1994 390CPMY water heater replacement

[Viper]

I wonder how much heat loss there is though going through the lines. The tank distance from the engine/length of the lines would make a big difference. Out of curiosity, I'll have to read the output line at the engine and compare to the line entering the tank. Half of my circuit would probably be close to 20 feet of hose, with about half of that in the lower areas of a hot engine compartment while running.

[tonyiiiafl]

Since the lines go to starboard engine a good 8’ of hose.

[bud37]

QR_BBPOST I always thought it was interesting/weird that you get hotter water from the heat exchangers than from the electric elements. Makes sense though, as the engines are regulated at 160-180F, much higher than the usual water heater thermostat.

Consider where the takeoff is for the water heater....... generally engine circ pumps are pumping the coolest water/coolant thru the block then out the thermostat to the rad/heat exchanger or lake depending on the system you have. So in that case the water heater would see the cooled coolant in a closed system if taken from the pump housing.....then for sure there are losses in the hose......just a long heat exchanger to air really.....the way I see it anyhow......

[tomschauer]

We only turn on the water heater when we need hot water. 15 minutes and plenty of hot for a shower and dishes. I don't leave it on all the time.
If running the boat, we of course, have 160-170 degree water in the tank.

[km1125]

QR_BBPOST

QR_BBPOST I always thought it was interesting/weird that you get hotter water from the heat exchangers than from the electric elements. Makes sense though, as the engines are regulated at 160-180F, much higher than the usual water heater thermostat.

Consider where the takeoff is for the water heater....... generally engine circ pumps are pumping the coolest water/coolant thru the block then out the thermostat to the rad/heat exchanger or lake depending on the system you have. So in that case the water heater would see the cooled coolant in a closed system if taken from the pump housing.....then for sure there are losses in the hose......just a long heat exchanger to air really.....the way I see it anyhow......

I don't think that's true. The circulation pump would be pulling the coolest water from the radiator or heat exchanger, then pushing that through the system. At the end of that flow, it would go though the engine heat exchanger or water heater before getting back to the circulation pump. The aux water heater lines are actually right at the thermostat in parallel with the engine's heat exchanger when the thermostat is open, and in replace of it when the thermostat is closed. That's why, in an overheating car example, you should run the in-cabin heater on full blast to help cool the car down. That in-car heater is in the same place -hose wise- as the boat's water heater.

And yes, there will be some losses in the hose but once that hose and the compartments it runs through are warmed up, I'd bet those losses wouldn't amount to too much because you have a constant supply of very hot water running through them.

[bud37]

QR_BBPOST So in that case the water heater would see the cooled coolant in a closed system if taken from the pump housing

That is why I worded it that way, yes you are absolutely correct, if the lines are taken from the hot engine discharge they will be as you say.......very poor choice of wording on my part...

You just never know who has done what with those engines...

[tonyiiiafl]

I replaced the high temp switch, thermostat and relief valve. That relief valve was IN there. Lost of muscle. So much I am surprised i didn’t hurt the tank. anyway, couldn’t wit for it to come up to temp, but let it run for 20 minutes. Hot water, not steam. Looking forward to a good test drive this week, to see how long it takes to shut off. The high limit switch I replaced had teh reset button frozen. Maybe that was the problem! Stay Tuned.

[tonyiiiafl]

Test drive A OK! No more water in bilge. I think it was a combo of all three. I got a mixing valve to temper the hot water down to a tolerable temp. Installation next weekend. We are off for a week starting tomorrow when we leave the slip at 7:30AM

[Viper]

Have a great trip Tony. Pics please!

[tonyiiiafl]

For sure. Just cut first day short. Was too much with the 4’ seas beating us up. Should be flat tomorrow afternoon through Sunday. We made it 40 miles though. That was good with me. Wind started howling so sitting tight tied up at a transient slip.