hot water from inverter

[Charles Erwin]

The Universal M25XP is 3 cyl freshwater (antifreeze) cooled motor. Normal operating temperature is 165 -195F. Can you remember why you have this 140F thermostat?

The pump that circulates the antifreeze is a simple automotive non-displacement type pump. Can you manage a detailed pipe and tube diagram? Include particularly the circuit beginning at the motor heat exchanger, the water tank, Red Dot, and return.

Charles

 

[Benny17441]

It is obvious that the equivalent of a heating coil that only produces 6 degrees Fahrenheit of heat is inadequate to heat 6 gallons of water over any reasonable amount of time. Seems to me the size of your unit's heat exchanger is inadequate to transfer enough heat to the water in the tank. You peeked inside the tank at the exchanger, did it seem to be of adequate size and length? Check with the manufacturer about the exchanger specs. If everything seems to be in order then the design of that water heater is not compatible with your cooling system. I agree that it would seem that a water inlet temperature of 140 degrees would be adequate to at least warm water within an hour but with the meager heat transfer available it helps to explain why it does not. Now the downstream water heater seems to be working adequately removing around 37 degrees from its exchanger. This tends to indicate the problem is with the heater's design or fabrication.

 

[Hayden Watson]

The Universal M25XP is 3 cyl freshwater (antifreeze) cooled motor. Normal operating temperature is 165 -195F. Can you remember why you have this 140F thermostat?


Charles

I do not have a 140F thermostat. I have installed 3 brand new 160F thermostats but the engine will not heat above 140F at cruising speed and 2100 rpm. Before you ask, the temperature was checked with the regular temperature gauge and two different non-contact infrared thermometers. all three have been verified for accuracy using a pot of boiling water.

REPEAT, thermostat is 140F but engine WILL NOT heat to above 140F. The highest reading I can get with my infrared thermometers is about 180f on the block near the exhaust.

 

[Hayden Watson]

The Universal M25XP is 3 cyl freshwater (antifreeze) cooled motor. Normal operating temperature is 165 -195F. Can you remember why you have this 140F thermostat?

The pump that circulates the antifreeze is a simple automotive non-displacement type pump. Can you manage a detailed pipe and tube diagram? Include particularly the circuit beginning at the motor heat exchanger, the water tank, Red Dot, and return.

Charles

For background, before I went back to college to become a Structural Engineer, I was a certified large diesel mechanic so I have the basic concepts involved here. As an engineer I have studied thermo and fluid dynamics.

The hot water circuit is completely normal. 3/8" at bypass outlet, convert to 5/8" with straight run of hose to HW-in, HW-out with 5/8" to RedDot-in, RedDot-out with 5/8" back to bypass inlet with transition back to 3/8".

All runs are 100% hose except for the bronze 3/8" - 5/8" transition coupler which is within 12" of engine. The full circuit is free flowing with a flow rate of .5 gallon/minute with a static head of 12". tested by connecting hose to an open bucket held so that the water level was 12" above the outlet hose.

 

[woodster]

I do not have a 140F thermostat. I have installed 3 brand new 160F thermostats but the engine will not heat above 140F at cruising speed and 2100 rpm. Before you ask, the temperature was checked with the regular temperature gauge and two different non-contact infrared thermometers. all three have been verified for accuracy using a pot of boiling water.

REPEAT, thermostat is 140F but engine WILL NOT heat to above 140F. The highest reading I can get with my infrared thermometers is about 180f on the block near the exhaust.

you may want to read this http://forums.sbo.sailboatowners.com/showthread.php?t=130865

 

[Charles Erwin]

Well considering all that then I imagine you will explain to us why you made the heat supply and return to the thermostat bypass circuit instead of the main circuit.

I do not mean sound the least pejorative however it is completely unclear whether your coolant to water heater circuit matches the one Kumma published in their installation manual.

Hence my request for an as-built pipe and tube diagram.

Charles

 

[Hayden Watson]

It is obvious that the equivalent of a heating coil that only produces 6 degrees Fahrenheit of heat is inadequate to heat 6 gallons of water over any reasonable amount of time.

Exactly, this is the biggest mystery.

Seems to me the size of your unit's heat exchanger is inadequate to transfer enough heat to the water in the tank. You peeked inside the tank at the exchanger, did it seem to be of adequate size and length?

