Another engine related question

[Tim R.]

Another engine related question(hot water)

My heat exchanger is clean but idling(1500 rpms) my engine only gets me warm water. It is warm enough to shower with but not hot. My mixing valve on my water heater is all the way to hot. The engine temp gauge only just registers above 100°F. My water heater is new(Isotemp 6 gal)

I chartered a 2004 Beneteau in the BVIs this year and it seemed to give almost instant hot water. What is different about that system that heats the water so much quicker? Unfortunately the engine temp gauge was busted so I have no idea how hot the coolant was.

 

[sailaway78]

I would guess

I would guess that with the engine just idling, it isn't getting hot enough to heat water. My raw water cooled Yanmar will not get off the cold peg when sitting and idling. Guess the chartered benny had a fresh water cooled engine, which will warm up more and faster than a raw water cooled engine.

 

[Benny]

My guess is it could be a combination of low RPMs and cold raw water temperatures. That cold Maine water could be sucking some serious heat out of that exchanger. Our water temperatures here in Florida are in the 80s, what are yours?

 

[Tim R.]

Last weekend it was kinda warm for this time of season 55°. It can go as high as 65° and I know a couple of swimming holes that get up to the low 70s but I would have to kill you if I told you where they are!

So a 20-30° difference could be the culprit.

 

[Hermit Scott]

How is the slip stream going to the water heater plumbed? The thermostat should hold the water in a loop not letting it go to the heat exchanger and heat the water in your water heater. It could be a sticky thermostat. I have never seen a system like yours in person, but I would think that is how it is arranged.
The external water temperature shouldn't matter. The only thing the hot engine water should have to overcome is the temperature of your holding tank for fresh water.

 

[Tim R.]

Hermit. The raw water cools the fresh water(coolant) at the heat exchanger. The coolant then enters the water heater to heat the water. So if you start off with colder raw water, the coolant will stay cooler and the WH water takes longer to heat.

BTW, this is a very common setup for fresh water cooled engines.

 

[RichH]

How is the slip stream going to the water heater plumbed? The thermostat should hold the water in a loop not letting it go to the heat exchanger and heat the water in your water heater. It could be a sticky thermostat. I have never seen a system like yours in person, but I would think that is how it is arranged.
The external water temperature shouldn't matter. The only thing the hot engine water should have to overcome is the temperature of your holding tank for fresh water.

Many marine engines use a BYPASS thermostat system. The thermostat allows the water to BYPASS in a separate loop until the engine heats to operating temps ... THEN the bypass closes to shunt water INTO the engine. Such a BYPASS system keeps the water pump pressure constant, ensuring longer service life of the impeller. Check the water flow diagrams for your particular engine to see which system you have.

 

[Stu Jackson]

Low heat output at idle

Tim

In our M25 series engines and even in the later M30 and M35 editions, the Universals don't heat up much of the water in the domestic hot water side at engine idle speeds or even 1500 in any reasonably short period of time. The only way I can justify running the engine to make hot water is for battery charging on the second or third morning at anchor. If we "need" hot water we use the stove and our sun shower.

This is not unusual, because we don't want to run our engine at 2000 to 2500 rpm in idle, or with no real load (propulsion) for any length of time. 1500 rpm for battery charging in idle takes about an hour which gets maybe half of the 6 gallons in our DHW heater warm, but certainly not as hot as the forty minutes of cruising speed we use to get to sailing water from our slip.

It's simply a heat transfer issue.

The 1500 watt electric hater in the DHW heater requires a 2000 watt Honda generator, which we have been successfully avoiding.

We don't have any bypass hosing on our DHW side, it's lumbed directly from the FW pump and the thermostat housing.

I have absolutely NO idea what the Beneteau had on it, and instantaneous just doesn't happen with freshwater heated DHW units. Was it propane fired?

Is your engine RW or FW cooled? FW engines run fine with either 160 or 180F thermostats,. RW engines run a lot cooler.

Our electric side heats it up in 15 to 20 minutes, then we turn the electric off. Too many people leave it on unnecessarily.

So, it's still simply a heat transfer issue.

