Water pressure issue

[BMCD]

Just had a lower unit rebuild recently, motor ran fine for a 1/2 day after rebuilding. Then it started overheating. I noticed I had good water and good psi at idle. But as soon as the bow breaks over on holeshot my water psi drops to zero water stop coming out of the engine, and overheat alarm sounds shortly after.

I would think that if I'm getting good psi at idle that the pump is good.

Any ideas?

[redline]

Did anyone change the motor mounting height??? Or perhaps install a transducer???

[BMCD]

Negative. A cav ring was added. B ut that does not explain why it did not overheat for 1/2 day.

[redline]

That's a tough one. If I could gamble.....I'd take the lower back off and be sure the water tube, water pump gaskets, and housing are not loose or blown out. When the motor is submerged, any breaches in the pump may allow adequate wpsi when at idle....as soon as the lower "breaks free" and surfaces, that's when any pump maladies will show up. Also the "carrier' beneatth the pump housing has been known to cause such issues. Don't keep running it until the problem is rectified, the compressor will be the first to go....

[EuropeanAM]

+1

You've probably got a bad gasket UNDER the impeller plate, or impeller blades are folded in different directions.

[BMCD]

Ah I was thinking the same thing a crack or hole in the pump. Its in the shop now course the mechanic said the pump looks good. I actually told him it seems like the water pump has a crack.

It kinda makes sense, I think it happened when I stopped fast (I just let of the throttle put it neutral and turned the key off while still on a plane). Because I was fixing to run thru a school of bass.

Thanks for the info.

[redline]

Your tech should be able to identify if it is the carrier {under the pump} by closely examining the impeller. It would have "burn" marks where it was / would have been compressed against the housing, around the center hub, not on the blades. The pump base must be removed for inspection.

[BMCD]

Well I was just told it is was a cracked impeller.

[EuropeanAM]

+1 That'll do it.......

[redline]

At the risk of sounding well, stupid, I haven't seen a "cracked" impeller...ever....unless it was 30 years old and dry-rotted. I'd be interested to see some pics. Burned, melted, ripped apart in whole or part, yes......cracked would be a new one for me. How 'bout you Don? Need more info.....

[EuropeanAM]

I have to agree, Bob. "Cracked" is probably being used as slang for a more accurate word of "torn". I'd love to see a picture of this impeller... especially since it was recently replaced, supposedly... or hopefully....

Of course, the "end result" is the most important thing.

About 25 years ago, in one of the earlier training classes I attended, the instructor (who was nearly 60 at the time) showed us how to "test" an impeller for a customer: "Remove it from the housing, and if the blades don't return to perfectly straight within 15 minutes, throw it in the trash." What he was actually saying (in a manner that would be understood & acceptable to our customers) is that "you don't re-use an impeller- ever". You can stick a new impeller in a housing overnight, and using the above test, you'll "throw it in the trash" almost every time.

One other thought here... if the impeller was replaced, we sometimes see "old-school" guys install them with "petroleum products" as "lubricant" (yeah... this was common practice back in the 70's). Unfortunately, the petroleum based lubricants tend to break down "neoprene" based impellers, causing early failures. If it was indeed replaced... this is a possibility, also.

The best "lubricant" for installing an impeller is "liquid dish-washing detergent". It's gone shortly after you start the motor... and it makes some "pretty bubbles" for the kids to watch.

[redline]

Even if it was torn, it would probably have to be around the center hub, as to allow the impeller to spin....if it was only one blade...the description of the problem was NOT at idle, but when it came up on plane the pressure dropped to "zero". Worn, missing or damaged blades usually rear their ugly head at low rpm......at higher rpm they might pump sufficiently.......I still think somethings not right......pics would show us the "why".........:)

[BMCD]

Impeller and water pump were not replaced on the intial rebuild, Motor is less than a year old. I was told it was cracked and the impeller was able to spin on its shaft. Apparently there is a nylon hub? on the impeller and that was cracked.

How does 1 test this scenario without driving to the lake? Remember it works at idle until you get on a plane.

Yes pictures would be nice, but I already picked up the boat and did not ask to see it.

[redline]

Thanks for the response. That was the answer I was looking for.......If it was "cracked" around the center hub, your scenario is / was entirely possible. At low engine RPM, the hub had enough tension to allow the pump to do it's job....barely. Once you put the coals to it.....the horsepower allowed the impeller hub to spin and the impeller was rendered useless.........glad it's fixed!!!!!

[EuropeanAM]

Now we're getting somewhere... and it makes sense.

This is another good reason to "never re-use an impeller".

[jigslinger]

Red and Don, you 2 walk on toilet paper, cause ya'll are the shit Man it's awesome just reading how you guy's evaluate problems...


Modified by jigslinger at 2:35 PM 7/31/2008

[esdbass]

+2 on that about Red and Don and I'm lucky enough to be a long time customer of Red's