Seawater not pumping through engine

[K2MSmith]

I've got an M25 which starts and runs great but seawater suddenly stopped flowing through the engine. Here is what I tried so far:
- disconnected input hose (that goes to thru-hull) from water pump on front of engine; and blew water through it through a garden hose. It appears clear - least going out;
- i was able to suck water in through the input house (connected to the thru-hull.)
- took cover off of water pump and cranked engine a few rotations, verified that impellor is turning.
- replaced impeller (old one looked good, but I happened to have a new spare anyway).
- there is a screw plug on the pump housing, I removed that and cranked engine to see if water would come out. No water (?).
- there is no raw seawater filter in the system.

The back end of the system is not easily access from the front of the engine, so I have not tried to diagnose anything on the output side of the pump. Is it possible that with all I have checked, the pump still doesn't actually work ? Next thing I was thinking of trying was buying a piece of 2-3' hose, removing the output from the pump and replacing with the spare hose going into bucket to see if I can start the engine and fill the bucket.

Any other ideas ?

 

[Frank Langer]

I've got an M25 which starts and runs great but seawater suddenly stopped flowing through the engine. Here is what I tried so far:
- disconnected input hose (that goes to thru-hull) from water pump on front of engine; and blew water through it through a garden hose. It appears clear - least going out;
- i was able to suck water in through the input house (connected to the thru-hull.)
- took cover off of water pump and cranked engine a few rotations, verified that impellor is turning.
- replaced impeller (old one looked good, but I happened to have a new spare anyway).
- there is a screw plug on the pump housing, I removed that and cranked engine to see if water would come out. No water (?).
- there is no raw seawater filter in the system.

The back end of the system is not easily access from the front of the engine, so I have not tried to diagnose anything on the output side of the pump. Is it possible that with all I have checked, the pump still doesn't actually work ? Next thing I was thinking of trying was buying a piece of 2-3' hose, removing the output from the pump and replacing with the spare hose going into bucket to see if I can start the engine and fill the bucket.

Any other ideas ?

If you run the engine with the output hose in a bucket to test, as you suggest, you may want to add lots of petroleum jelly or other lubricant to the impeller to keep it from being destroyed. I understand that it can deteriorate quickly.
Is it possible your heat exchanger is plugged if it hasn't been cleaned recently? No kinks in any relevant hoses?
After no water in the exhaust, I have to rev the engine a bit to restore prime/flow. Without that, I had no exhaust water although everything was good, but once I revved it a bit it worked as normal.
Frank

 

[K2MSmith]

If you run the engine with the output hose in a bucket to test, as you suggest, you may want to add lots of petroleum jelly or other lubricant to the impeller to keep it from being destroyed. I understand that it can deteriorate quickly.
Is it possible your heat exchanger is plugged if it hasn't been cleaned recently? No kinks in any relevant hoses?
After no water in the exhaust, I have to rev the engine a bit to restore prime/flow. Without that, I had no exhaust water although everything was good, but once I revved it a bit it worked as normal.
Frank

I tried revving the engine but that didn't help. The diver who cleans the bottom is also going to check the thru-hull for me to make sure they are clear.

 

[Kenneth K]

I've had the problem of no water pumping when there was air between the thru-hull inlet and the pump inlet. Prime the line (make sure it's full of water) then try your idea of putting a temporary hose on the pump output. If the pump works, you'll just have to progress hose-by-hose and component to find the blockage.

 

[K2MSmith]

I've had the problem of no water pumping when there was air between the thru-hull inlet and the pump inlet. Prime the line (make sure it's full of water) then try your idea of putting a temporary hose on the pump output. If the pump works, you'll just have to progress hose-by-hose and component to find the blockage.

Good ideas . The pump cover has been missing a screw which I dropped into the engine compartment a year ago and have not replaced. I’m thinking that I need to find a new o-ring and a replacement screw now that I hear they can leak air and become airlocked . Trying all the simple things first before I have to go crawling into the “coffin” to debug the back end .

 

[dcoyle]

Since you said there was no water coming out of loosened bleed valve on pump housing, that means there is no water making it to the pump. I had an issue similar to this a number of years ago and it turned out to be dirty inlet on hull. Would pump water at 1500 rpm but would get clogged at anything higher. Im guessing you may have similar issue. I would think even if system is airbound you would still get water at raw water pump. Good luck!

 

[Joliba]

If all is clear leading to the pump but it won’t prime, use PTEF marine grease liberally on the impeller vanes and try again. Vaseline can degrade some types of rubber, so should not be the first choice. Of course closing the pump cover with an intact o-ring or gasket and all the screws is also important.
This tip has worked for me in the past.

