Yanmar 3GM(F) Water Heater Performance

[zds]

My Hunter 34 has a Yanmar 3GM(F) that has a coolant loop running thorough a hot water heater. It works relatively poorly.

I recently rebuilt the loop to remove some couplings and shorten the run. Before the rebuild I'd rarely get hot water from running the engine, and the few times I got it were after many hours of motoring (i.e., down the ICW). Since the rebuild I get hot water more reliably, but it still takes more than an hour of motoring to get there.

I'd like to get hot water as fast as the engine heats, which can be done in reverse at anchor. My wife would really like this.

The engine heats up pretty quickly (15 minutes to radiating and untouchable), but the coolant doesn't seem to circulate. I have the lines run from the bypass ports near the pump, but best I can tell coolant doesn't flow until long after the entire system gets really, really, hot.

This doesn't make sense to me. My car has a similar coolant/heater loop setup, and I get heat before the radiator.

Can anyone explain the mechanics of this?

 

[Ron20324]

My brand-new boat had tight turns in the hoses that went from the engine to the water heater, and both hoses were mostly kinked closed. The dealer put in a couple of 45-degree pipe elbows, and that straightened out the hoses and improved water flow.

 

[zds]

Ron-

Is yours a 3GM(F)? If so, how long does it take to get hot water?

I know I got the kinks out of the hoses, but it still seems to take an awfully long time...

Thanks.

 

[Dan Johnson]

ZDS...

I have a 3GM30F in my H34 also. I replaced the hot water heater two seasons ago with a Force 10 (now under a different name). The heater produces VERY hot water (even with its regulator) in about 20 minutes of motoring. You should be able to heat water up to engine water temp once the thermostat opens in a matter of minutes.

What it sounds like is that you need to bleed air out of the hoses between the engine and heater. They come off the engine near the internal pump, but are not in the direct circulation loop through the raw heat exchanger. When you open the lines to install a heater you can easily create a bubble which will block flow once pressurized.

 

[zds]

I've bled the lines a few times, and part of why I rerouted them was to make sure they were bled.

I'm interested in the thermostat comment. Are you sure coolant only circulates after the thermostat opens? I always thought this was a bypass that always circulated. I might have a sticky thermostat...

 

[kloudie1]

3GMF Water Heater

sounds like you have some kind of restriction in the system.. could be a buiild-up at one of the fittings on the engine? Attached is a picture of the top of my engine.. The heater hoses are in the right bottom of the picture . You can see that the hot out to the heater comes off before (under) the thermostat so the water circulates in the heater loop before the thermostat opens, like a car heater .. My heater does not have a tempering valve, and it gets REALLY hot within about 20 minutes, like Dan was saying. If you have a tempering valve, it may be bypassing the flow back to the return line before it goes into the heater. If you have one, the tempering valve should be able to be adjusted to bypass less ?? The second picture shows the water heater hoses going into the heater (the box at left) with no tempering valve. A tempering valve would connect the inlet and outlet, and be adjusted to keep the water from the scalding temperatures that I get ... 160F..

 

[zds]

I'm pretty confident there isn't a restriction either.

I've performed the following maintenance:

-Replace the coolant lines to remove splices
-Re-route the coolant lines to discourage air bubbles and shorten the run
-Flush the system with fresh coolant (using a hand pump - noticed no resistance)
-Bleed the system repeatedly, including while the engine is running (and circulating)

The issue is that it takes a LONG time to circulate hot coolant (which I can verify by feeling the hoses), not that it doesn't circulate. At the same time, the engine gets to operating temperature quickly. So, I feel like I'm missing something...

 

[petersea]

Have you tried to see if there is circulation from the return side of the water heater and if so is it a strong circulation and is it warm ? (take the hose off not the touch test do not do on a "hot" engine)Could the lines be reversed ?? Is the engine circulation water pump working correctly ??? When you say the engine heats up and radiates untouchable in 15 min it could be the circulation pump is bad because while the engine will be hot it won't be "untouchable" if you are talking about he heat exchanger. What I am questioning is you keep saying your engine is getting really really hot, do you have a temperature gauge or a temperature gun it verify the temp ?? (should be about 160/180 hot) The engine warning light will not come on until water temp is closer to 200.Another possibility is the exchanger in the water heater could be "scaled" and needs cleaned (coolant will circulate but will not exchange heat). (circulate a 10% solution of muriatic acid/water with a manual pump to clean... do not put thru engine !) It is also possible the thermostat is not working correctly change it and test. Getting the hot water to heat as quickly as the engine is not realistic as the engine is only about one gallon and the water heater is six gallons and has a smaller exchanger so it will take longer.The car heater is not a fair comparison as it it a water to air exchange and the water heater is a water to water exchange but I agree an hour is a long time.