I was able to insert the 6mm head of my inspection camera into the tank and see the full exchanger. It is a "C" shaped piece of aluminum pipe that runs from the inlet to the back of the tank then vertically and returns to the front outlet. It is about 30" in total length and probably 5/8"ø. That give nearly 50 square inches of contact surface. In other words is it just like every other Kuuma water heater.

Check with the manufacturer about the exchanger specs. If everything seems to be in order then the design of that water heater is not compatible with your cooling system. QUOTE]

Kuuma says that it should get to engine coolant temperature in about 1 to 1.5 hours. BTW, there is a boat down the dock from me with the exact same model that has the problem of his water being scalding hot after 30-40 minutes.

I agree that it would seem that a water inlet temperature of 140 degrees would be adequate to at least warm water within an hour but with the meager heat transfer available it helps to explain why it does not. Now the downstream water heater seems to be working adequately removing around 37 degrees from its exchanger. This tends to indicate the problem is with the heater's design or fabrication.

I fully agree. I cannot understand how 140º water flowing through a 30" long aluminum pipe immersed in 60º water can loose only 3º. it must be made from some sort of super NON-conductor. I could probably get that much out of a rubber hose!

 

[Hayden Watson]

Well considering all that then I imagine you will explain to us why you made the heat supply and return to the thermostat bypass circuit instead of the main circuit.

I do not mean sound the least pejorative however it is completely unclear whether your coolant to water heater circuit matches the one Kumma published in their installation manual.

Hence my request for an as-built pipe and tube diagram.

Charles

The Bypass circuit method is the recommended way to hook out the hot water heater in most cases. The water in the engine gets hot much quicker than the rest of the cooling circuit so it starts heating before the engine is fully up to temperature. I boat in Puget Sound and our cold water means that the outlet temp from my seawater HX is usually only about 70-80º.

the fact that I have the same temperature at the water heater as at the cooling jacket indicates that the heat is getting to the water heater. it is just not transferring from the coolant to the fresh water in the tank.

 

[Hayden Watson]

The pump that circulates the antifreeze is a simple automotive non-displacement type pump. Can you manage a detailed pipe and tube diagram? Include particularly the circuit beginning at the motor heat exchanger, the water tank, Red Dot, and return.

Charles

here is a link to exactly how my boat is plumbed.
http://www.bing.com/images/search?q...A78E122655C9F23FBEDE3241937C&selectedIndex=19

 

[kloudie1]

I thought this one over a lot over a little sip or two of rum.. Sounds to me that the heat exchanger in the water tank is not fully immersed in the water.. like there is an air bubble keeping the tank from completely filling with potable water. Verify that the inlet is on the bottom and the outlet on top such that the water must fully fill the tank.. Your bore-scope inspection could verify that.. double check that the tank is being used as designed.. that is, make sure that if it is a vertical tank, it is applied vertically and if horizontal, it is mounted in the correct orientation.. The factory may have botched labeling the connections, so if ya can see the water connections, just make sure that they are correct as labeled..
WAter flow in the coolant loop sounds OK 'cause if it were too low, all the temperature would be given up in the water heater.. and the Red Dot in series wouldn't get heat. (no way to bypass the WH to go directly to the Red Dot is what I read, correct? ) No tempering valve on the inlet of the heater that automatically bypasses water to prevent scalding at the faucet?
Engine not coming to temperature could be too much flow in the WH/Red Dot coolant lines, bypassing the thermostat. ya might try putting in a flow restrictor .. a pinch valve maybe.. to decrease flow in that circuit.. I know counterproductive to heating the water, but I believe that is a different problem.

 

[Charles Erwin]

"The Bypass circuit method is the recommended way to hook out the hot water heater in most cases"

Please remember that marine thermostat bypass circuits do not circulate at operating temps.

RTFM is the rule at our shop but whether or not that works for you - I hope you will tell us all what eventually solves the problem.

Charles

 

[joker460]

Just my 2 cents worth. I would take the Cabin heater out of the equation first and see if the water heater will function properly. If you haven't done this already.
It looks like a long run from the motor to the cabin heater then to the water heater and then back to the motor.

