Changing the impeller on a sun odyssey 379?

[paparon]

When we changed the impeller on our sun odyssey 379 about 6 litres of water escaped despite the fact that we had closed the sea cock on the sail drive. How do you stop water from escaping when you remove the impeller? 

[so36idavid]

I think your engine is a Yanmar 29, which is the same as I have. The short answer is that you can't stop water from escaping. You're opening up a hole in a thing containing water  . 6l sounds like really a lot, I lose maybe 1 or 2. It's possible that you have a lot of water in the debris filter that's somehow draining out, but there's really not that much raw water piping on the engine. You say you closed the seacock so there's a bit of mystery where all the water came from.

Anyway, the solution isn't too bad. Since you can't stop the water from escaping, it's a matter of dealing with it when it does. I have a big towel and a shallow tray that fits under the engine. Try to get as much water into the tray and anything that doesn't should hopefully land on the towel. When the water has done draining, extract the soggy mess and dump the water overboard. Anything that got touched by saltwater gets a fresh water wipe down and maybe dried with a rag. 

[alenka]

Loss of this water should be no big deal other than you end up with a little sea water in the bilge which can be easily pumped out. 6 litres in the overall scheme of things is not a lot.

If your concern is regarding the impeller running dry, a liberal amount of grease on the impeller should lessen the strain until the system has self primed.  I know some engineers prime the system by closing the sea cock and filling the pipes up through the strainer, opening the sea cock when the boat is in the water and just prior to engine start.

My chum forgot to do this once in the hurly burly rush of the launch and I can tell you impellers don't last without any water going through them for a minute or so... but I have always found allowing them to self prime is not a problem.

[jdl01]

With the boat in the water, you will always loose the volume of water in the raw water strainer, but 6 litres is a lot. Our strainer liquid level is usually only a couple of centimetres when the engine is off and the boat level. Johnson pumps recommends a little glycerin on the blades of a dry impeller and filling the strainer to the top while the drive leg seacock is still closed should reduce the chances of an air lock when you restart the engine. I try to coordinate my impeller checks with haulouts and thus avoid the seawater loss issue.

[redwoodsca]

Having changed my impeller on my 3JH5E this weekend that fun process is fresh in my mind.  I find that if I pop the top on the sea strainer then it is less of a closed system and less water leaks out.  I was still a lot more water than I would have expected. I loosen the screws on the impeller pump plate until it leaks from one lower side then transfer from a cup to a larger container.  Felt like forever to get all the water out.  Purchased the impeller from www.staycoolpumps.com/index.html which sells through Amazon also.  Appears to be good quality and definitely good customer service.

[alenka]

A quick, slightly off-topic, question... How often do you change your impeller and engine belts?   I have been changing mine at the end of every season but is there really that much need? I wouldn't dream of changing belts on my car after just a hundred hours or so.

[jdl01]

I go for the 'inspect annually - replace as necessary' school of maintenance. Look for black dust in the v belt area and potential small cracks in the vertical axis of the belt itself. Pull the impeller and check for cracks or chipping. If nothing is showing, lubricate and replace. We have 8 month seasons - so I get 3 years or 24 continuous use before I need any changes as a typical average.

[so36idavid]

I've had two impellers throw blades in the last four years. Then you have to go open the heat exchanger to find them, not horrible but not pleasant. I now change impellers every year, cheap insurance. 

Honestly I don't know what's going on with these impellers, I think I probably got old stock that had been sitting on the shelf for a few years. 

[ForGrinsToo]

Yanmar 3YM30
Annual change of the impeller prior to spring launch, 4-month season, probably 150 hours per season.
Belts 3 to 5 years, but look for black dust around the pulleys and on the engine.

As far as the impeller, it will "set" if it sits for long periods (over the winter) and lose a good bit of efficiency. I agree with David: it's a really small cost in the grand scheme. And I carry two spares (as well as spare belts).

6L seems a lot. 1L, maybe 2, is what I would expect based on the strainer and the hose lengths in the 36i setup.

Geoff

[paparon]

Many thanks for all of you replies. Very helpful. Paparon.

[artboas]

Dec 5, 2018 20:51:12 GMT ForGrinsToo said:

Yanmar 3YM30
Annual change of the impeller prior to spring launch, 4-month season, probably 150 hours per season.
Belts 3 to 5 years, but look for black dust around the pulleys and on the engine.

As far as the impeller, it will "set" if it sits for long periods (over the winter) and lose a good bit of efficiency. I agree with David: it's a really small cost in the grand scheme. And I carry two spares (as well as spare belts).

6L seems a lot. 1L, maybe 2, is what I would expect based on the strainer and the hose lengths in the 36i setup.

Geoff

[artboas]

Here is a very good tip...
You should install a cheap coarse water strainer on the output hose of your water pump. This will catch any broken impeller bits, etc. Sure a lot easier than trying to fish them out of the heat exchanger!