 

[Cpt. Jon]

This is what I love about this site, every time I seem to have a question lingering in my mind, someone asks it for me.

I have a very similar set up, if not pretty much the same in my new-to-me H30. After I got the water pump in, I was really curious about testing the water heater out. I idled it for about 30 minutes and the water wasn't that warm, I think that the engine maybe just wasn't getting hot enough to really heat the water fast. One of these days I'll motor out and remember to test the water temp after motoring for a little bit. I did however plug into the shorepower and test out the electric element not expecting to work and that heated up the water almost instantly it seemed.

I know what I wrote here doesn't help you at all Tim R, sorry , but thanks for posting my question

If I get out this weekend I'll try to motor at higher RPM's and see if it heats the water better.

 

[Tim R.]

Stu, I have the M25xp which I am sure is plumbed the same as yours with the 3" HE. That Bene did not have propane fired hot water and it was probably FW cooled as it was a 42ft. boat. Warmer raw water makes sense. We would idle at 1500 for about an hour to recharge batteries but we would have good hot water after about 15 minutes.

What if the raw water had a bypass so it partially skips the HE and goes right to the Exhaust riser? You could adjust the amount of raw water so that it provides the correct amount of cooling while idling. Maybe link the valve to the shift mechanism so it opens fully when under way.

Not seriously considering this but just brainstorming.

 

[bobtigar]

Re: Another engine related question(hot water)

If it is fresh water cooled, and you have recently drained and refilled the coolant, you may have some air in the system that has created a bubble. Bleed off the air at the highest point in thecooling system. Bob

 

[Lee Coller]

Re: Another engine related question(hot water)

When I bought my Hunter five years ago (new) I had a similar problem, the engine would need to run for at least three hours to get any hot water. The hot water heater had a temperature sensor bypass which the dealer told me frequently failed and they bypassed the temperature sensor (by removing it). No effect, I had the same behavior. I had checked for air pockets in the system, none. Finally after much complaining I finally got them to replace the water heater, and that fixed all the problems.

Later on, examining the one part I had left from the old water heater (the temperature sensor), I notices a lot of calcium buildup inside of it, I suspect what was really happening is that there was a lot of calcium buildup on the heat exchanger on the inside of the tank that acted as an insulator (one thing that we had done was measure the difference in temperature of water entering and leaving the heat exchanger, and difference was much less than expected, just a couple of degrees rather than the 10 or so degrees expected.

Bottom line. You have either:

1) An air bubble in the heat exchanger.
2) A faulty temperature sensor on the water heater (if you in fact have one).
3) Calcium buildup inside the water heater.

 

[Hermit Scott]

Tim-your idea about diverting the raw water should work, but if it's possible I would run the fresh water right after the pump directly to the water heater. That way your freash water doesn't leave the water jacket/water heater area until it's hot enough to open the thermostat. Then it wouldn't matter what temp the raw water is. Maybe that's not possible because it's sealed though. It would seem it is designed to not give any heat to the HX until you don't want any more in the engine and the water heater.
Mainesail sails in maine, I guess. In a recent post he said his water heater temps were border line pushing the limits of the water lines. I think his engine is a 44 westerbake.

 

[Ron20324]

I'd vote that the thermostat is stuck open, not forcing the engine water to heat up very much.

 

[zeehag]

i got rid of my hot water heater as they are a pain in the neck and always leak ....

 

[Mike Holibar]

I'm with Ron, do the easy stuff first and check the thermostat. A common set up on Perkins, Lombardini, and Yanmar engines - your could include many volvos too as they were made by Perkins, is that the calorifier is included in the engine FW cooling circuit, feeding from the discharge side of the FW pump before the thermostat and returning to a valve lower down on the engine block. Only when the engine reaches operating temp, somewhere around 90C should the thermostat open and allow water to circulate through the heat exchanger. My engine, a Perkins M50 reaches Maybe 85C at 1200 rpm no load fairly quickly and the hot water is available after about 30 mins. The fact that your engine is running cold tends to point to a thermostat problem. If there was a fault with the calorifier (say a blockage), then the engine temp would be unaffected - it should still reach temperature. Regards,