Piping Coolant to the Hot Water Tank by Paul Andron

Piping Coolant to the Hot Water Tank

Piping coolant from a 3 cylinder fresh water cooled Yanmar engine to a hot water tank is simple. You just need a hot water tank that has piping designed for this purpose. The most difficult thing is finding the correct fittings. I read that the ports on the fresh water pump on a Yanmar are British Standard Pipe Thread. So you have to find a dealer to supply these special fittings. For another helpful resource check out this link:

http://www.boatus.com/goodoldboat/repower2.htm

Here’s what we needed:

Two Brass 5/8 BSPT to 3/8 hose barb fittings, Maryland Metrics, www.mdmetric.com
5 ft of 3/8 inch water heater hose
4 hose clamps
Enough coolant to refill the system after draining it completely.

Step 1. Drain the coolant from the engine. I used an empty washer fluid bottle with a hole cut in the side that fit under the engine. Then I put a spare chunk of hose over the coolant drain valve leading down into the bottle. Then I opened the drain (and the fill) and the coolant fell right out.

Step 2. Flush the system with fresh water. Why not? It’s drained and needs to be cleaned anyway. So I filled it up a few times with fresh water and ran the engine briefly each time to flush the hoses.

Step 3. Drain it all again.

Step 4. Remove the plugs from the FRESH WATER PUMP only. Insert the 5/8 BSPT brass fittings.

Step 5. Cut the hoses to length to run from the brass fittings to your water heater and back. Clamp them in place.

Step 6. Refill the system with the right mix of coolant and water according to the bottle of coolant.

Some important considerations: Coolant is generally poisonous, so make sure your piping inside the water tank is in good condition. The water tank should probably be slightly below the coolant fill cap. If not you will need to move your overflow reservoir somewhere higher because it needs to be at the top of the system. That would require a few more parts and a bit more money. You don’t want air pockets to flow around in your coolant system as that would probably make your engine overheat.