2011 250 SHO water pressure issue?

Hi THere,

I have a 2011 yammy 250 SHO, 72 hours on it. Today I started and idle away from the dock, up to 1400rpms, and i have a nice stream of water coming out the tell tale. Everything looks normal. Now i gas to get it up on plane and as the rpm increase, the tell tale disappears. I slow down and the stream starts again. I figured out that it only happens when I start to move. I put the engine in neutral, then revved the engine to 2500, the stream flows nicely, standing still. Click it into gear and start to add gas, the stream is flowing, get it too 1500, no tell tale at all.
No Alarms, no overheating. JUST NO TELL TALE.

I limp it home at 1200 rpms (stream flowing), get it on the lift and hook a hose to the flush fitting, turn on water and everything flows nicely. I pull cowling and under cowls, inspect the thermostat hosing for leaks, and complete inspection of the block while under flush pressure nothing leaking pan inside is dry as a bone, no water contamination in the oil.

Another thing is that it has a pressure gauge, and i used to run around 13 psi at 3000 rpms, now it's running around 25 psi at the same rpm, which I've never seen before. I don't have command link plus gauges, just the standard round ones. So, this is a clue to me. Pressure has doubled, no tell tale at above 1500 only while moving.
To me there is restriction somewhere. I check all intakes for clogs, nothing. I checked all hoses and tees. I DUNNO. I told him I would post this question and see if anyone on here has got any ideas. SOMETHING HAS CHANGED TODAY. It didn't do this before. It ran fine and always had a tell tale stream.

have any of the experts on here heard of this?? Any ideas would be greatly appreciated.

I've been in contact with my marina, really helpful but they seemed stumped too. He also has another customer with this engine and doesn't have a tell at all, and showing 25 psi on the gage. He called Yamaha in Atlanta and another ace tech to discuss this, they all seem to say they think the water pump is fine, and that there is restriction somewhere for the tell.
He also said to go for a boat ride, and see if it goes into limp mode, which really hasn't happened since i drove it for a while before i noticed no stream, maybe 5 minutes. I'm really diligent about watching the tell.



Sorry for the long post, but i wanted to get it across that have debugged this a little, but I'm strummed too.

Thanks sincerely for any replies.

Capt Rob

Have you ate a water pump impeller recently? if so, when they disintegrate they can lose pieces which go up inside the engine etc and clog up stuff. Best way to flush this out is by removing the lower unit and flushing water from the engine back down thru the water pickup tube hole.

First thing I would do is remove the tale tale hose from the engine, hook up the water and let it run out from the hose connection. maybe you can flush something out so just watch and don't turn water on high.

Not sure if your engine has a pressure relief valve so you would have to look up your engine to see. If it does, it may be stuck open, which is allowing most of the water pump pressure to bypass the cylinders which in turn may cause you to loose your tale tale stream.

At low speed this valve stays shut allowing cooling water to run thru engine normally. As water pump pressure increases, this valve starts opening to allow the increased pressure to bypass the cooling which keeps more water entering the system to provide fresher water to cool engine.

The valve works like a thermostat except works on pressure not temperature.

As far as water pressure gauge changing, this could cause the difference in pressure your seeing....Also, disconnect the pressure gauge hose from both ends, blow air thru it to make sure no water is in the hose. The gauge works on pressure inside the hose from the water compressing the air inside the hose. It should never actually get water in the hose up to the gauge. The same applies to your speedometer if you have one. Only air should be inside the hose, never water.
If you have water in either hose, it means you have a loose connection allowing the air to escape from inside the hose.

trynhooker said:

Have you ate a water pump impeller recently? if so, when they disintegrate they can lose pieces which go up inside the engine etc and clog up stuff. Best way to flush this out is by removing the lower unit and flushing water from the engine back down thru the water pickup tube hole.

First thing I would do is remove the tale tale hose from the engine, hook up the water and let it run out from the hose connection. maybe you can flush something out so just watch and don't turn water on high.

Not sure if your engine has a pressure relief valve so you would have to look up your engine to see. If it does, it may be stuck open, which is allowing most of the water pump pressure to bypass the cylinders which in turn may cause you to loose your tale tale stream.

At low speed this valve stays shut allowing cooling water to run thru engine normally. As water pump pressure increases, this valve starts opening to allow the increased pressure to bypass the cooling which keeps more water entering the system to provide fresher water to cool engine.

The valve works like a thermostat except works on pressure not temperature.

As far as water pressure gauge changing, this could cause the difference in pressure your seeing....Also, disconnect the pressure gauge hose from both ends, blow air thru it to make sure no water is in the hose. The gauge works on pressure inside the hose from the water compressing the air inside the hose. It should never actually get water in the hose up to the gauge. The same applies to your speedometer if you have one. Only air should be inside the hose, never water.
If you have water in either hose, it means you have a loose connection allowing the air to escape from inside the hose.

Click to expand...

Thanks for the response. Your ideas are great and It sounds like you're spot on. I do have a little water in the water pressure line. I did disconnect it from in between the two cylinder banks. and with water pressure high squirted water 10' out of the connection. I will check for connections for leaks. Thanks for that.
These engines do have Pop off valves, I didn't realize they worked on pressure and not heat. I had a theory that the thermostat on one side of the engine was stuck shut, causing higher pressure and lower volume. Put now that I know those valves are pressure actuated, I will go right to that before changing $85 thermostats.

Thanks again for all the good debug ideas.

One question: If the pop off valve is stuck wouldn't I get an overheat alarm? Since some of the block/head weren't getting any water? This is why I was thinking it was thermostats, since they have by-passes that allow some water to flow through them.

You're the best I will run through these procedures and post back as soon as I can..

Sincerely, Rob