 

[Hayden Watson]

I thought this one over a lot over a little sip or two of rum.. Sounds to me that the heat exchanger in the water tank is not fully immersed in the water.. like there is an air bubble keeping the tank from completely filling with potable water. Verify that the inlet is on the bottom and the outlet on top such that the water must fully fill the tank.. Your bore-scope inspection could verify that.. double check that the tank is being used as designed.. that is, make sure that if it is a vertical tank, it is applied vertically and if horizontal, it is mounted in the correct orientation.. The factory may have botched labeling the connections, so if ya can see the water connections, just make sure that they are correct as labeled..
WAter flow in the coolant loop sounds OK 'cause if it were too low, all the temperature would be given up in the water heater.. and the Red Dot in series wouldn't get heat. (no way to bypass the WH to go directly to the Red Dot is what I read, correct? ) No tempering valve on the inlet of the heater that automatically bypasses water to prevent scalding at the faucet?
Engine not coming to temperature could be too much flow in the WH/Red Dot coolant lines, bypassing the thermostat. ya might try putting in a flow restrictor .. a pinch valve maybe.. to decrease flow in that circuit.. I know counterproductive to heating the water, but I believe that is a different problem.

I think I need a BIG sip of rum! Fresh water outlet is above the HX outlet so if water is coming out the tap, the HX is fully covered (check). Kumma does not make a vertical WH (check). No tempering valve (check).

 

[Hayden Watson]

"The Bypass circuit method is the recommended way to hook out the hot water heater in most cases"

Please remember that marine thermostat bypass circuits do not circulate at operating temps.

RTFM is the rule at our shop but whether or not that works for you - I hope you will tell us all what eventually solves the problem.

Charles

My cruising water is only 45-55º so the thermostat is always partially closed to keep temp up. The fact that my RedDot puts out a lot of heat indicates that I have enough available. Remember, the RedDot is after the water heater.

 

[Hayden Watson]

Just my 2 cents worth. I would take the Cabin heater out of the equation first and see if the water heater will function properly. If you haven't done this already.
It looks like a long run from the motor to the cabin heater then to the water heater and then back to the motor.

This will probably be the next thing I try. I am planning to replace all of the hoses and I will temporarily run the new hoses from the engine to the HX and back through the cabin to see if there is any improvement. if that doesn't make an improvement, I may also use some spare hose to put a temporary throttle valve in the main coolant hose from the thermo housing to the water jacket so that I can force more flow through the WH.

 

[Bill Roosa]

Sounds like the water heater heat exchanger may need cleaned on the raw water side. If hot water is present going in and out then the heat exchanger is suspect

 

[IStream]

My guess is that your hot water heater is badly scaled on the potable side, which is inhibiting heat transfer. Have you inspected that side?

 

[IStream]

I swear I didn't see Bill's answer before typing mine but it seems to be the only thing consistent with all the observations.

 

[Hayden Watson]

Sounds like the water heater heat exchanger may need cleaned on the raw water side. If hot water is present going in and out then the heat exchanger is suspect

I used a commercial boiler descaler to clean the inside (fresh water side) of the hot water tank thinking the same thing. I haven't used that product for antifreeze side but will try that. The inspection scope shows the inside clean. Here is the before picture which show a little scale on the pipe. there is now no scale.

 

[kloudie1]

Have ya tried to pop the safety valve lever with water cold but pressured up by the pump? This would burp any gas out of the tank and may let a lot more water touch the heat exchanger tube. Purge with the safety valve until no bubbles come out of the safety outlet.
Something is insulating the potable water from the heat.. might be gas in the tank lowering the level enough to have a bubble over much of the exchanger tube or fouling on the inside or outside of the engine coolant tube .. or not enough flow through the coolant circuit.. Te fact that your thermostat can't hold temperature kinda tells me that ya may have too much bypass flow through the water heater which essentially removes much of the temp control function of the thermostat.... and an air bubble or some bodacious fouling on/in the heat exchanger tube in the heater that is preventing the heat from the engine coolant from getting into the potable water.
Sounds like ya have a good flow in the circuit because the Red Dot is working and the thermostat is not controlling. Strange one.. More rum, please.

EDIT.. too slow at typing.. outer side of the tube looks fine, so that leaves inner side and air bubble.