Yanmar 1GM exhaust water flow - F25

Boat Systems
1

Hi:

I have a suspicion that I have inadequate water flow through the engine - the amount of water exiting the exhaust at the transome looks miniscule and not what I think a good water flow should be. Last week I had the engine quit on me (it was very hot out, 101 degrees, and I had been running the engine for about 30 minutes at probably 75% rpm as I had to move her to a different marina and there was NO wind to assist), and after a half-hour of cool down, it fired up fine, but then started cutting out and dying again after 10 minutes. None of the guages/warning lights on the engine panel are operative (#116 on the to-do list on this little project boat), and so I am assuming it overheated given the context. It runs fine at idle ever since, but I still have little or no water flow.

My question is, what is a good troubleshooting scheme to try to isolate the problem? Before I break down (no pun intended!) and disassemble the water pump to check the impeller, are there any other steps I should take to find a problem elsewhere first? Also, is there any method out there to “blowback” through the line to clear any blockage that may be present below the waterline at the intake? This is the first inboard diesel I’ve dealt with, so I am operating with a steep learning curve (for now!).

Any thoughts or advice would be much appreciated!

Thanks,
Shawn

2

The steps that I’d take are:

  1. Check the strainer.
  2. Check the through-hull to make sure that it’s not clogged by opening the strainer to check the flow through it.
  3. Replace the impeller. Note that if the impeller has shredded, make sure that you find all of the parts that made it up, otherwise they may be between the raw water pump and the heat exchanger and are blocking the water flow.
  4. Disassemble and rod out the heat exchanger.
  5. Mixing elbow - but this is a last resort as steps 1-3 most likely will resolve it.

– Geoff

3

Thanks Geoff!

I will follow your steps this weekend and see what I can find. Very helpful advice, thanks.

Shawn

4

Shawn -
I had a similar over heating on my F25 but the overtemp alarm did sound.
Turns out the water intake was fowled and needed to be rodded out.
I am considering measuring water outflow peer your suggestion now that the problem has been corrected to establish a good base line water circulation.
By now I hope you problem is resolved.

Cheers,
Jim

5

I feel a little silly responding to a thread which is 12 years old, but somebody else may find this thread. I had similar trouble with no exhaust water flowing. Replaced the impeller, no help. Disconnected the pump end of the hose and opened the cock. No water flow. Kept removing hoses all the way back to the cock. Then I got some water flow! Clearly the problem was a clogged hose, right? Nope.

After reconnecting all the hoses, I discovered that the impeller doesn’t generate sufficient vacuum to prime the pump. I had to close the cock, open up the water filter, and pour water into it until no more water was accepted. Closed the water filter, opened the cock, started the engine, and bob’s your uncle! The winterizing antifreeze started to appear out of the exhaust port! Victory!

The gasket looked like crap, though, so I may have to create a new gasket and re-prime. At this time I know how to do it, and now you do, too!

6

Russ, all I gotta say is you could have posted this in February and it might have saved me from taking apart the raw water system (and while I was at it…the freshwater system, the fuel lines, the exhaust manifold, all the gaskets and hoses). Thanks for the tip though! I’ll be sure to remember it when I get everything back together again :laughing:

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