yanmar 2gm water blocked

[Ardenfour]

When I first fired up the engine on my new to me boat I had no water out the exhaust. Replaced the impeller, and tracing the pipework led to the thermostat housing. I took this off and found the water passage behind completely blocked with salt, the surrounding pipework likewise. I cleared all this with wire and screwdrivers and water now exiting exhaust. Have used the engine for a few hours and no sign of overheating. However if I open the drain plug on the block nothing comes out, I've prodded around in the hole and it seems clear as far as I can reach. So it would seem the water passageways are still blocked in places.
How best to clear this, without major dismantling? Engine is a 2GM20, raw water cooled. Thanks.

 

[Mel]

Try to back flush with a hose from domestic supply ---- remove drain valve ---- connect hose to a top water connection of the engine with thermostat removed.
You should see debris come out from drain hole.

There are chemicals that are often used to clear out raw water systems - blockage is often a calcium carbonate and should move with "Rydlyme"
If you can fill and soak with this prior to back flushing you should achieve a good result

 

[nathanglasgow]

Had this problem with a Yanmar on a previous boat. Found that mechanical rodding of water passageways was the best and most thorough way of clearing corrosion. Taking the head off is not too hard to do,might be a good idea to do it anyway as I don't think the engine on your new Nic 30 has been run for about 3 years. Would give you a chance to go through the top end and rebuild with new gaskets. Maybe £100 in parts and then you know you have a reliable engine.