Another water heater problem

[Camndon]

My 6 gallon Raritan water heater has worked fine for years. I just renewed the heating element and magnesium anode. The water heats normally on shore power and seemed to work well off engine heat at first, but now doesn't heat from the engine (Perkins 4-108). After running the engine at cruise power for an hour, with temp normal at 170 degrees and coolant level normal, I get about two quarts of warm water before it goes cold--never the normal "hot' level. What should I do next?

[makomark]

Does the HWH have shutoff valves in the hoses from the engine??? Are they open?? If not that simple....I would suspect the heat exchanger inside the HWH is clogged or scaled over...when was the last time the engine cooling system was flushed? An IR temperature gun can be used to check the coolant's circulation...

[Camndon]

Nope--no shutoff valves in the hoses. I would have suspected the heat exchanger inside the Raritan, except for the fact that I have a diesel-fired hydronic heater plumbed into the engine coolant lines and, using it alone, it heats the Raritan like it always has for the last 12 years. A diesel mechanic and I troubleshot the system yesterday and verified that the engine thermostat is working, the coolant lines all heat up like they should and the coolant line to the overflow tank heats up. It may be that there is a restriction near (or in) the Raritan that is overcome by the two in-line water pumps that are part of the hydronic heat system--whereas the engine pump alone won't do it. So--I'm going to try running the engine until the lines are hot, confirming that I'm not getting hot water at the tap, and then turning on the hydronic heater (air only, no furnace function, which turns on the two pumps) and see if that allows the Raritan to heat up.... Let you know.

[Camndon]

Looks as if the problem is with the engine pump. Ran the engine under load for 30 minutes (engine temp showed 170 degrees) without any noticeable hot water from the tap. Turned on the hydronic heater--two in-line water pumps (no furnace)--and got very hot water from the tap within about 10 minutes. Water pump was new about six years ago (approx. 300 engine hours).

[RicardoMarine]

The engine coolant supply (to the WH) must come from upstream of the engine thermostat.
This creates a mild coolant pressure caused by the circulating pump that is constantly charging the engine block with coolant.

The engine coolant return (from the WH) must feed into the engine circ pump suction side.
This allows for taking advantage of the pressure differential between the two sides.
No pressure differential..... and you'll have insufficient coolant flow to/from the WH.


Also, and perhaps a long shot..... your WH outlet (supply) must be taken from the port that leads into the upper portion of the WH tank.
Cold water enters the lower section only.
If these were reversed, it may cause your limited amount of warm/hot water.

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