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Water Suction Problem

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supabribri

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"I have a volvo aq170/270. I h

"I have a volvo aq170/270. I have hooked the boat to muffs, and I get no water flow. I pressureized the suction pipes and found that it was leaking at the hose connector. I replaced the connector and the seal. I also found a crack in the copper piping, which I fixed. I replaced the impeller also. The boat wont suck water. However if I disconnect the suction hose and place it in a bucket of water, it sucks it up just fine. So I pressurized the system again and I cannot find any leaks???? What am I missing?"
 
"Yeah, I went thru that whole

"Yeah, I went thru that whole post. That's actually how I fount it was the hose connector, and How to pressureize the system with the garden hose. However I see NO Leaks when I do this? Is it possible the impeller is to weak to draw water from that distance? Can I just drill a hole and run a tube past the water line bypassing the the leg, and the hose connector and all those problems? Is there some way (when pressurized with the hopse) the water is leaking into the cavity where it normally picks up the water? In otherwords, if I drop the boat in the lake will it work?"
 
"Some people run through-hull

"Some people run through-hull raw water intakes, but my personal advice is to keep using the outdrive's. The system has been working for years on your boat, so yes you face a challenge to find where the problem is. However, there are only so many places between the raw water hose and the intake grids that can cause a problem.

As a test, you may want to install a piece of clear plastic hose between the raw water pipe attached to the inside of the transom shield and the copper pipe attached to the raw water pump and see if you get vacuum or air bubbles. If you get neither air nor vacuum, then either the raw water pump impeller is NG or there is a blockage int eh exhaust manifold, water strainer, or heat exchanger. If you get air bubbles, then you have to identify the source.

Also, try to use a large bucket rhather than ear muffs, as the pump could be sucking air through the drain hole at the bottom of the outdrive, especially if there is little water flow through the garden hose."
 
"El, Thanks for all your advic

"El, Thanks for all your advice. Can I assume since it will pickup water from a bucket attached to the copper tubing that I do not have a problem with the impeller, or blockage somewhere? I will try the clear tubing and let you know what I find. Thanks!"
 
"So this is what I found. If

"So this is what I found. If the suction line is primed, it works fine. However if the suction line is not primed it won't work (suck). So when I turn off the motor and take the leg out of the bucket of water, and the water drains out. and i put it all back it will not suck up the water, but if i prime the system full of water first it works... Could the impleller be to weak? I did replace the rubber and the gasket.. that's all there is to it right??"
 
"If you have replaced the impe

"If you have replaced the impeller and the seal, you may have a source of air ingress somewhere between the raw water pump and the outdrive. I assume you installed the woodruff key correctly in the raw water pump?"
 
You might even simply have a w

You might even simply have a worn out impeller housing and cam in the pump. New impeller in a scored housing might not seal off properly.
Can You post a pick of the inside of the pump?
 
"Here is the picture. I did n

"Here is the picture. I did notice that the impeller shaft is a little loose and is scored, would that make a difference?

148987.jpg
Impeller Housing
 
Looks ok.
Did You use an &#39

Looks ok.
Did You use an 'original' impeller or an aftermarket? It is important that the impeller 'seals' off properly towards the lid as well at the bottom.
If You remove the hose from the drive connector and 'extend' it into a water bucked with water how low can You have the bucket before it does not manage to suck? Use a clear plastic hose and it is easier to monitor from outside.
Remember to grease or 'soap' the impeller before installing.
 
anything lower than about 12 i

anything lower than about 12 inches requires me to prime the system. The impeller is a volvo penta part and is brand new.
 
"If that is 12 inches below th

"If that is 12 inches below the water connector on the drive, I guess it will be well below the waterline when boat is floating. Then it should not be a problem."
 
Sorry I meant 12 inches below

Sorry I meant 12 inches below the impeller pump. I need to prime the system even if the boat is floating. Wierd eh?
 
"Is it the same problem if You

"Is it the same problem if You loosen output from pump?
The reason for the question is that excessive exhaust back-pressure may be higher than what the pump manages to deliver. If water can not get out -it may not get in. Have come across this problem when exhaust by-pass in transom has been blocked/missing or exhaust bellows with valves have been installed together with drive with rubber flap. A slightly weak starter does not manage to push out when cranking, and pump does not work at low rpm. It might even be a partly blocked exhaust elbow not letting the water out properly."
 
That was a good test. I unhoo

That was a good test. I unhooked the pressure hose going into the oil cooler.... and it pumped great. I just have the standard bellow. How would I go about testing the other items? Just take the elbow off and check to see if there is any blockage?
 
"My mind is still going. How

"My mind is still going. How is it possible that it works when I prime it? If I prime the system, and the boat is in the water, I can turn it off and when I start it back up again it works fine. Really the only time it stops working is when the system is pulled out of the water then placed back in. Could there be an air leak into the oil chamber? Or back into the water system?"
 
"When You drain the system, th

"When You drain the system, the pressure/suction by the pump is working against/with air cushions. The pump efficiency in air is just fractions of when working in water. On the pressure side the air will just be a cushion or 'shock' absorber. Unless You manage to 'compress' the cushion on the pressure side enough for the water on suction side to reach the pump, You will experience what You are doing."
 
thanks Bob N. I bought the muf

thanks Bob N. I bought the muffs off ebay. I've always used a big bucket. this should be easier!!!
 
"Abe, those muffs were just an

"Abe, those muffs were just an example. I don't know what outdrive / outboard they fit. You may have to modify them to fit on your outdrive. Just a heads up..."
 
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