A Mercury outboard water pump is a engine cooling system. A outboard water pump is what blows steam through to get the car cool,
it has a shaft that go in the motor that moves the boat =-Þ
the pump can be an impeller type driven by a electric motor activated by a float switch, pressure switch depending on the configuration.
What are you consider "too low." The pump will run if it's turned on, usually dry until the high limit temp on the motor kicks out. As long as there is water supply, there is no reason the pump wouldn't work. If the water level is below the skimmer but the pump can draw adequate water from the main drains it will still work.
The link I have provided below this answer will give you the best description of CDI.
A water pump works by using a motor to create suction that draws water into the pump. The pump then uses pressure to push the water through pipes or hoses to another location. This process allows the water to be moved from one place to another efficiently.
It may be that the pump has quit. Have someone get in the vehicle and hit the washer and listen at the bottle for the pump motor to work. If nothing, replace pump motor.
Instead of hydraulic pumps, hydraulic gear motor does not work. Hydraulic pump hydraulic motor blade is used instead.
you pump the water out until it comes out
In order to maintain your outboard motor correctly I would suggest using an online checklist when servicing your motor. Here is a website that has some excellent check lists to work by: http://www.discoverboating.com/owning/maintenance/outboard.aspx. Most importantly the regular maintenance revolves around checking the fuel line for cracks, rust, general damage or if water has gotten into it.
The bad thing is you have to get in a really tight place. The motor is turned sideways as you know and you have to get to the water pumps an the side next to the passenger fender. You actually have to hoist the motor up to get the pump out. Dont take the motor all the way out just take the mounts loose and lift it at an angle and get to work. If you remove the passenger side tire, then remove the plastic side splash guard you can access many of the bolts for the water pump from there.
An impeller in a pump is the part that the motor spins that actually does the work of moving the water. Due to it's design when it spins it creates a vacuum that pulls the water in the middle of an opening on the front of the impeller and throws it to the outside where it is then channeled to the output of the pump.