Yanmar 2gm 20 sea water cooled

bogman

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was working on a cooling problem on a friends boat with a Yanmar 2GM20 sea water cooled engine fitted.
It does not have a vented loop at the exhaust elbow. My last experience with this engine type had a vented loop.
Is it necessary?

It is almost impossible to stop the inlet filter bowl from emptying and it never fills even though we now have adequate cooling
(this is above the static water line....maybe too much.. but I would have thought that the pump could suck enough to fill/prime this filter) )

any thoughts are most welcomed.
 

RichardS

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It is almost impossible to stop the inlet filter bowl from emptying and it never fills even though we now have adequate cooling
(this is above the static water line....maybe too much.. but I would have thought that the pump could suck enough to fill/prime this filter) )

I don't really understand that part. The impeller will suck into the filter as much water as it sucks out so I'm not sure why whether it fills the bowl or not is important. Obviously what is important is that it is sucking in enough water to cool the engine and that appears to be the case.

Richard
 

Tranona

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The problem with the water draining out is either a defective seal in the cap, air leaks in the piping or a worn impeller/face plate. Or a combination. An anti syphon valve is not strictly necessary if the engine is well above the waterline, but it is sensible to fit one.
 

RobF

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It seems that you're asking two questions here...
a) do you need a vented loop at the exhaust elbow.
Tranona has answered this one. Moreover, most engine exhaust outlets are above the waterline and therefore there is no danger of siphoning.

b) the inlet filter bowl empties (I assume when the engine is not running).
This is also normal. Frequently the raw water intake is near the bottom of the boat and the bowl empties once the impeller stops turning. I imagine the water is draining out of the water intake once the vacuum has been lost when the impeller stops rotating.
 

Tranona

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b) the inlet filter bowl empties (I assume when the engine is not running).
This is also normal. Frequently the raw water intake is near the bottom of the boat and the bowl empties once the impeller stops turning. I imagine the water is draining out of the water intake once the vacuum has been lost when the impeller stops rotating.
Not so. If it is correctly installed then the water inlet to the filter is above the outlet, so there is always water in bowl. The only way the vacuum can be lost is if there is leakage as I described in my response. The usual culprit is the cap seal, but a loose clip on a hose or wear in the water pump can also be a cause. The last one can also be a reason for not sucking water to fill the bowl.
 

RobF

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Not so. If it is correctly installed then the water inlet to the filter is above the outlet, so there is always water in bowl. The only way the vacuum can be lost is if there is leakage as I described in my response. The usual culprit is the cap seal, but a loose clip on a hose or wear in the water pump can also be a cause. The last one can also be a reason for not sucking water to fill the bowl.

Thanks for that, something else to check when I'm next on the boat :(
 

pete

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After going through this with my 2gm20f I was still having trouble getting the raw water pump to prime, eventually using a vernier I found the actual body of the pump on its inside back face was worn mainly near the impeller hub ( opposite the face plate) and was not making a good seal. I fixed it with a new pump "ouch". I have not given up trying to get the back face skimmed and a shim fitted to make up the difference and keeping it as a spare.
 
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