Westerbeke W40 Cooling Modification


Over the years our 1981 Westerbeke W40 has had tendency to run a little hot if we pushed it very hard for 30-40 minutes in the summer. If we keep the RPM around2,220 to 2,400 no problem, a constant 200 - 210 degrees.

Years ago I had spoken with the Westerbeke representation at the Annapolis Sailboat show about the problem and symptoms. He had asked if I had a domestic hot water heater installed in the cooling circuit... We do, a Raritan 6 gallon. Next asked about how it was "plumbed" as I explained he smiled and he gave me Service Bulletin Number 95 - Domestic Hot Water Heater. While I had the heat exchanger off to replace the damper plate, I decided it was great time replace all of the hose and finally implement the recommendations in the 1980 bulletin.

After making the modifications I have been able to run the engine at any RPM and maintain a constant 200 engine temperature. I am happy with way this turned out.

Our coolant plumbing was a single circuit with the coolant passing through a remote tank, then into the hot water heater from the hot water heater back into the W40. The line from the remote fill tank to the hot water heater stepped down from a 1- 1/4" hose to 3/4" fitting then back to 1-1/4 after exiting the hot water heater.

The service bulletin suggested the smaller diameter heating coils in the hot water heater reduced the flow of coolant enough to cause engine over heating under certain conditions. To increase coolant flow the bulletin outlined the configuration at the left.
The bulletin called for a 3/8" by pass be installed on W40's with Raritan hot water heaters to provide proper coolant flow.
I built a cross over from black pressure fittings as shown.

Engine lines:          1-1/4"
Hot water Heater:     3/4"
By Pass:                    1/2"
The by pass was assembled with using high temperature steam pipe thread paste.. 
I painted the new system with high temperature engine paint available at any auto parts store. The by pass was then mounted on the bulk head behind the hot water heater.

Per the bulletin I removed the remote fill tank from the circuit and connected it to the highest point of the circuit with a single line, the top hot water heater connection is the highest point in Sea Dragon's cooling circuit.

While I had the tank & hot water heater out, I broke out the wire brush and red engine paint and painted the tank, because well I just have that kind of free time.

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