Bravo II - do I have a sea water blockage?

[frank2644]

Starting my engine on rabbit ears after winter storage I noticed that no sea water was flowing.

After poking around a little I pulled the outlet hose off the sea water pump and I saw no water flow out of the pump. I then pulled the input hose off of the pump and also saw no water flow into the pump!

How can there be no flow into the pump? The path from the rabbit ears to the inlet of the sea water pump is just hoses or BII water passages, I think. I decided to back-flow the water by putting water into the pump inlet hose and sure enough water flowed very freely out of the Bravo II water inlet slots. I repeated this test several times and got the same results. That is, no forward flow but plenty of backward flow.

So there you have my problem, why doesn't water flow from the rabbit ears through the Bravo II input slots and into the sea water pump and yet flow very freely in the other backward direction? Is this normal somehow? Is it possible the water must be sucked into the pump and that just pressurizing water with rabbit ears is not good enough?

BTW, I took the sea water pump apart and the impeller blades are busted up pretty good. Okay, it's been at least two years since the impeller was changed so I guess a broken impeller should not be a surprise. But is this just a normal impeller failure due to excessive use or did the pump run dry causing the impeller failure?

Any suggestions, ideas, thoughts? All feedback is appreciated, I'm stumped.

 

[Lazy Daze]

Water should not flow easily (in either direction) past the sea water pump. Those impeller blades make a very tight fit. Seeing as you took a look at your impeller, I think you figured out the reason why you weren't getting water, huh? Yes, you are correct - the impeller sucks the water up to the circ pump, which then distributes it through the engine.

Why are the blades so bad? Hard to say - sand, silt from shallow running; running the pump dry... could be a number of things. Once you get it all back together, keep a close look on your temp gauge - especially for the first few hours.

 

[Quint4]

"impeller blades are busted up pretty good"...I think that is your answer....the pump is unable to prime itself because of impeller failure. Replace it and give it a good shot of dish soap for lube for initial dry start up.

 

[AKBASSKING]

Hey Frank,

Running the pump dry will tear the impeller up in about 45 seconds. I just fixed a similar issue on my Stbd engine this weekend. The impeller was torn up and the pump was missing parts such the back plate.

I rebuild the pump. Kit cost me about $80.00 for the kit and a little blood. The most important thing is to make sure you install the impeller properly (inserted into the pump body in the same direction as the engine turns).

I installed a "T" on my water pickup hose, so I can close my seacock and have positive flow to my engine.

 

[Henry Boyd]

Frank,

The Bravos are very temperamental on their water pickup. All the comments about changing out the impeller in the pump are correct, but you still might have problems. I ended up having a through hull and strainer installed. Interesting enough Mercury has a recommended conversion plan for this.

Henry

 

[frank2644]

Thanks everyone for the comments.

In case my original post wasn't clear let me describe the blockage problem again: With the sea water pump inlet hose disconnected from the pump there is no water flow from the rabbit ears. It seems like there is a blockage in the out drive or the hose. However, if I reverse the direction by putting a garden hose into the pump inlet hose (not the pump, the hose) the water flows freely out of the outdrive water inlet slots. So somehow the blockage is only in the normal water flow direction. I can't imagine what could block the water flow in one direction, but not the other direction, but that's what is happening.

At this point I intend to rebuild the sea water pump and see if it will pump the water. If it does, I'll measure the flow as explained in the engine manual. If it meets that flow specification I'll assume all is working properly. If it does not meet the spec then I guess the blockage I described above is real and I'll have to take off the stern drive and inspect it.

If anybody has any other ideas or insight, I'm all ears.

 

[Nehalennia]

With it disconnected from the pump and the impeller not able to suck the water up the leg into the pump(with water flow and Ear Muffs on) you won't get the water to reach up that high.

