Raw Water Impeller pump has trouble priming

[BuFootin]

Anyone ever experience a problem with the impeller pump not priming? This winter I installed the Y-fitting in line with the raw water hose before the impeller pump (better heat from the heater at low speeds). Twice now when I dropped the boat in the water the impeller pump did not pump water until I increased the engine RMP's above idle. The outside of the impeller housing warms up from friction, but then after increasing RPM's the pump begins moving water and the housing cools off like I'd expect. Brand new impeller installed this spring. Pulled impeller today and inspected it and no visible signs of wear or damage. Removed all hoses on both sides of the transmission cooler to check for blockage. Found nothing.

Any suggestions?

[VinRLX]

Is the boat on a hoist or trailer? This happened to me once, with a completely empty block and heater core, when I lowered the boat enough to start it but not all the way down into the water.

Is your raw water through-hull valve all the way open? I would pull the hose at the impeller and run a garden hose through it, against the normal flow, to see how easily it runs out the pick-up on the bottom of the boat.

[skier92]

There have been several posts that question why the Y-fitting is installed after the raw water pump, by the factory, when it gives increased heat when intstalled before pump. My belief is that it's installed after to prevent just the problem you are experiencing. The raw water pump creates low pressure on the on the pickup side of the pump. Atmospheric pressure on the water surface (that the the boat is sitting on) forces water into the low pressure area created by the pump. Putting the Y on the pickup side reduces the ability of the pump to create the required low pressure area in the pickup hose.

[scfdfireman]

Check for small air leaks on all connections on the intake side of the impeller pump. Also check the pumps housing for scoring or heat spots which can reduce its ability to draw in and pump out water. The pump is just a small positive displacement pump, and as long as the piping before the pump is air tight it will draw a vacuum on the space and draw in water from the inlet. The only delay that the pump will see is the time that it takes to draw a vacuum on the added area on the suction side of the pump. I can't see that the area of a simple "Y" fitting would cause this delay that you're describing.

[martinarcher]

I had the same deal with our boat this spring when i fired it up with the fake-a-lake. The block was empty, but after a couple minutes, no water out the exhaust so I shut her down. I pulled the intake hose to the pump and there was no water and still trace of antifreeze so i knew it wasn't drawing water. I forced the fake-a-lake tighter on the bottom of the boat and forced water into the pump with the hose pressure and it primed OK. This is our first spring with the Bu so i figured it was normal with a dry pump after storing for the winter. Should I look into changing the impeller and intake hose?

[skier92]

Here's a simple test to see if the problem is from the Y fitting being installed on the inlet side of the raw water pump. Next time out, prior to starting motor, crimp the hose to the heater, right next to Y fitting (hose clamp pliers or two bolts & vise grips) Start engine. If pump primes in normal period of time at idle, Y fitting location is the reason for problem. In addition to the theory previously posted, problem was not present last year prior to Y fitting install. Simple physics dictate that it is easier for the pump to draw water out of the engine (through the heater loop) fefore enough vacuum is reached to acheive prime in water pickup.

[the_dude]

I have this same exact problem each time I drop my boat in the water. I have no Y fitting and no air leaks. I do however, remove the V-drive to raw water hose to flush the boat after each outing which causes quite a bit of air to get in there for the next time.

[VinRLX]

Simple physics dictate that it is easier for the pump to draw water out of the engine (through the heater loop) fefore enough vacuum is reached to acheive prime in water pickup.

I believe your are correct in your earlier post--that Malibu does not install the Y prior to the impeller because of the possibilityof not priming. However, there are many boats out there with the Y placed prior to the impeller. If your example above were completely correct, my impeller would never prime.

[BuFootin]

Thanks for the all the replies. Boat is always on a trailer, not a hoist. I dip the boat all the way in before starting on the ramp. Went out yesterday fired it up and all ok. Although, I rev'd the engine after starting. Got a great day of skiing & footing in anyway.

The 2 times the impeller pump did not prime the block was full of water. So I don't think this is the source of the problem. Common sense would say it has something to do with the Y fitting before the impeller since last several years...no problems.....install Y fitting....pump won't prime.

I actually thought of pinching off the small heater line connected to the Y fitting. I'll try that and see what I discover.

[VinRLX]

Check for small air leaks on all connections on the intake side of the impeller pump.

BuFootin--good point made above, particularly because you just added the Y fitting.

[BuFootin]

Check for small air leaks on all connections on the intake side of the impeller pump.

BuFootin--good point made above, particularly because you just added the Y fitting.

Thanks, will for sure check for tight connections throughout

[scfdfireman]

Today, I just added a "T" fitting to my Bu for a garden hose connection and it didn't effect the raw water pump performance at all. One thing that you may want to try is to locate any leaks (that could effect the pumps ability to prime). To do this, hook up a garden hose to your fitting, close the ball valve at the boat bottom and turn on the water supply. Run the motor for 10-15 minutes and if you have leaks / drips on the pump face plate gasket, at the rear shaft seal or hose connections there's your problem. Just a note, I have low hours on our Bu, and everything was dry during the test...