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Odd cooling system problems

treilley

treilley

Sustaining Partner
Sometimes when motoring my engine stops pumping raw water. It stops coming out of the exhaust and it sounds like the water lift muffler is dry. I take it out of gear and rev the engine a few times which seems to kick start the flow but stops when it drops back to idle. If I get it flowing and immediately shift into gear and get the revs up, it seems to pump ok. I checked the impellor(new in May) and checked the raw water strainer and both seem fine.

My thoughts are possibly a small air leak in the feed side(seacock to raw water pump intake) of the raw water system that lets air in when at low rpms. Any other ideas?

The Engine is an M25xp.
 
Loren Beach

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Grasping at straws here, but I wonder if the rubber impeller is bonded/attached to its little hub? Next, is the pump shaft turning? (Since it is keyed to fit into a slot, it should be...).
Starting at the intake, is the strainer clear? Old hose section going up to the front of the Universal could have a separated internal wall layer, maybe. Same for the hose to the heat exchanger.

I know of a friend with an internal separation on his exhause hose that would partly block that hose once in a while -- new hose fixed that problem.

Atmittedly, this seems like a puzzle.

Best,
Loren
 
tenders

tenders

Innocent Bystander
In addition to a separated exhaust hose -- a distinct possibility -- it could also be a chunk of rust or other material (broken impeller vane?) pinned somewhere in the system that periodically blocks the raw water flow. When you reduce RPM, you unpin it and it reorients itself allowing flow for a while.
 
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D

Dan Callen

Contributing Member III
Cooling System

My M25XP did this exact same thing and it was a small piece of impellor blade in the heat exchanger. Took forever to figure out but once the exchanger was cleaned everything was back to normal. Hope this helps. Dan Callen Ericson 32-3 Andiamo
 
Shadowfax

Shadowfax

Member III
Also check to see if the plate that you remove to get to the impeller is worn. In time the impeller will wear a groove into this plate and create a blow by situation so that the impeller won't work as well.
Happened to me once.
 
treilley

treilley

Sustaining Partner
All great ideas guys but here is a little more info.

This is our 3rd season and our 3rd impellor. All came out intact. This winter I replaced the water heater and also cleaned the HE.

I will next replace all the hoses leading to the raw water pump. They are old and cheap to replace.


I guess if something is clogging the downstream hoses or chambers then the pump with stop circulating water. But at one point I opened up the strainer and was able to pour water into it and the pump sucked it through. Maybe an air leak in the strainer. The gasket is good so it must be something else. I did remove the strainer and clean it our and store it indoors this winter so no chance of freezing damage.
 
Shadowfax

Shadowfax

Member III
Another thing to check is where the hose from the heat exchanger enters the riser. Sometimes this gets clogged up with exhaust gunk. Remove the fitting tapped into the riser where the hose enters and stick a screw driver in the hole and move it around breaking up the stuff if it's there. Start the engine and you should get a shot of black gunk out the exhaust. If so, that was probably the problem
 
H

hodo

Member III
Also check and see if you have the bronze check valve in line between the riser and the water lift muffler. I just solved a friend's similar problem by removing the flapper that had worn through the pivot, and would occaisionally blow into where it would restrict the exhaust.It seemed to do it only under power, but at idle would fall away and be okay.
Harold
 
Steve

Steve

Member III
Intake Air Leak ?

:confused:Had a similar issue, it was a cracked softened intake hose connection at the pump, thus it was sucking air. Apparently it doesn't take much air to break prime. This happen while on a cruise, just cut off several inches and all was well, replaced the complete hose back to strainer when we returned, also added a tee with hose fitting/cap so we can run fresh water for a flush or run the engine on the hard.
 
G

Glyn Judson

Moderator
Moderator
Odd cooling system problem.

Tim, Good call to replace the raw water intake hoses. Last summer I lost all sea water cooling to my Yanmar 3GMF and it was caused by an old intake hose. I replaced all those hoses back in 1996-7 and as they were USCG approved, never gave them a second thought. The culprit turned out to be a blister in the inner lining of the hose between the seacock and the strainer. The heck of it was that it'd only block the intake water at higher RPM's. When revving down the blister would diminish and the water would happily flow again. I replaced ALL of those hoses, three in my case and the problem was solved. Hope this helps, Glyn Judson, E31 hull #55, Marina del Rey, CA
 
P

pick

Member II
The previous owner of my boat had a difficult-to-solve overheating problem. It turned out that the thingy inside the Oberdorfer pump that deforms the impeller was worn. Luckily it is replaceable.
 
E

Emerald

Moderator
pick said:
TIt turned out that the thingy inside the Oberdorfer pump that deforms the impeller was worn. Luckily it is replaceable.
Click to expand...

That thingy is called a shoe (at least that's what I've always heard it called). You can even change the characteristics of how the pump works - flow and pressure - by changing that thingy. Got a shoe thingy from Featherman Enterprises when I rebuilt my pump. Worth giving him a shout:


http://www.feathermanenterprises.com/


and for the record, no affiliation or anything to gain financially - just a really happy customer.
 
treilley

treilley

Sustaining Partner
I replaced the hoses from the seacock through the raw water pump today. When doing so I found that the hose on the input side of the strainer was loose. I removed the strainer this winter and I guess I never tightened the clamps enough. They were pretty tight but I was able to remove the hose without loosening them. The hose was also fairly deformed from the barb.

Well, so far so good. The engine pumped water fine at low rpms. We will see if it continues to work as the problem was very intermittent.
 
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