 

[K2MSmith]

Since you said there was no water coming out of loosened bleed valve on pump housing, that means there is no water making it to the pump. I had an issue similar to this a number of years ago and it turned out to be dirty inlet on hull. Would pump water at 1500 rpm but would get clogged at anything higher. Im guessing you may have similar issue. I would think even if system is airbound you would still get water at raw water pump. Good luck!

Good points . The diver is going to clean the inlet on the hull side .I’m not sure I tested properly with the bleed screw . I actually took it out completely and ran the motor , but didn’t get any water out of it . - but that wound introduce air in the pump (?) maybe I don’t understand the purpose of the bleed screw . It would kinda be good news if there was no water at the pump, then we know it’s a clog in inlet side or pump is not sealed properly. I’m going to the boat tomorrow to do further tests .

 

[Christian Williams]

I would yank the output hose off the water pump housing and start the engine.

That ought to spray water all over the place for as long as it takes to yell "shut it off!".

If not--the issue is the pump. If water does flow, I'd go next to the output hose of the heat exchanger, which also ought to spurt. And so on downstream.

The simplest, and theoretically therefore probable, is an issue with the pump. The rest of the system even when gummed up usually lets some water through.

 

[K2MSmith]

I would yank the output hose off the water pump housing and start the engine.

That ought to spray water all over the place for as long as it takes to yell "shut it off!".

If not--the issue is the pump. If water does flow, I'd go next to the output hose of the heat exchanger, which also ought to spurt. And so on downstream.

The simplest, and theoretically therefore probable, is an issue with the pump. The rest of the system even when gummed up usually lets some water through.

 

[K2MSmith]

I wanted to try your suggestion, but whoever put the output hose clamp on last rotated it into the strangest position that I could find no tool in my box to reach the tightening screw. I’ll have to find a small universal joint for a socket wrench or find a new socket for a flexible spring shaft screw driver gizmo I bought for hose clamps which almost went in the recycle bin because they designed it to use non-standard sockets.

 

[bigd14]

See if you have any sharp elbows in the system. Old impeller vanes can get caught there and still allow water through for years. But perhaps one shifted and is now blocking flow? I found one. Replaced the elbow with a straight fitting.

 

[Bolo]

I've got an M25 which starts and runs great but seawater suddenly stopped flowing through the engine. Here is what I tried so far:
- disconnected input hose (that goes to thru-hull) from water pump on front of engine; and blew water through it through a garden hose. It appears clear - least going out;
- i was able to suck water in through the input house (connected to the thru-hull.)
- took cover off of water pump and cranked engine a few rotations, verified that impellor is turning.
- replaced impeller (old one looked good, but I happened to have a new spare anyway).
- there is a screw plug on the pump housing, I removed that and cranked engine to see if water would come out. No water (?).
- there is no raw seawater filter in the system.

The back end of the system is not easily access from the front of the engine, so I have not tried to diagnose anything on the output side of the pump. Is it possible that with all I have checked, the pump still doesn't actually work ? Next thing I was thinking of trying was buying a piece of 2-3' hose, removing the output from the pump and replacing with the spare hose going into bucket to see if I can start the engine and fill the bucket.

Any other ideas ?

I was re-reading your post with my morning coffee and I think that you’re trying to think of every possible problem at one time. You need to be systematic about solving this problem. I know you know this but it bares repeating. Fist off, you said, “seawater suddenly stopped flowing through the engine” which to me says a sudden change in something. My first thought is a clog at the seacock. You mention that you, “blew water through it through a garden hose”. Do you mean that you took the hose off the seacock, opened the valve and then blew water OUT of the boat? If you did this did you first try taking the hose off the seacock and then opening the valve to see if water flows into the boat? I had a clog in a seacock once that feed the AC on my boat. No water would come through the open seacock but when I pushed a threaded rod I had on board through it there was no resistance and a little water came through. Turns out it was a jelly fish stuck over the outside of the seacock that acted like a flap. Not saying that this is your problem, just asking if you opened the seacock without any hoses, garden or otherwise, attached? The other big blockage point possibility would be the heat exchanger. When was it cleaned out last? But even this wouldn’t account for a sudden loss of water flow.

 

[Loren Beach]

Try as I might, no "ah ha" moment comes to mind. Frustrating.
Starting at the hull intake, can the "engine water system" be inspected? Is the actual inlet seacock really open? i.e. no plastic bags, no jelly fish, and no old "grate" over over the opening that has partly closed up due to sea growth over time? Hoses new enough that there is no chance of an interior liner loosening and causing an 'aneurysm' (happened to a friend of mine with an ancient exhaust hose)? Pump working? Next hose and the HE passing water thru?
Emphasis on trouble shooting the water path, one link at a time.

