Hot water heater question

[prh77]

I have the standard Atwood heater, probably original. I changed the hoses last year, and now it seems to only get warm after extended engine runs. I then changed the thermostat and verified 160 degree operation. I have a valve in the heater feed line - from the freshwater pump fitting - and when I open it, both hose get nice and hot. Also, when I open this valve after the engine is warm, temp guage drops from 160 to 125, then recovers in a minute or so, indicating a transfer of heat. And yes, heater works great on shore power, almost too hot. I do not see how this could be the case, but would direction of coolant flow affect output, ie I reversed the lines?

[Stu Jackson]

Peyton, when you open the valve on the hose from the freshwater side to the heater, does the water get hot?  If it does, then the PO installed the valve, which is NOT OEM and most of us don't have one except for winterization folks, and the valve should be full open to let the freshwater loop heat the domestic water in the heater.  Where in the line is the valve?  Direction of coolant heat will not affect the hot water heater.  See: http://c34.org/bbs/index.php/topic,3769.0.html - discussion further down the thread and on page 2 IIRC.

[prh77]

The valve is in the small hose that comes off the barb on the fresh water pump on the engine. My point is, when you open this valve, both hoses going to and from the heater get hot, but the water in the heater only gets luke warm after extended runs. This valve was in place prior to changing the hoses and worked fine. One added perk of the valve is the engine heats up much quicker with the valve is closed, as you are not heating up that additional loop.

[Craig Illman]

Peyton - To follow on with Stu's comment, it's possible that the PO-installed valve restricts flow in one direction as opposed to the other. I think it's certainly worth a trial to reverse the hoses. Is the valve 3/8" like the hoses off the engine or 5/8" like the hoses off the heater? A 3/8" valve is going to be pretty small inside. You might want to experiment with removing the valve as well.

Craig

[Stu Jackson]

Peyton, please define "extended runs."  It takes almost 45 minutes for our water to get hot and we have a 180 thermostat.  If the valve you have is a simple on off valve, and it's small, Craig could be onto something about a simple restriction in the valve.  There are no valves with handles that are one way valves.  Take the valve off and check if the guts are clear:  look through the valve and make sure it's opening.  What kind of valve is it, gate or ball, or other?  A gate valve requires lots of turns to open it fully, LOTS of turns.  A ball valve is a 90 degree turn.  Tell me what kind of valve it is.  Or/and get us a picture of it.

[prh77]

Its a ball valve. The thing is, the water heated fine last year with the same valve installed...a mystery. I once posted a question about a 180 thermo as opposed to 160. Seems to me 180 would be better for the engine. boiling moisture out of the oil etc. The general consensus at the site was stick with 160. I still wonder if 180 would not be better. The Universal operators manual even says temp range is 165-190.

[Craig Illman]

Peyton - I have a 180 thermostat, like Stu. Puget Sound waters run around 45-55 degrees, although when I was up in BC last summer where the water was in the 70's the engine stayed right at 180. The issue with the higher temperature is that salt precipitates out at temperatures lower than 180. If one runs a higher thermostat, you need to be diligent about maintaining your HX. My opinion is that hotter is better for the diesel, as long as one doesn't overheat it. The standard Kubota thermostat for the engine is 180.

One last thought, kinked or pinched hose somewhere? Did you replace the original hoses with wire-reinforced hoses? I know it's a pretty tight bend where my hoses drop through the engine bed and turn forward.

Craig

[Ken Juul]

The fact that both hoses get warm when you open the valve should indicate that you are getting good flow.  Maybe scale build up on the heating tube in the HW heater is limiting heat transfer.  Maybe it's just the cold ambient air/water temps.  You are starting from much "colder iron" now than last fall.

[Stu Jackson]

Forensics 101

If it was my boat, here's what I'd do:

1.  Take the valve off and see if it's clear inside.  Better yet, remove it unless you need it for winterizing and from your description of its position, it doesn't seem likely.

2.  Check the hoses.

3.  Flush the Atwood heater from the engine coolant side to assure it's not gunked up.  Assure flow by using a garden hose at one end and a bucket or your bilge at the other end.  A 1988 heater may well be past its useful life.

4.  Forget about the thermostat issue, please - it's been beaten to death here for years, and I've used both and they make little difference to heating hot water (except for my comments above about "saving" "hotter" hot water.

5.  Check the coolant level in your manifold.

Before you do all this, run the boat around for awhile at cruising speed.  Take the temperature of the cold water, and every fifteen minutes take the temperature of the hot water, to assure you indeed do have a problem, 'cuz, like I said, it takes well over a half an hour to 45 minutes to get hot water.  I know because we motor 40 to 45 minutes from our slip to sailing territory every time I use the boat.  FWIW, if you leave the electrical heater on for a loooong time the water will get way hot.  If you're comparing this to the engine hot water, you'll be surprised by how different the temperatures can be.

[prh77]

Thank you one and all for the feedback. What a great resource this site is, whitin a few hours of posting to get so much good info. And yes,I took her out today for 45 minutes and got some hot water. I think i was remembering the temp when plugged in, and thinking the engine produced the same scalding temp. Still thinking about the 180 thermostat though....OK will give it a rest.