
Change the oil and filter, power steering fluid if fitted, and coolant if closed cooling. New fuel filter/separator.
Inspect motor mounts, tighten as needed, grease up exposed threads on adjusters.
Spot treat and touch up paint any rusty areas
Check, clean and re tighten all electrical connections, pay attention to the grounds and hot feeds especially.
This will get you back to home plate as far as the engine's health and well being are concerned and give you a starting point for all your future maintenance. Keep records. If it is a 2003 model boat, it is well past due for all of this.