I recently purchased a 2000 Ranger R81VS with a Mercury 150 EFI on it. This is my first real bass boat, i previously had a tracker with a 40 merc. What is the water pressure guage for? Also, would anyone know what size gas tank i have. I cant find it anywhere in my manuals.

It's always good to know you have good water pressure. The guage becomes especially valuable if you have a jack plate on your boat, depending on the setup a jack plate could run the motor water pickup out of the water resulting in no water and an overheated motor.

The water pressure guage is for the engine, a water pump impeller picks up water supplied through openings at the bottom of the trans above the prop and sends it to the engine block to keep the engine cool.

The pressure guage is there to supply information to you as a visual point of reference to let you know if there is a malfunction in the system or if it is operating correctly.

The pressure should read roughly around 40 psi, not all guages are the same and some will differ greatly but if it shows good pressure and the water return port, or what we affectionately refer to as the "pee stream", seems to be operating correctly then you should have no issues.

It is common to see this guage fluxuate as you increase in RPM's and decrease, as much as 10 to 15 psi, the lowest you want to see this pressure is 15 psi, any less than that could mean you have an impeller issue or a restriction.

Hope that helps.

Good luck and be safe !!!

thanks for the responses. I know all about the water cooling the motor and such, i just didnt know what PSI its supposed to be at and such.

A 150 mercury will idle at 2-5psi and at wide open throttle be 20-25 psi.