 

[jibes138]

think how it works

When an engine is started the thermostat is closed and now coolant is circulating. Then the engine gets up to the temperature that the thermostat opens. Immediately the engine is flooded with cold coolant and the same now flows into your water heater. This will cause the thermostat to close again, after a little while it opens again, and the cycle repeats. Without the water heater you have the engine heating up a gallon as my good friend PeterSea mentioned. With the water heater you are removing heat from the coolant and the thermostat will likely take a long time to get to steady state always open. You can observe how long by taking off the cap to the coolant and observe how long before it is in steady state circulation. You'll be surprised how long. The other issue is running at idle, it takes a real long time at idle to heat things up. increase your RPM's a bit to speed things up. You can check you thermostat by removing it and put it in boiling water, it should open right up and close again when removed. If it is stuck open it will take a long time to heat up but if stuck closed you would rapidly overheat your engine and wreck it, you would know if it was stuck closed.

 

[Richard Bryer]

Mine certainly heats up quicker than that, We have hot water after 20 min of motoring. Your hose run looks the same as ours. Sounds like it could only be a thermostat related problem.

 

[kloudie1]

ZDS.. Are the coolant hoses connected to the same places that the ones in my picture are? If the fitting at the thermostat were to be hooked to one of the plugs in the thermostat housing above the thermostat, it would behave kinda like you are describing; low loop circulation and lower temperature. Did ya rod out the engine fittings? Is the water tank free of air bubbles on the fresh side? air pocket over the heatexchanger inside could do that.. Reversed in/out pipes on the fresh side would do that.. Did it always do a slow heat or is it something new?
Just tossing out ideas..

 

[Rick]

Easy check is the thermostat. After reading the thoughts and if I understand your symptoms, it might be the culprit. You dont seem to have anything unusual in your setup. Motoring around at below 75% WOT, or say even harbor speeds of 2000 rpm with not much load on the engine is an easy day for your trusty Yanmar. If the thermostat is stuck open (my theory) the coolant isnt getting up to temp until it overshoots normal. You said the it does ok when the engine gets hot hot. Well once the coolant gets hot and the thermostat is not regulating flow through the cooling circuit, you have an overheat situation about to happen. You could shoot a thermal gun at it to get a read on the temperature. Bottom line, in most systems after about 20 minutes of motoring, the straight hot water should scald you. IF your silly enough to put your hand under it.

Cheers and good luck

 

[zds]

The more I think about it, a stuck open thermostat makes sense.

My engine has an overheat buzzer not a temperature gauge, but I have no reason to believe it's overheating or that there's a problem with the raw water heat exchanger.

I'll take a picture of the engine to show where the water heater coolant lines are hooked up, but if coolant should circulate before the thermostat opens (allowing the water to heat up with the engine), and my thermostat is stuck open, then that would explain my problems.

 

[petersea]

zds,,, not to burst your bubble but with a stuck open thermostat you would have circulation and I doubt your engine would get hot enough in 15 min to be untouchable as you describe. Partly stuck closed maybe but not open, if it was stuck closed you would be overheating. Change it out and see what happens but I'm not sure this is your problem. Test it out as described by jibes138 above. Run the engine with the cap off and verify if there is circulation or not. Why do you think there is no circulation ???

edit to add; when you check the hoses be sure check the ones a the water heater also to make sure they are not reversed there. My other boat had a blead valve at he water heater, as the area is very prone to air locks, so are you sure the coolant system is free of all air locks ???

 

[TropicalPengy]

thermostat is cheap, i would change it anyway after any cooling system repair, also the water pump may be bad, check hoses for sure, bleed any air for sure, but also I would check for scale if you have ever had to add water or coolant, or if you are not the origional owner, there could very well be debris in the system, should also be a small metal plate with holes in it, just after the coolant zincs, you could have zinc deposits blocking water flow as well...

 

[Dan Johnson]

ZDS...

Like Claude, here are pics of my engine front and my water heater connections. The heater hoses are the ones on the right with the red rag around them. Enlarge the picture and you can see where the connections are made at the thermostat housing and water pump areas.

On the water heater, the incoming line is the one connected to the tubular aluminum extension that is the tempering valve that Claude mentioned.

There is a possibility that the hoses are reversed at your heater as Petersea mentioned, and that the incoming flow is being blocked from leaving by a tempering valve if you have one (did you say what heater it is you've installed?). Engine thermostat is apparently functioning if you're getting normal heat at the engine after a short operation cycle.

And, after re-reading your orginal post, there is a strong possibility that you have an obstruction within the water heater's heat exchanger itself--could there be a backflow valve in the heater you have?

 

[shorty]

I have 3GMF on my Pearson 34. New Raritan heater 3-4 years ago. Very hot water in as long as it takes to motor in & set anchor, ~20 minutes as said before. new heater is well insulated so we also have hot water the next morning.

 

[druid]

thermostat is cheap, ..

Careful, we're talking about a Yanmar here. Thermostat for my 2GM20F was $75 (OK, cheap compared to, say, a new engine, but compared to the $10 ones in your car...)

druid

 

[zds]

OK, below are pictures of the connections to the engine.

I'm fairly certain the lower hose that leaves the engine is the hot coolant send, and the upper hose is the return.

Looking at the pictures it seems like they are on opposite sides of the thermostat. That would prevent circulation until the thermostat opens, which must be late considering how long it takes me to get hot water.

Anyone have any suggestions?

 

[rami.gazit]

It takes about 5 minits to get to 85 deg (c) so the thermostat will open and then another 20-30 min to get hot water