[Too much junk]

My 04 90 hp yamaha is running low water pressure. At 5000 rpm it has about 15 lbs of pressure. At idle almost none. The pisser stream is weak at all ranges. Does this motor have a water bypass? Someone told me that it can get a grain of sand in it and wont close causing this. I would appreciate any help please. Casey
Had impeller change last year

 

[X-Shark]

The standard old rule from dealers was Each year for inshore and every 2 years for offshore. The thinking is you will suck a lot more sediment up inshore with being in the shallows.

Thermostat, Pop-it valve and "COMPLETE" water pump kit ....Not just a impeller.

 

[Too much junk]

Sorry didn't go into detail enough. This was a brand new factory lower unit installed July of 11 Thanks Casey

 

[Emerald Ghost]

Ditto with X Shark.
My Yamaha goes thru impellers / pumps twice as often as older motors.
I even resorted to having a water pressure gauge installed.
Do the housing, and not just the impeller. It is an easy job.

 

[Too much junk]

Where is the poppet valve located?

 

[Ocean Master]

It is located between the heads in the rear bottom. I'll get a pic for you.

Assuming it's a 4 stroke the pressure relief valve is located on the starboard side of the engine below the oil filter. The housing has 3 small bolts that hold the spring, grommet and plastic poppet valve.

 

[Too much junk]

It is a 90 hp 2 stroke 3 cyl in line.

 

[Ocean Master]

On the 2 stroke the poppet valve is located under the thermostat housing. It is located on top of the cylinder head. Remove the cover and it's all there ready to inspect or replace. It's very easy. Be very carefull removing the bolts. If they haven't been removed in a long time they could be corroded and easily break. If they loosen turn the bolts in and out as you remove them just to be safe. Apply marine grease to them when you put them back in.

The pressure valve or poppet valve is #39. The thermostat is #41. If the grommet for the poppet valve gets smashed or out of line it won't work causing overheating at speed.

If you are overheating at idle and absolutely know the water pump is good check or change the thermostat.

If it were me I would change the entire water pump, thermostat, and poppet valve all at the same time. Purchase all the kits or required gaskets and grommets and do it right the first time. You can also see how much corrosion there is inside the thermostat housing to give you an idea of the cooling system. The entire cooling system may need cleaning.

For reference you can go to Boats.net as I did to get the schematics for your engine and see the cost of parts.

 

[Too much junk]

Thanks everyone for the info.