At Anchor

At Anchor
Whiskyjack at anchor in Garrison Bay, San Juan Island

Wednesday, July 2, 2014

Fresh Water Cooling & A Surprise

One of this winter's projects was to add FWC (fresh water cooling) the the Yanmar 2QM15 engine.  Yanmar made this engine for just 2 to 3 years and it was never FWC.  The engine that followed, the "GM" Series, was FWC.  Thanks to a lead from a reader, I ordered a heat exchanger from SenDure Manufacturing ( who had produced a FWC kit.  While they no longer sell the kit, they were more than willing to construct the heat exchanger.

I mounted the heat exhanger by manufacturing "extention nuts" from stainless steel hex stock that replace two of the nuts that hold the exhaust manifold onto the engine head.  Socket head cap screws then secure the heat exchanger mounting clamps to the other end of the extension nuts.

The more challenging part of the project is the added pump.  The original pump will be used to circulate the engine coolant through the heat exchanger, but an additional pump is required to to pump the sea water through the heat exchanger.  I believe that constructing a bracket to mount the pump was more work and trouble than it was worth.  The new method is to use an electric automotive pump (the ones used to cool automobile engines), but that did not appeal to me.  I choose to mount a pump on the front of the engine.  Yanmar made provisions for a PTO (power take off) on the front of the engine vibration dampener.

I purchase a Johnson pump from my local Yanmar dealer and manufactured a mounting flange to mate up with the engine.  I also made a bracket to prevent rotation of the pump.  The whole assembly was then bolted to the front of the engine.

And when it was all done it looked like this!  This picture was taken before the expansion tank was installed on the bulkhead ahead of the engine, the lower left in this photo.

Also visible on the left hand side of the photo is the added valve and hose that allows me to rinse the heat exchanger with fresh water.  The (white) hose has a "garden hose" fitting on the end.  Connect the hose to a fresh water hoes, (or let it pick up form a bucket), close the thru-hull, open the valve to the white hose, and run the engine to flush the system.

The real surprise that I encountered, was that the level of the cooling water in the expansion tank kept going down.  Where was the water going?  After much thought and inspection, I found that the FWC pump was leaking slightly.  Because the engine was raw water cooled and not drawing the coolant from a reservoir, it had gone unnoticed.  A quick rebuild of the pump with a new shaft, bearings and seals solved the problem and everything is running well.


  1. A great boat, I remember falling in love with it at The Vancouver Boat show. I was with Volvo Penta at the time. Later with Yanmar in Vancouver, then Delta. Nice job on the FWC and enjoyed reading .. Thanks for posting. Great find

  2. This may be a couple years too late, but I have the same engine, newly rebuilt, and I'm also looking at doing a FWC conversion. I'm curious where the bracket is positioned to prevent the pump from rotating, and does it work well?

    I'm also curious to know what you used for an expansion tank. I've found a heat exchanger, but I'm still trying to piece everything together in my head.

    1. Adam: I should have included a photo after the installation of the expansion tank! I purchased the expansion tank from Sen-Dure, the same company that manufactured the heat exchanger for me (see page 11 in I mounted the tank on the forward bulkhead of the engine room so that adding coolant would be easy.