 

[Lazy Daze]

Agree with above. The water coming out of the hose just doesn't have enough force to over power the rise that it needs to in order to come out where you are expecting it. You could try re-routing the inlet hose to a lower position, if you felt inclined. Still, water may or may not come out. Don't over think this one or you'll end up... :smt021

 

[Jimmy Buoy]

I used to have a 268 SD with a 7.4 & Bravo I. What I did was to disconnect the water supply hose from the drive housing inside the engine compartment. It would stay vertical so I'd put the garden hose (without any fittings on the end) down into the cooling hose and turn the water on. It would of course overflow into the bilge, but once I starte the engine is sucked more water than the garden hose could supply even at idle.

If your water supply hose is accesible as mine it was a better/faster water feed for the impeller on the engine - so less likely to overheat the impeller prior to water reaching it.

 

[frank2644]

Guys, thanks for the input.

As far as the hose not being able to "overpower the rise" that's hard to believe. The rise is only about 7 feet. Also I can raise the hose nozzle much higher than that and the water still flows. I can remember bringing my hose onto my roof to wash out the gutters and there was plenty of water flow.

Anyway, as one reply suggested I may be "over thinking" this problem.

Thanks, again.

Frank

 

[Lazy Daze]

Guys, thanks for the input.

As far as the hose not being able to "overpower the rise" that's hard to believe. The rise is only about 7 feet.

But, the column of water that you're raising doesn't stay the same diameter as your hose. The column eventually gets bigger as it goes through the drive and into the hose. Which also means it gets much heavier.

 

[Nehalennia]

Guys, thanks for the input.

As far as the hose not being able to "overpower the rise" that's hard to believe. The rise is only about 7 feet. Also I can raise the hose nozzle much higher than that and the water still flows. I can remember bringing my hose onto my roof to wash out the gutters and there was plenty of water flow.

Anyway, as one reply suggested I may be "over thinking" this problem.

Thanks, again.

Frank

But, the column of water that you're raising doesn't stay the same diameter as your hose. The column eventually gets bigger as it goes through the drive and into the hose. Which also means it gets much heavier.

+ I'm sure the water is leaking out of the muffs while you have it hooked up. Put a new pump and impeller in, hook it up and try again. The Impeller sucks the water up through the leg and into the pump.

 

[frank2644]

I did put hand pressure against the muffs to try and minimize leakage, but some water was still squirting out in streams a couple of feet long (that suggests pressure was building).

Relative to the column of water getting bigger in the out drive and, therefore, the water weight was heavier than a simple pipe, I don't think that's valid. The best example I can think of is the typical house water heater. Water is piped into the bottom of the water heater where the flame is and still manages to come out the top despite the tank being very big. Furthermore it continues to travel a couple of floors higher without aid. I also believe that these water heaters can be installed on the 2nd floor.

In any case, I picked up the rebuilding kit today and will likely have it installed this weekend. I'll post the results.

Thanks again for the replies.
Frank

 

[Nehalennia]

Well anyway, good luck.

 

[Lazy Daze]

The best example I can think of is the typical house water heater. Water is piped into the bottom of the water heater where the flame is and still manages to come out the top despite the tank being very big. Furthermore it continues to travel a couple of floors higher without aid. I also believe that these water heaters can be installed on the 2nd floor.

But the water coming into a water heater is actually entering from the top. That means it's not actually pushing the water up, instead the water is simply trying to reach it's own level. As far as it traveling up to the 2nd floor, sure, but it's staying within it's 1/2" pipe at constant pressure.

When the water enters your drive, the pressure is dropping off rapidly.

If you take your garden hose (as you said) up to your roof, the water is staying within the confines of the hose. Try this: While standing on the ground, take the nozzle off your hose and hold the hose end vertically. Does that column of water (which is now exiting the hose) still make it to the second floor?

However, I do see where you're coming from. If you can get those muffs to seal really well (water will take the path of least resistance), and water still does not come out the inlet hose (at the pump), yes there must be a blockage. It just doesn't make sense that water would flow in the reverse direction through the inlet hose, but not the way it normally goes.

