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Is there an in and out for the coolant hoses to water heater?

3K views 16 replies 10 participants last post by  gamayun 
#1 ·
You'd think this would be a simple Google search or could be easily found in the manual, but it is not. I would really appreciate advice from someone who knows Yanmar engines (3GM30F is mine). I have torn out the leaky water heater and was really very careful to diagram everything....except.....which way the connections were run to the radiator hoses. The water heater specifies an in and an out so I would assume the engine is the same. The engine has one hose coming from behind the water pump and the other off of the heat exchanger. Does it matter which way these hoses flow into or return from the water heater? I feel like it should, but one person I asked said it should not. I assume the flow from the heat exchanger would be the intake to the water heater and the return is toward the water pump side. What is the consensus on here :confused:
 
#5 ·
Generally if something isn't marked like a HWH HtEx, flow can be either way, UNLike the cold in hot out connections. You will need to burp the HtEx lines when you refill the coolant
 
#9 ·
OK - if my reading is correct - you want to know which of the two hoses connected to the engine is in and which is out.

If so, have someone hold or watch those two hoses carefully and start the engine. Be ready to turn if off right away.

Water will spurt out of the 'out hose".

Then - mark it!

Rik
 
#10 · (Edited)
OK, I got the official answer yesterday -- it does not matter which way the hoses go on a Yanmar (or at least the model I have).

If anyone does replace their water heater, I had read that it is important to make sure there is enough coolant to account for the displacement (duh, right?). So I filled it to the top and started up the engine. What I should have done at that point was let it run for a couple of minutes while it burped the bubbles out, turn off the engine, and then check the coolant again. But I let it go and all three alarms went off. Thinking that I HAD added enough coolant so that should not have been the problem, I started checking things like the water intake filter. Just before I took off the pump and belt to check the impellor, I pulled the cap off the heat exchanger and found that the fluid was too low. I added a bit more, ran the engine again under a load, and now I am one step closer to having hot water to clean the dishes :) Lesson learned: check the simple/obvious things first.

Oh, the other thing I did was install valves in the heater lines coming from the engine so if I ever need to work on the water heater, I can isolate those hoses so I don't have to drain the coolant again and I will continue to have a functioning engine while the repairs are being made.
 
#11 ·
For most heat exchangers, in the bottom and out the top is the safe bet in absence of a solid reason contrary. No matter how hard you try to burp the air out, there will always be more leaking in via pump seals and the like, and it will accumulate in HEs that flow downwards, gradually reducing capacity and causing corrosion.

Automotive radiators, for example, generally flow cross/down, BUT there is an air release at the top. Heater cores and engines flow up. Where there is down flow, it is with enough velocity to sweep the air through.
 
#12 ·
Couple of thoughts here. Good if the reservoir is the highest part of the system so everything burbles up instead of locking up in a hose somewhere. If the fresh water gets too hot a 12 v solenoid valve in the line (normaly closed and powered thru engine on and thermostat control strapped on tank. (similar solenoids in dish washers but they're 110.)
 
#13 · (Edited)
Ona marine water heaters heat exchanger, flow direction does not matte. The only time it would matter is if it was specifically factory labeled, and I've never come across one that was. There are perhaps one or two land based indirect fired water heaters (very similar to a marine water heater) that use very specific designs that want to see directional flow.. I have never seen a marine water heater requiring directional flow to the HX...

This is why it does not matter....
 
#16 ·
Here's a generic coolant flow diagram. The water pump is a simple centrifugal type that does not allow contact between the moving part and the stationary housing. The pump pushes coolant into the block around the cylinders, up through the head gasket and into the cylinder head. The coolant circulates like this until the thermostat opens, then the coolant travels through the heat exchanger and loses heat. Back to the pump and around again. In this automotive diagram the radiator is the heat exchanger, on your boat the heat exchanger is, well, the heat exchanger. In this diagram the heater is where you would install the water heater. It won't make and difference which hose on the water heater is connected to which place on the engine, but one place on the engine has to allow coolant to flow into the water pump and the other one has to be connected to the hot water side of the system before the coolant gets to the thermostat. Generally there is a 'water box' area near the thermostat where a hose fitting can be installed.



Best practice would be to install the system so that it would be self-purging, in other words any air trapped in the system would be free to bubble to the highest location.

Source: I have taught these things for about 25 years.
 
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