FWIW, I did add a Groco brand raw water strainer to our engine intake system soon after be acquired the boat. We've occasionally caught some bits of seaweed in it, but luckily nothing huge.
Keep posting... there's gotta be a solution!

 

[K2MSmith]

I would yank the output hose off the water pump housing and start the engine.

That ought to spray water all over the place for as long as it takes to yell "shut it off!".

If not--the issue is the pump. If water does flow, I'd go next to the output hose of the heat exchanger, which also ought to spurt. And so on downstream.

The simplest, and theoretically therefore probable, is an issue with the pump. The rest of the system even when gummed up usually lets some water through.

Looks like the problem is more back end .

 

[Christian Williams]

Progress.

Everybody is now thinking the same thing: something clogging the run of hoses and heat exchanger. Test them one by one.

I recently changed all the hoses on my cooling system, and here's what I learned:

--For access, remove stuff in the way. In my case, the waterlift muffler and its big exhaust hose. If necessary, the water heater, too. Its an hour's work, and that's the first thing a boatyard does at $130/hour.

--Specialty tools really help for this work, notably a small socket wrench to fit the many hose clamps (forget a screwdriver in confined spaces). Some old hoses are fused to their barbs or stubs. For that, a 10-dollar “Drake Off Road 4521 Hose Removal Tool” is a luxury. A heat gun is required too, along with towels for spillage for the inevitable mess of drained fluid, raw water and knuckle blood.

--I'd probably start by taking out the heat exchanger. It should come out anyhow, so you can properly clean it of scale. And it may well be the problem.

Here's more on my experience, with links to Hx boil-out in the Comments section.

Marine Diesel Cooling System Upgrade 2020

Symptoms: Apparent decrease in water volume at exhaust. Temperature RPM limitation at Wide Open Throttle. Steam from exhaust at idle. Solution: clean heat exchanger, optional general upgrade. [Note 2024: For routine maintenance of the cooling system I later had success with the immersion...

ericsonyachts.org

 

[K2MSmith]

Progress.

Everybody is now thinking the same thing: something clogging the run of hoses and heat exchanger. Test them one by one.

I recently changed all the hoses on my cooling system, and here's what I learned:

--For access, remove stuff in the way. In my case, the waterlift muffler and its big exhaust hose. If necessary, the water heater, too. Its an hour's work, and that's the first thing a boatyard does at $130/hour.

--Specialty tools really help for this work, notably a small socket wrench to fit the many hose clamps (forget a screwdriver in confined spaces). Some old hoses are fused to their barbs or stubs. For that, a 10-dollar “Drake Off Road 4521 Hose Removal Tool” is a luxury. A heat gun is required too, along with towels for spillage for the inevitable mess of drained fluid, raw water and knuckle blood.

--I'd probably start by taking out the heat exchanger. It should come out anyhow, so you can properly clean it of scale. And it may well be the problem.

Here's more on my experience, with links to Hx boil-out in the Comments section.

Marine Diesel Cooling System Upgrade 2020

Symptoms: Apparent decrease in water volume at exhaust. Temperature RPM limitation at Wide Open Throttle. Steam from exhaust at idle. Solution: clean heat exchanger, optional general upgrade. [Note 2024: For routine maintenance of the cooling system I later had success with the immersion...

ericsonyachts.org

Thanks for the info and thread Christian. That address for the radiator shop you used in LA (Blanco Brothers) looked familiar and as it turns out its just a few blocks from my mother-in-law’s house in Koreatown. The Drake tool looks like an oversized dental pick. Not sure how to use it, but it‘s cheap enough to order. (and all the tools I’ll ever need will cost must less than a trip to the marine diesel mechanic). You’re right about getting a small socket wrench..I ended up buying a small 3” 90 degree ratchet screwdriver wrench, but I think just a small 1/4 socket wrench would work better (which I don’t apparently have)... Add an LED headlamp to the list, especially with my poor near vision.

 

[Christian Williams]

 

[Kenneth K]

If your engine is an M-25, it appears you still have the "over-the-top" alternator bracket that once came as OEM. Are you aware of the recall on that alternator bracket and the steps for getting it replaced? Lots of info posted about it here on the forum.

 

[G Kiba]

If your engine is an M-25, it appears you still have the "over-the-top" alternator bracket that once came as OEM. Are you aware of the recall on that alternator bracket and the steps for getting it replaced? Lots of info posted about it here on the forum.

Oh my. Another thing for the boat project list?