Raw Water flow rate low....

CTOlsen

Member III
I've noticed my raw water discharge overboard flow rate has decreased over the last ~3 seasons. After the engine has heated up, the overboard flow is hot enough to show vapor (not just water) coming from the overboard line. Running temps are good, < 180 deg. I've inspected the suction screen, strainer, and the heat exchanger and don't see fouling. I replaced the impeller this spring and it had no effect.
I plan to disconnect the raw water hoses and have a look see inside, I have a small borescope I can use as well. Has any one seen this before? What are your thoughts on where the problem lies?
 

Christian Williams

E381 - Los Angeles
Moderator
Blogs Author
Likely the heat exchanger needs boiling out, even if it looks OK. Standard maintenance every 5 years or so and the first place to start. Lots of threads on the subject.

 
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Slick470

Member III
Craig, Which engine do you have? On our Yanmar, if the raw water injection port to the mixing elbow gets clogged with bio goo, it can reduce flow out the exhaust. If the restriction is high enough, water will start coming out of a thru hull on the stern that is tied to a vented loop ahead of the elbow.
 

footrope

Contributing Partner
Blogs Author
Yes, as Andy says, check your exhaust elbow for clogging, both the raw water port and the exhaust passage itself. A friend of ours with a Yanmar had to clean his injection port at the start of every season.
 

Slick470

Member III
I will warn however, that the smell of the mostly cooked and compacted remains of the little creatures that were clogging up ours gave replacing head hoses a run for the money. Also wear gloves, if you get any of that goo on your hands, your significant other might not let you any where near them until you get that smell to leave, and it was persistent.
 

CTOlsen

Member III
Craig, Which engine do you have? On our Yanmar, if the raw water injection port to the mixing elbow gets clogged with bio goo, it can reduce flow out the exhaust. If the restriction is high enough, water will start coming out of a thru hull on the stern that is tied to a vented loop ahead of the elbow.
I've got the original Universal 25XP. I replaced (had replaced) the mixing elbow 2 seasons ago, not because of fouling, but had developed a through-wall leaker.
 

toddster

Curator of Broken Parts
Blogs Author
Maybe strategic disconnection of hoses along the flow-path cold help pinpoint the source of the problem?

Another possible culprit that I've encountered is wear on the cover-plate of the pump. Even a tiny groove will let water go around the impeller blade instead of through the output - especially if there is any back pressure. Lapping the plate smooth again on a piece of fine sandpaper sometimes fixes the problem.
 
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