STEAM from yanmar exhaust?


New member
West Coast
New information to update on this situation.

1. New pump will be way more than $500 around where I live. This provides a strong motivation to find another culprit.

2. At the boat I started sucking on the inlet pipe to see what sort of flow I could get. It didn't start a siphon very well even though all the lines have been removed and individual flow through the pipes has been tested off the boat... Ingress of air perhaps? I removed the only possible thing that could still be leaky, the Groco water strainer, and bypassed this with a hose coupling. No more steam! The Groco strainer looks perfectly fine, but now I'm thinking it must not be holding up under partial vacuum, so the seals are suspect. I'm going to replace the seals and do a vacuum test off the boat before reinstalling it.

I'll let you know if this did the trick. It still doesn't explain why the problems went away for a time once the new impeller was installed. But to save $500+ I'll take this solution any day!


mo fuzz

Super Anarchist
What does a raw water pump cost? Couple hundred bucks? Sounds to me like you've tried everything else likely, and cheap, leaving only the most expensive part.
Try $500. I had one let go the night before departure. No spare. Deck washdown pump plumbed right in and I ran some wire. Ran 14 hours straight. No problems. Why not have electric impeller pumps?
Maybe if you buy OEM Yanmar. You can get a new 3GM johnson water pump for less than $200 from these guys

The oem pumps are made by Johnson. The pumps are exactly the same. If you buy genuine Yanmar, you are paying twice as much for some grey paint.

The original pump on our 3GM wore out its bearings at about 900 hours, and started to leak. Bought a new one from depco, sprayed with a can of Tempo Yanmar Grey engine paint. Voila! Genuine Yanmar pump.

Note, these pumps are rebuildable, but it is kind of a pain. Spending ~$200 was easier.

On the steam ussue:

If you are getting just steam, and very little water out the back, then it is a supply/blockage problem.

If you get lots of water and steam, then I don't know.

If you get a strong smell of coolant, there maybe leaks in the closed fresh water system.

All the problems I have had with steam on my 3GMF have always been pump/supply problems.

One time, a vane broke off the impeller and blocked a port of the pump. The remaining vanes of the impeller just brushed over it. At varying RPMs it would get pushed out of the way. sometimes blocking, sometimes not. It caused a lot of steam when blocking.

One thing I have learned about raw water impellers: dont just remove the cover and look at it from the side. PULL THE IMPELLER OUT and have a good look at it.