You are positive you took the correct hose off and gave it ample time to try and flow?

 

[frank2644]

But the water coming into a water heater is actually entering from the top. That means it's not actually pushing the water up, instead the water is simply trying to reach it's own level. As far as it traveling up to the 2nd floor, sure, but it's staying within it's 1/2" pipe at constant pressure.

When the water enters your drive, the pressure is dropping off rapidly.

If you take your garden hose (as you said) up to your roof, the water is staying within the confines of the hose. Try this: While standing on the ground, take the nozzle off your hose and hold the hose end vertically. Does that column of water (which is now exiting the hose) still make it to the second floor?

However, I do see where you're coming from. If you can get those muffs to seal really well (water will take the path of least resistance), and water still does not come out the inlet hose (at the pump), yes there must be a blockage. It just doesn't make sense that water would flow in the reverse direction through the inlet hose, but not the way it normally goes.

You are positive you took the correct hose off and gave it ample time to try and flow?

Although water entry fittings are on the top of a water heater internally there is a pipe directing the water to the bottom where the heat source is. Although I guess that complicates the analysis and maybe the analogy to my problem is not that good.

Relative to your "take the nozzle off the hose" question, obviously the column of water will not reach the second floor. But I don't see that proving anything.

Yes, I'm positive I took the correct hose off and gave it ample time. Although maybe my rabbit ear seal was not that good. I did try to seal the ears to the I/O but there still was significant leakage. Unless I have some weird kind of one-way blockage I can't see any other explanation.

I'll post what happens after I rebuild the pump.

Thanks
Frank

 

[Lazy Daze]

Yes, I'm positive I took the correct hose off and gave it ample time. Although maybe my rabbit ear seal was not that good. I did try to seal the ears to the I/O but there still was significant leakage. Unless I have some weird kind of one-way blockage I can't see any other explanation.

I'll post what happens after I rebuild the pump.

Thanks
Frank

You definitely got my gears turning on this one! I do agree with you that it should come out, eventually, although I think the key is the good muff seal. But I just can't fathom what could be stopping it, you know? Maybe there's something foreign in there acting as a one-way check valve, but what? I'm at a loss. Unless you figure this one out for us, I'm gonna have to take my own hose off!



Stumped,
Dennis

 

[frank2644]

You definitely got my gears turning on this one! I do agree with you that it should come out, eventually, although I think the key is the good muff seal. But I just can't fathom what could be stopping it, you know? Maybe there's something foreign in there acting as a one-way check valve, but what? I'm at a loss. Unless you figure this one out for us, I'm gonna have to take my own hose off!



Stumped,
Dennis

I did install the out drive myself for the first time. I guess I could have done something wrong or left a rag inside. I don't think so, but I suppose anything is possible.

Frank

 

[Lazy Daze]

I did install the out drive myself for the first time. I guess I could have done something wrong or left a rag inside. I don't think so, but I suppose anything is possible.

Frank

When you figure it out, please be sure to let me know. Good luck - I hope it's something simple. :smt001

Dennis

 

[Woody]

Posted by Lazy Daze...Try this: While standing on the ground, take the nozzle off your hose and hold the hose end vertically. Does that column of water (which is now exiting the hose) still make it to the second floor? Actually water would make it to the second floor again, once it fills up enough of the world.

The hoses and water flow are basically horizontal between the transom and water pump. The water pickups/muff are a couple feet lower than this so you lose a couple psi due to increased head. Set all the hot water heater and garden hose stuff to the side. If you muffs weren't leaking like a sieve you should get water flow from the disconnected inlet hose unless there is an obstruction. Other than anything you may have done in the process of r/r of the drive the only thing I can wonder about is the condition on the hose itself. How does it look? Is it possible there is a flap of deteriorated hose that blocks flow from one direction?