Water Heater problem when motoring

[mrousseau]

Our water heater for some reason does not heat when motoring for over 1.5 hours at 2700 RPM.  We looked to see if we had a kink in the lines which we don't.  The marina properly winterized all systems and there is no inversions of the plumbing from the engine to the water tank and back. The heater works very well when plugged to shorepower.  I was wondering if the lake temperature which is actually at 45 degrees farenheit would affect the performance of the heater.  My theory is that if the engine temperature maintains itself between 170 to 180 degrees as it did last summer then my hot water should be approximately the same temperature. 

Although our boat is still under warranty, we would still like to be able to find the problem as we may have to deal with this in the future.  Your input is always appreciated.

Michel and Annick
Lake Champlain

[Ken Juul]

The only things that I can think of are either a blockage in one of the lines preventing flow or an air bubble in the water heater preventing heat transfer.  I would disconnect both water heater lines at the engine.  Pour 50% antifreeze mixture in one line until it comes out the other.  If it backs up and doesn't come out then you have a blockage.  If it takes a while to get flow then you had an air bubble that needed burping.  If it's immediate, then the problem is on the engine side, investigate where the hoses connect for blockage.

[tonywright]

I would suggest opening the bleed for the cooling system. This is located right at the spot where the hose runs to the hot water heater. Run the engine, and wait until coolant starts to come out at the bleed valve. Then shut it off. This removed the air in the system for me. The PO had not done this, and I suspect never had hot water when the engine ran.

Before you do this, make sure coolant is full underneath the radiator cap, and the overflow tank in the lazarette is above the "add" mark.

Hope this helps.

Tony

[Stu Jackson]

Seen this?  :  http://c34.org/bbs/index.php/topic,3769.0.html