Hot water issue

[Jean-Pierre]

Hello !
1992 Carver 28 Raw water cooling. bought boat last fall. I noticed while under way that I had no hot water from faucet, I got hot water while hooked up to 110 v. Verified the STBD engine plumbing, everything looks good. Disconnected the engine hot water return hose out of the hot water tank and started the engine, good water flow, reconnected the hose and started the engine and let run until gauge indicated 150 F. Touched the water hose out of engine going to hot tank but hose is cold..... help
Jean-Pierre

[km1125]

Wonder if it's hooked to the right place on the engine, or is someone put a valve in the return side for winterization.

Are your engines raw or freshwater cooled?

[Phrancus]

is there some thermostat between the engine and the hose to the tank? If there is, it apparently does not open. Take it out and try. If you get warm water to the tank then you know what te replace.

Test it in a pan of water on the stove, it should open up at some temperature that is often stamped into it. But replace anyway, they get slow and die over the years.

[Viper]

You're raw water cooled so no matter where the lines are hooked up, it'll be water doing the heating. The trick is tapping into the right place on the engine if it wasn't done from factory. After the engine warms up, touch the areas where the heater hoses are hooked up to, if they're cold, chances are they're hooked up to the wrong place. If they're hot, something else down the line is wrong. You should also follow the lines and ensure there are no shut-off valves in the lines from the engine to the heater, and make sure the lines haven't been cut and capped off anywhere.

[km1125]

A good kink on one of the lines could stop water from flowing. There's no real pressure in there to overcome a kink. It's just the engine circulation pump that would flow water to/from the water heater and there's other ways to get around it so if there is any resistance in the lines the water will take another route.

[Jean-Pierre]

Did some more fast checking this weekend. no valves, thermostat or kink in lines, all straight lines. I did disconnect the line out of the heater ( from engine ) and splash hot water over me a little..... but when i reconnect the line, it appears the flow stops because the line become almost anbient. I don't like the way this system is designed. very little difference in pressure between engine out and suction side of circulating pump, raw water pump is decreasing that delta ... ?

[km1125]

Really the raw water pump has nothing to do with it. This circuit works just like the heater core circuit in virtually every car manufactured in the last 70 years or more.

If you identified the lines coming to and from the engine, then take the one off the engine that comes BACK from the water heater and see if water comes out that when the engine is running. You can just plug the open port on the motor when you take that hose off. That will tell you if you have circulation from the engine all the way to the water heater and back. If you don't have water coming back, then you've got some blockage there somewhere. If so, you can take both lines off the engine and just hook a loop from one engine port to the other, so you can still use the engine. Then you can try to use some shore water pressure and push backwards through the hoses that go to the water heater. It's possible you have a bunch of crud stuck in the heat exchanger inside the water heater too, so you might be able to flush it out. Once you're sure you have a good flow through there with shore water, then hook back up to the engine.

[bud37]

Source of the post Did some more fast checking this weekend. no valves, thermostat or kink in lines, all straight lines. I did disconnect the line out of the heater ( from engine ) and splash hot water over me a little..... but when i reconnect the line, it appears the flow stops because the line become almost anbient. I don't like the way this system is designed. very little difference in pressure between engine out and suction side of circulating pump, raw water pump is decreasing that delta ... ?

Can you take a pic of how the lines are connected on the engine ?

Just disconnect both lines at the engine and flush water from a hose thru the heater like KM says, you will see immediately what you have or don't have, no need to run the engine.....step one....prove flow thru heater.

[Jean-Pierre]

KM1125
I did exactly that yesterday. I ran the engine at idle until the gauge indicated 150 deg which is my normal temp. I then disconnected the return line from the water tank and CAP the T fitting. HOT ( very ) water came out into the bucket !! good right. I then reconnected the line but with a clear hose which I injected black ink with a syringe.....that ink did not know where to go. so when connected there is almost no flow but when open into a bucket I get good flow. I suspect the circulating pump for now.
Trying to figure out how to put the video of the ink show.
OH ! and another issue, the big rubber exhaust hose were not the same temp. by hand touch, both elbows were the same temp., but I could not leave my hand on one of the rubber hose.

[Jean-Pierre]