Does your boat have a water pressure gauge?

Does your boat have a water pressure gauge? Close-up of water pump impeller.

Assuming the answer is yes; what does the gauge really indicate and how do you interpret the readings?
Water pressure gauges are, in my opinion, the second-most important gauge on your boat. The tachometer is number one.

Water pressure gauge design is relatively common among all outboard manufacturers, but the method of how the cooling system works is developed is very different. In order to supply adequate cooling water to the powerhead, all outboard motors depend on the size of the water intakes, their position on the gearcase, and the amount of water available to flow through them up to the water pump.

Water pumps are of vane-type design, meaning the impellers have rubber fingers, or vanes. When new, the rubber is pliable and conforms well to the liner it rides in, thus creating the correct pressure and volume of flow to cool the powerhead.

Evinrude, Mercury, and Yamaha use a high-pressure/high-volume method to cool the engine. The gauges in these systems indicate pressure up to 30 psi; usually near 0 at idle to 25 at wide open throttle (WOT), with a "dump valve" to release "extra" water during high-speed operation. Suzuki uses a low-pressure/high-volume 15 psi system, the gauges will generally show around 8 to 12 psi at WOT.

Yamaha's spec for minimum water pressure at normal operating speed is 11 psi. Knowing this is important. The water pump will be at peak performance when new, so watch the gauge and learn the norm. When you see it reading consistently lower it is time for a maintenance visit. An engine overheat alarm with good pressure indicates other issues.

Water pumps are very durable; they should be flushed after every use and changed every year or 100 hours of shallow water operation. Flushing with freshwater through the intakes for five minutes with the engine running is the preferred method.

Have a great October!

Chris Mapp
Coastal Bend Marine
Port O'Connor, TX
361 983 4841