Need more hot water

[Scott Lambert]

I have a QSB380 in my pleasure cruiser and often cruise at fairly low power, 1500 to 1800 RPM. Trouble is it takes a long time to heat enough water to have a hot shower. I was considering fitting a 12 volt circulation pump into the coolant line that runs to the hot water system. This would at least get coolant circulating faster through the HWS. Any one see any problems with this?

Topic

[Scott Lambert]

I checked my engine and yep, that connection is there. Trouble is it needs a 1/2 inch NPT (according to Cummins quick serve web site) threaded stub pipe which I am having trouble finding. In the mean time I have fitted a circulation booster pump, photo attached. Gave it a test run today, excellent result. 20 minutes to heat the water even at low revs.

[Scott Lambert]

OK, thanks for that, makes a lot of sense.

[Tony Athens]

I need to update the heater connection pictures on these engines.. Learned this from the truck manuals— it’s way better..

Look at the pic —-All have this location available, cylinder #6—————-QSB 5.9, 6,7, QSC and QSL 9..

Your return is perfect..

Tony

[Scott Lambert]

OK, that all makes sense. Just to confirm I have attached a photo of my engine with an arrow pointing to the correct connection point, (the one marked cabin heater supply on your previous link).
One question, if I tap the coolant off downstream of the pump and return it to the inlet a separate and parallel cooling circuit will be created which sends a portion of the coolant through the HWS and not through the heat exchanger. On a long run once the water in the HWS has heated up this could lead to a slight reduction in cooling capacity. I assume this is not enough to cause a problem?

[Rob Schepis]

Good pics and descriptions. Return is good, supply is not. Needs to come off the block on the exhaust manifold side near the oil cooler. See attached.

https://www.sbmar.com/articles/cabin-heater-connection-ports-for-qsb-6-7-qsb-5-9/

[Scott Lambert]

Connection points

I have attached two photos of the HWS connection points. The first is the supply looking up from underneath and the second is the return looking forward (you can see the back of the alternator). They are the blue hoses and are both connected to the Water Inlet Connection. In the first photo you can just see the return line to the right of the supply line.

[Tony Athens]

Rob called it right——-Let “see” exactly where you are hooking up the hoses.. 99%, that is where the issue is..

FYI, factory hook-up points on the marine engine are that ideal when you want “more”..

Tony

[Scott Lambert]

The water heater is pretty much level with the engine with a hose run of about 5 to 6 feet. I will get some photos next opportunity but basically the HWS hoses come from the water inlet connection, so downstream from the heat exchanger just before the coolant returns to the engine. Obviously this would be the coolest point in the circuit so not a great place to draw the coolant from if you want to heat water.I don’t know if this is normal?

[Rob Schepis]

I would think that should be enough rpms to maintain thermostat opening temperature and adequate flow/pressure from the on-engine coolant pump if the setup is right.

Is your water heater mounted above the height of the engine?

How long is the horizontal run?

Post some good pics of your setup and your current tap points at the coolant loop?

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