Yanmar 3GM30(f)

[Theremedy123]

Hi all, and thanks for having me on board!
Recently my 30 ft Townson sat on a swing mooring for 10 months . Now I have a severe reduction in volume of the salt water cooling system flow. I have purged the lines, checked for air and water leaks in the hoses, inspected the impeller checked the sea Cock is open and not blocked. Still only pumping about 40% of what it used to. I have run Lime through the heat exchanger and found no scaling or blockage there. Can anyone suggest a reason for the reduction in water flow?! Engine is a Yanmar 3GM30F . Thanks!

[Copacabana]

Have you checked the through hull that provides raw water? If it has been sitting for 10 months, you probably have growth in the intake that you will only see when you dive to check the hull.

[AA3JY]

Originally Posted by Theremedy123

Hi all, and thanks for having me on board!
Recently my 30 ft Townson sat on a swing mooring for 10 months . Now I have a severe reduction in volume of the salt water cooling system flow. I have purged the lines, checked for air and water leaks in the hoses, inspected the impeller checked the sea Cock is open and not blocked. Still only pumping about 40% of what it used to. I have run Lime through the heat exchanger and found no scaling or blockage there. Can anyone suggest a reason for the reduction in water flow?! Engine is a Yanmar 3GM30F . Thanks!

Check the raw water pump belt for proper tightness

[Cheechako]

EXHAUST ELBOW BLOCKAGE. Where the water goes into the elbow.

[Wotname]

Originally Posted by Theremedy123

Hi all, and thanks for having me on board!
Recently my 30 ft Townson sat on a swing mooring for 10 months . Now I have a severe reduction in volume of the salt water cooling system flow. I have purged the lines, checked for air and water leaks in the hoses, inspected the impeller checked the sea Cock is open and not blocked. Still only pumping about 40% of what it used to. I have run Lime through the heat exchanger and found no scaling or blockage there. Can anyone suggest a reason for the reduction in water flow?! Engine is a Yanmar 3GM30F . Thanks!

There are really only a few possibilities left.

1. clogged water injection point / mixing elbow
2. impeller not spinning i.e. failed boss
3. one of the items you have already checked is still unserviceable; go back and recheck everything.

You could disconnect the input and output hoses of the raw water pump and rig temporary hoses to a bucket filled with water. Start engine and run for say 30 seconds (the exhaust system can handle a short run). This will tell you if the pump is working correctly or otherwise.

If raw water pump is working, now recorrect the proper output hose to the pump. Keeping the bucket filled and the input temporary hose, run the engine for a minute or two (it won't overheat). This will tell you if the discharge side of the circuit is OK or not.

If still OK, reconnect the input side of the raw water pump and check again.

This process will show which section of the circuit is failing - input side; pump itself; discharge side.

[Copacabana]

After 10 months on a mooring, you can be certain there is growth in the raw water intake. Did you dive to check/clean the intake?

[team karst]

There are two quite easy and definitive tests to do. You likely have 3/4” or so rw hoses. Put a non-wire wrapped hose from the seacock to the strainer. If that hose flattens during a 2000rpm run in neutral, then there is growth blockage towards the inlet.
The other test demands a length of clear vinyl hose from the rw pump to the heat exchanger. If u see bubbles in that hose with the 2000 rpm, then u have a vacuum leak upstream. If these tests pass, then most likely to have a mixer elbow clog.

[Theremedy123]

Originally Posted by team karst

There are two quite easy and definitive tests to do. You likely have 3/4” or so rw hoses. Put a non-wire wrapped hose from the seacock to the strainer. If that hose flattens during a 2000rpm run in neutral, then there is growth blockage towards the inlet.
The other test demands a length of clear vinyl hose from the rw pump to the heat exchanger. If u see bubbles in that hose with the 2000 rpm, then u have a vacuum leak upstream. If these tests pass, then most likely to have a mixer elbow clog.

Thanks to all for the helpful advice! I will try again using your suggestions!
Many thanks! I will post the results!��⛵️

[lockie]

Lots of good suggestions, and a few others. Here's my contribution of some others:


Disconnect the hose from the inlet thru-hull, then open the valve and quickly poke it right through with a long screwdriver or similar. You may find some growth (as I did) within the thru-hull and valve. But you won't see this growth when you dive.


Replace all your RW hoses.


Check your RW pump for drips thru the weep hole at the bottom of the casting. If they are frequent, you might have a lousy seal that allows air to be drawn in and compromises the suction. And tighten all the hose clamps from the thru hull to the suction side of the pump.

[Theremedy123]

Thanks Lockie, I’ve replaced about half of the hoses now, will complete the job next visit and check the seal on the pump gasket, I’m also going to replace the impeller even though it’s not that old just in case. I by passed the engine and ran the pump on it’s own into a bucket , very little water moving through! Thanks!

[Wotname]

Originally Posted by Theremedy123

Thanks Lockie, I’ve replaced about half of the hoses now, will complete the job next visit and check the seal on the pump gasket, I’m also going to replace the impeller even though it’s not that old just in case. I by passed the engine and ran the pump on it’s own into a bucket , very little water moving through! Thanks!

Good to hear you have isolated the problem to the RW pump. This might be a good time to give the RW pump a birthday - replace the seals, bearings and check the front cover for wear / scouring, reverse it if necessary or lap the worn surface. Make sure you are using the proper front plate gasket or O ring. The gap between the face of the cover plate and the impeller must be very very small and the wrong thickness gasket can degrade performance.

While the impeller is new, the loss of performance is not always noticeable but as it hardens or other aspects of the pump wear, an over thick front plate gasket will show up as poor performance.

Additionally, it never hurts to check the water injection point on the mixing elbow from time to time. This will slowly constrict without noticeable affect until one day it becomes very noticeable very fast.

[Theremedy123]

I am really blown away with the level of support and useful advice you all have given! Thanks to everyone, I will post updates as the repairs continue! Then hopefully post a blog and some pics of the coastal cruising I am looking forward to enjoying here in New Zealand! Thanks again everyone!