Raw water pump

rasbury

Well...have been working on some things and in the process replaced the impeller that desentagrated...got it all back together and the pump does not seem to be pulling water and I don't understand why. Now I have a thru hull water pick up as well as a foot pick up that goes into a strainer and then the pump. I opened up the strainer and there is water in it, not full but up over the inlet to the pump. Over the years it seems I have had issue running this set up on muffs and generally avoid it. I pulled the end caps off the heat exchanger and don't see anything in there. I have what would seem to be the hard round edges of the old impeller and would assume the smaller pieces would make it through the system...
The only thing I can think I'd I'm pulling air somewhere. How much of an air leak would cause it not to draw? Like the thru hull...I have it closed but maybe it's not sealing? The strainer seal?If I take it to the ramp and just let it run, if there is no water in the system would it read on the temp gage or where is that sensor at? I suppose it is reading coolant...any way the system can get locked and just won't pump?

aero3113

It’s possible that when you sanded the back plate it’s now too thin and not making a seal with the backside of the impeller. I’m pretty sure there needs to be tight tolerances on the back plate.

rasbury

Areo- think about that- you have through holes that the bolts go through pulling the back plate to the seal- it would not matter how thick or thin that back plate is- ?

aero3113

I can’t remember what but I’m 99% sure that there’s something in the pump where tolerances matter. Could it be that the impeller vanes were installed backwards? This recently happened to @YYZRC once he reset the impeller all was good.

YYZRC

@aero3113 the tolerances matter at the backing plate which is likely why Merc redesigned and replaced the all-brass backing plate with a composite backing with insert (also cost savings I’m sure). 

I believe the impeller is relatively self priming in that it is at/below the waterline. My 330 was equipped with 350 Mag Horizons with the dual pickup arrangement. I never ran it on muffs except to winterize it. 

rasbury

Thanks guys...my point about the backing plate is I don't think it matters if it is 1" thick or 1/4 "- the bolts pull the backing plate towards the seal and the pump. Also, I did make sure it was installed with the rotation of the motor. I'm going to pull the line off the strainer that goes to the pump and put a hose in it and see what that does. Hopefully I did not toast the impeller again...it ran for maybe 20 seconds or so...I think I'm sucking air somewhere. I hate trying to run on the muffs, burned up a couple impellers that way...

YYZRC

I’m sure with the boat in the water the raw water pump will work fine. 

earl1z19

The backing plate needs to make solid contact with the side of the impellor as well, that's what makes the score marks in the wear plate. The tolerances in there need to be minimal so it creates a vacuum. I cant imagine you sanded that much of the plate off but it would only take a thousandth or so to create an issue. The sanding may not be the issue and the impellor width could be what the problem is. I would put it in the water and see how it goes from there.

rasbury

@earl1z19im not getting the concern on that backing plate- once assembled the dimensions "inside the pump" would be the same right? The bolts that secure then together might get a little like more of a turn. Now if it is way off being flat I can see that as a problem but even then the o ring should take care of a little of that being off...going to stick the hose in it, we have some really ruff storms inbound so I won't make it to the ramp today and this is killing me!

rasbury

OK, so that worked perfectly. It started right up and I let it run but after two or 3 minutes it stalled out and won't restart. I pulled the fuel water separator and dumped it and still see some water and some trash in it still- some of the fuel in there so I guess I'm going to have to figure out what to do with 50 gallons of fuel....and get it out.

YYZRC

Have you checked your IAC valve to make sure it's not gummed up?

I think your boat needs a good run on plane!

rasbury

YYZRC said:

Have you checked your IAC valve to make sure it's not gummed up?

I think your boat needs a good run on plane!

Oh for sure but I need to keep it running long enough! There is a mixture of some really old fuel. The fuel I dumped was cloudy,  still had water in it along with some other crap! What would I check on the IAC valve? I know of it but not sure what it really does...

YYZRC

IAC regulates the idle. It’s just a spring and a piston. Low tech. 

Maybe increase the idle a little bit when you get it going again. I would stop messing with muffs, though. I would launch it and run it on the trailer. 

rasbury

I will look at that- i was a little shocked to see how crappy the fuel still looked...being punished for letting it sit so long...the problems have been minor really. Aggravating but minor.

The local county waste management will accept 20 gallons at a time from my county residence for free. Guess they don't want us dumping in the back yard...and it's right around the corner-

earl1z19

Probably best to just remove all of the gas and start fresh at this point. New Filters and back to square one with a known good fuel source.

rasbury

Yep....eliminate the basics. Have my siphon all ready to go.