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Not a drop of raw water Yanmar 3GM30F

frosero7744

Member II
Hey guys

I’ve run into a problem I could use some help on from those with far better knowledge than me. After a month of sitting at the slip without being started after Christmas. I went to fire up the motor and take the boat downstream for a visit to the rigger. Started right up like normal and glugged a couple of glugges and stopped. The tone changed to a hollow sound. No water at all was coming out.

Impeller checks outs fine. Raw water filter is clean. I seem to have decent flow at the pump, turning the seacock on and off. As a suggestion I tried blowing through the hose downstream of the pump and I couldn’t blow anything through it.

Is this likely an exhaust elbow? Other things I can check? Engine has always run fine at high rpm’s. No had an overheat. Raw water flow was fine before. The clog was very sudden. PO said he had cleaned the exchanger and the engine ran like that was true.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Have you checked on the impeller inside that little raw water pump on your engine? They have been known to have the rubber vanes either break off or sometimes the whole center rubber part disengages from the little metal hub. Probably a long shot, but it's all I got......
:)
 

frosero7744

Member II
Have you checked on the impeller inside that little raw water pump on your engine? They have been known to have the rubber vanes either break off or sometimes the whole center rubber part disengages from the little metal hub. Probably a long shot, but it's all I got......
:)
First thing I checked. Was hoping it would be that simple.
 

bsangs

E35-3 - New Jersey
Could you disconnect the hose from the exhaust elbow, let it run for a couple seconds see if water comes out through the elbow? Just throwing that out there, not sure how feasible a solution it is. But it could eliminate the elbow from the equation if water comes out.
 

Dave G.

1984 E30+ Ludington, MI
the whole center rubber part disengages from the little metal hub
Look real close at Loren's suggestion. There was a rash of this precise issue. Very hard to visually see, did you physically try to move the impeller when you had the cover off ?
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
Even if the exhaust elbow is totally clogged (unlikely if "raw water was fine" recently), IF the pump is moving water, you should still see a small amount of water exiting the exhaust. This water is from the vent line in the vented loop (usually screwed onto the bottom of the cockpit floor). The vent line would likely still be open even if the exhaust elbow is blocked.

Normally, as the exhaust elbow starts to get restricted from buildup, you will gradually start to see more and more steam, and less water, in the exhaust. It's a gradual process.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Yes, detach the downstream hose from the water pump and stick it in a bucket to confirm flow. Gotta start there.
 

frosero7744

Member II
Look real close at Loren's suggestion. There was a rash of this precise issue. Very hard to visually see, did you physically try to move the impeller when you had the cover off ?
i did spin the existing impeller when i took it off it spit the water out. I replaced it also since i had planned on that anyways.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Probably a silly idea, from afar. But I once used my dinghy foot pump to trouble shoot a long fuel line. I duct-taped the pump hose to the fuel line leading many feet away to the tank, pumped the pump, and my wife could report hearing the gurgling noises inside the tank - so we knew that the one long section was clear. (engine had died and would not bleed out to start). Finally traced problem to the OEM Racor filter and by passed it. Bled out the fuel and engine ran fine, until fall when I replaced that filter assembly.

Now I ponder if one could do something like this to the hose one has removed from the raw water pump? Listen for a gush of air burbling out from under the boat? Perhaps.
Somehow, you have to confirm/check off the parts of the system, section by section, seems like to me.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Should i be able to blow out the output hose?

I don't know, others may. But if the pump drenches you in the test, then the rest is just disconnecting the system downstream until you discover the blockage. It's not routine to have no water output at all, but it is possible that a hose has collapsed, or the heat exchanger gagged, and so on.

Added: the water from the seawater pump goes to the heat exchanger, then through the tubes of the heat exchanger, then out to (probably) an anti-siphon loop, then into the exhaust elbow, then into (probably) a water lift muffler, then through the long exhaust hose to the transom output.* We have repeated reports of issues at the connection to the exhaust elbow; it gets hot, it can accumulate rust and junk. Some exhaust hose sections between the exhaust elbow and the muffler have a one-way valve installed to deter backflow. They can fail closed, or that section of hose can collapse result of the hot exhaust water it has to deal with. (I don't think Ericson routinely installed such one-way valves).

*The seawater path may also go through a water heater along the way.

Hoses, especially big diameter ones, should feel rock-hard to the touch. If you can compress them with fingers they need replacement.
 
Last edited:

Second Star

Member III
I have had a vane from a previous impeller migrate down the hose over time, without altering the flow of water much, eventually get stuck at the fitting to the heat exchanger and then significantly block flow. Concur with all above about hoses etc. Try to use a stick or something to check they are clear if you can't use water.
 

sailing42

Member II
Have you checked that there is a good flow of water coming up from the through-hull to the raw water strainer? This may be a long shot but if you had some growth - seaweed or something else while the boat sat, maybe something is blocking the water inlet especially when the pump is providing suction. You could remove the suction line and put it in a bucket of water to eliminate this possibility.
 
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