See full version: Does your boat have a water pressure gauge
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. more
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. [links]
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.
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. [links]
We have a solution for this with the change of an impeller. We have made these modifications for years and have always had great results. This modification takes the cavitation out of the pump and allows you to never lose prime, also significantly boosting water pressure. more
We can also modify the impeller and ship to you. [links]
Any of you guys having issues with low water pressure when on plane or jacked up? We see this a lot with cat and tunnel boats losing prime/ pressure with Yamaha TRP lower units and Yamaha 4-strokes 115-300 hp.
Call in and ask for Dillon for further details 281-559-BOAT (2628) [links]
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Re: Outboard water pressure gauge questions here
I recently had one installed in my '99 Merc 250 EFI and at idle it shows almost no pressure and only goes up to about 7psi at cruising RPM, around 4600 RPM. I asked the guy who installed it and he said that it's fine and that once the poppet valve opens up it dumps all of the water out of the head so the pressure is low. I use the water pressure gauge to monitor pressure as there are a lot of weeds by me and every now and then you look down and see the pressure drop and you can slow down and clear them off before the engine heats up.
Water pressure gauges could indicate weeds built up on pick up or plastic that blocks the pick up and the pressure drops. Pressure drops are an earlier indicator of overheating then a temperature gauge. here
Drill and tap into the water jacket more
There are temperature sensors that attach with a Z bracket so they contact the head of the motor. more