Help me understand the impeller "path"

[RussGW270]

I need some insight here.

Let's assume, for argument's sake, the impellers on the engines I have are fine and working.

Let's also assume I had them working (which I did) just prior to swapping oil, oil filters, gas filter, plugs.

Let's also assume, since I have tested this and it is true, that I can get AIR through the pee-hole and down to the lower unit with an air compressor.

The likelihood of both engines no longer peeing out the pee-hole with those assumptions is pretty hard to explain. Is it likely? No, Possible? yes. Both engines at the same time, after just having been rebuilt and working prior to my "fixes"?

That being said. The shaft turns, the impeller turns, it pushes water up the engine.

What else could make the water not come out?

Thermostats?

If one thermostat is working (since it has 2).... wouldn't it still, possibly, pass water through, even a drip?

What else might also affect the water flow?

I just started the second engine, exact same issue as the first. I find it very hard to believe that all 4 Thermostats stopped working at the same time. Not ruling it out. Still replacing them, but.... still, something else is at play here.

The following were all replaced on both engines:

1 - All three new batteries
2 - Both fuel Separators.
3 - All plugs
4 - Gas filter
5 - Oil and Oil filter
6 - Gaskets for all the above.
7 - Gasket for oil drain


That's it. Everything else was working prior to all of this. I also disconnected the electrical from the batteries to the heads via the cable on the port side of the engine, to do the compression tests.

Drawing a blank here.

Oh, I have the cowling off of each Starboard side of each engine.

See the attached picture. The tub is completely full and the 2nd picture shows the ports on the engine and where the water line reaches.



Russ

 

[wspitler]

In your picture the impeller inside the white housing is not in the water. It will try to suck up water, but it only has air to prime itself with. In a perfect world it may prime, but I've found it much easier and better on the rubber impeller to get it submerged before starting the engine. Once primed it will easily stay primed and suck water out of the lower unit pickups. Attaching a hose to the flush fitting may allow it to prime itself and them you can probably turn off the hose and allow it to suck water out of the tub, but maybe not. Underway, the pickup ports are designed to provide a small amount of water pressure up to the impeller so the anti-ventilation plate, where your red line is, may be flush with the surface of the water. Try a hose to prime the pump, but submerge the pump and I'll bet you will be fine. You could also use dual sided muffs which work well also.

 

[RussGW270]

ok... yea, that was where my mind is going. This is a question of.. the pump is higher than the water line.. so.. 24" is not enough without help. I need to get it deeper....

So, back to trying to find a dang 30" tall by 2' wide x 30" long flush tank....

Or, like you said.. hook up the hose and fill it with water..

Thanks

Russ

 

[wspitler]

Hook up a hose to the flush fitting and leave your engine submerged as much as you can with your current tub. Turn the hose on full blast until you see water coming out into the tub or peeing. Then start and run the engine at idle and let it get well primed. The slowly turn off the hose and see it the impeller stays primed. I'm guessing that should work.

 

[RussGW270]

Ok, took a bit of pressure but it is flowing now. Temps are not high on the output.

Flow is not strong at idle, but ramps up as I give it throttle.

the water line is barely above the water pump, so a slightly taller tub may help.
Should not be this difficult. My Mercs never had issues like this heh...if the vents were down, it peed.

But, this gets me where I need to be.

Still have new thermostats and water pump kits inc.

Thanks,

Russ

 

[wspitler]

One of my F250s has a very weak pee stream and actually runs cooler than the other, which has a strong stream, even at idle. Most Yamaha techs will tell you that you can run the engines at lower RPMs on the flush fitting. I wouldn't run high power in the tub since a lot of exhaust will fill the tub and cause an overheat.

 

[RussGW270]

Yea, just ran for a second or two to see the water change with the revs. I am letting it idle for thirty then hooking the other engine up and doing the same. Once the tub epties. After that cools, will re-test compression.

R

 

[Sparkdog118]

One of my F250s has a very weak pee stream and actually runs cooler than the other, which has a strong stream, even at idle. Most Yamaha techs will tell you that you can run the engines at lower RPMs on the flush fitting. I wouldn't run high power in the tub since a lot of exhaust will fill the tub and cause an overheat.

That sounds like you may have a thermostat stuck open or a weak pressure release valve. When the therm is open, the p stream pressure goes down and so does the running temp. P stream is like a pinhole in the middle of a garden hose and the thermostat and poppet valve is like a spray nozzle. When the spray nozzle is closed, the pinhole has lots of pressure. When the nosy is open, pressure goes down at the pinhole.

 

[RussGW270]

Second engine is running fine now. It also has a stronger stream than the other. I raised the water level by an inch, who knows. Running it about 30 minutes or till it is no longer cool to the stream then will let it cool off and re-test compression.

R

 

[Sparkdog118]

The slot on the right side between the sealer ring is the prime passage way. If it was blocked with sealer when the mechanic installed the o ring there, may stop the prime process.