Engine doesn't heat water

[John VerBraken]

I have a '85 H34 and this year for the first time since we have had the boat the engine doesn't heat the water in the water heater.The water heater will heat up with shore power.I replaced the thermostat and no change. After the engine heats up the hoses to the water heater are hot but it must not be circulating the hot water into the water heater.I don't think it is running through the heat exchanger either.Is it the water pump?Thanks for your help.

 

[Joe O]

Run it Hard!

Hi John,I noticed the same with my '83 H34. The AC side gets it hot very fast, but not much on the engine when at anchor. The water does get very hot when I'm motoring along at full power. Yanmar says you have to put a load on the engine to get it hot enough to heat the water. I talked to Seaward, who makes hot water heaters and they said it takes about 1.5hrs to heat the water in their 6 gallon tank, assuming the engine coolant is at 180 degrees. Most marine hot water heaters have just a simple "U" pipe in the tank for a heat exchanger. When I replace my heater, I think I'm going to buy one of those Isomat heaters. They have a coil type loop which has more surface area to transmit heat. I believe that heater would perform much better than what I have now. So for the time being, I wrapped my tank with more insulation and I heat the water with AC before leaving the dock. And, I'll take my shower soonafter shuting the engine down after a long motoring. Hope this helps.Joe

 

[Steve Dion]

Plugged in or plugged up.

John:Do you think that the heater could be plugged up. Also you may have some air in your system. If it is possible, I would try blowing through the pipe from the inlet to the outlet or vis versa just see if there is something in there. Our heater heats the water until it is almost TOOO hot when we motor and at the dock. We just replaced ours after 14+ years because it was starting to weep. Just installed a new Seward S.S.

 

[Clyde Lichtenwalner]

Burp

I'll bet you had the coolant serviced in the main engine recently. Air can get into the long line to the water heater and keep the engine coolant from circulating. Simply disconnect both the water heater feed and return hoses from the engine. Take a garden hose to one side and allow a free stream of water to flush the line. This will work out any air. Without loosing water from the hoses, reconnect to the engine. My engine heats the hot water heater (a boats US replacement - don't remember the name) in about a half hour of running at a 2900 RPM cruising speed. The hot water in the heater will approach 180 degrees F. Very hot. The same circulated water is channeled into a cabin heater. Very satisfactory comfort for early spring and late fall cruising.