2016 Yamaha 250 SHO cooling issues

[Fraghouse]

New to this forum, having some cooling issues with my 2016 Yamaha 250 SHO 4 stroke. Just bought the boat a few weeks ago has 88 hours on it, took it out and set off the temp alarm, only around 6 psi at WOT so I decided to have it serviced, mechanic said it was more than likely the impeller and that he ran it and all was good after the impeller change. Took it out and pressure was a tad better but still only 10psi at WOT. I have trust issues so I decided to replace the impeller myself to make sure it was actually changed, did the entire rebuild kit and also replaced the housing, took it out and seemed a tad better but still 11psi at WOT. Decided to descale the motor used rydlyme 3.5 hour flush and also replaced the thermostats. Got a pretty good amount of scale out and motor looks very clean now in the thermostat housing so I think it did a good job. Took it out and the tell tale was a lot better but psi at WOT only hits 12 or so and will drop, goes up and down. My next step is replacing the water pressure gauge and sending line but I have a gut feeling this won’t fix it. My question is where are the common blockage areas in the motor? I’m thinking I might have some pieces of wood or rubber causing a blockage at WOT. Iv been told by multiple sources that I should be around 20psi at WOT so that’s my goal. Motor has low hours and was only in salt 2 times. This is driving me insane lol I’v been told to check the fuel cooler area for clogs but I want to hear what some of you guys think before I start getting crazy working on it. I really don’t want to take it back into the shop and get hit with another $600 and I don’t mind working on it myself I just need a little guidance, this is my first outboard and my first Yamaha outboard. I really want this thing in tip top condition so I can take my family to the bay in confidence. Thank you for the help my friends.

[boscoe99]

Are you having a cooling issue or a low water pressure issue? Has the warning horn sounded? Has the motor gone into RPM reduction mode?

[boscoe99]

11 psi at WOT is the stated minimum. But it is not absolute. If the warning horn is not sounding there is no problem. Many Yams cool just fine with very low water pressure.

[Fraghouse]

Are you having a cooling issue or a low water pressure issue? Has the warning horn sounded? Has the motor gone into RPM reduction mode?

The warning buzzer was going off before the impeller change but has not the last few trips but I haven’t trimmed the motor up at all for speed because of the low pressure.

[Fraghouse]

11 psi at WOT is the stated minimum. But it is not absolute. If the warning horn is not sounding there is no problem. Many Yams cool just fine with very low water pressure.

So you think it’s fine? It makes me nervous that it’s at the minimum pressure. It also bounces some so at WOT it might be at 12psi and then drop to under 10 then back up. Kinda weird to me that’s why I was thinking there might be some debris that the rydlyme wouldn’t dissolve stuck somewhere.

[99yam40]

PRV opens at some pressure to relive higher pressure, but I have no idea what that pressure is.
maybe if that spring gets week it could cause lower high RPM pressure.
Just my thoughts

[boscoe99]

Inspect the plastic water inlet grates to make sure they are flush with the cavity into which they seat.

[boscoe99]

No PRV on that model.

[99yam40]

No PRV on that model.

now why would Yamaha build a 250 with no PRV.
just to confuse people?

[boscoe99]

now why would Yamaha build a 250 with no PRV.
just to confuse people?

Not sure of the real reason. It definitely confuses folks. They go looking for something that does not exist.

[99yam40]

Kind of strange that they decided to install the PRV in the large outboard to control water pressure, but this show does not need it now.
maybe too many problems from the PRV over the years

[Fraghouse]

No PRV on that model.

That’s hilarious, Iv spent probably 2 hours searching online for that thing, was about to drive to the storage and find it on the motor. LOL no wonder I couldn’t find it in the diagrams

[Fraghouse]

Not sure of the real reason. It definitely confuses folks. They go looking for something that does not exist.

Awesome diagram!!!

[Fraghouse]

So let’s say the water pressure is good around the cylinders, thermostats and all that but there was some debris in the fuel cooler, or rectifier regulator… would it affect the pressure reading to the gauge or no? Looking at the diagram the cooling system seems a lot more simple than I imagined. I just can’t get over the low pressure issue. I would really like to see it higher.

[boscoe99]

So let’s say the water pressure is good around the cylinders, thermostats and all that but there was some debris in the fuel cooler, or rectifier regulator… would it affect the pressure reading to the gauge or no? Looking at the diagram the cooling system seems a lot more simple than I imagined. I just can’t get over the low pressure issue. I would really like to see it higher.

From where on the motor are you getting your water pressure?

Folks want higher oil pressure and higher water pressure and lower temperature.

Drives twin and triple drivers crazy when each motor has a different value. To the tenth of a degree.

Ah for the good ole days of a needle about at the 12 O'clock position on the dial.