Engine Heat for Hot Water

Big Duck had a pair of open copper lines in the engine compartment when we got her. We figured these were at one time plumbed to the water heater water to use engine heat to make hot water, but because we had a 3000i generator which was wired to make hot water, I was not inspired to install hoses to make the water heater work with engine heat. I guess I was also a little leery about clogging up my engine access with hoses running hither and yon.

open copper lines in the engine compartment

Well, I finally decided to give this engine heat thing a try. I first pressurized the copper lines with hose water to test the integrity of the system. I connected one of the copper pipes directly to the hose -- the other copper pipe was connected to a hose shut off valve. I turned on the hose water a bit and let it run free to start, then using the shutoff valve I restricted the flow just enough to create a little pressure in the system...after a couple hours the bilge was still dry and I was satisfied that the system was in tact.

The instructions say to take the engine hot water feed from right under the thermostat. I had a temperature sensor right there, which I planned to "T" into to send engine heat to the water heater. The return from the water heater would go to the 9 o'clock plug on the circulation pump.

The open copper lines take a 5/8” hose nicely so that’s how I decided to set up the system. All I’d need was a 5/8 barb to ½ pipe for the circ pump return, a 1/2 pipe nipple and “T”, and a 5/8 barb to ½ pipe to get both the feed and temp sender plumbed just under the thermostat in the old temp sensor hole.

The return line to the circ pump was a no brainer, but when I tried to fit the “T” under the thermostat for the hot feed and temp sensor, there was not enough clearance to bolt down the thermostat housing. If I was going to go this route, I’d need to make a ½” spacer to fit between the intake manifold and the thermostat housing to get clearance for the “T”.

no clearance between the temperature probe and thermostat housing

I didn't have any ½” aluminum to make the spacer so I dialed up eBay to find some stock. On a whim I searched for thermostat spacer and I’ll be darned if some didn't turn up – and they were for the Chevy small block.

The spacer even came with a 3/8” pipe port for the 5/8” hose barb, and I ordered up the fitting. Now I could leave the temp sensor in it’s original home and take the hot feed from the spacer.

spacer with tapped hole for water heater water

temperature probe in place with room from spacer for hot engine water to water tank

Knowing I’d need to make provision for winterization of the hot water engine heat system, I incorporated brass hose fittings in both the to and from hoses so I could easily detach them from the copper pipes and then connect them together if I wanted to run the boat without sending water to the heater.

And, because I hate gouging myself on those bands that protrude from hose clamps, I used Clamptite clamps on the brass hose fittings. 

Clamptite clamps   http://www.clamptitetools.net/

And the hoses were tucked away so they wouldn't interfere with access to the motor.

Now we were cookin' with engine heat for hot water, easy winterization and the ability to not feed hot engine water water to the water heater if we were winterized and wanted to go out for the weekend.