recirculating pump

Just wanted to tell all of our experience with adding a recirculating pump to our water heater and fan forced engine fed heater. Without the pump you only get heat once the engine gets really hot and the thermostat opens and the engine is running. With the pump on you get heat within minutes of start up and continue to get heat until the block cools completely (hours). It's a real game changer for $175!

The downside is that it will take longer for the engine to warm up to operating temperature with some of its heat being diverted soon after starting.

No big deal if you are cruising for hours, but could be a problem if you are starting and stopping a lot and particularly if you run the engine out of gear just to heat the boat. The engine may never warm up in that case.

David

Good points but I'm confident in our particular case that the small size of our heater would eliminate the likelihood of the engine being effected in any measurable way.

My engine warms up so fast I almost think there's something wrong w it. Marches right up to 180 degrees in a few minutes and hot water almost that soon. Never gets over 190 and is very stable. Maybe my thin wall casting engine is thin wall to the extreme???

djmarchand said:

The downside is that it will take longer for the engine to warm up to operating temperature with some of its heat being diverted soon after starting.

No big deal if you are cruising for hours, but could be a problem if you are starting and stopping a lot and particularly if you run the engine out of gear just to heat the boat. The engine may never warm up in that case.

David

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To add to this.A diesel engine is a combustion only engine.There is no out side source to fire off the air fuel mixture.The engine it's self needs to warm and retain that heat while running.Running a diesel cooler than it's operating temperature can cause damage.Glow plugs,they are for cold starts and do not operate with the engine running.Some people are unaware of this fact and think they operate like a spark plugs.

With that added.If you're up and running for a while and then shut down for an extended period,I see no reason not to use the system recirculating system.I do agree with David that starting and stopping the engine, while using the system, could possibly reduce engine life and may cause damage over time.

Daddyo said:

Just wanted to tell all of our experience with adding a recirculating pump to our water heater and fan forced engine fed heater. Without the pump you only get heat once the engine gets really hot and the thermostat opens and the engine is running. With the pump on you get heat within minutes of start up and continue to get heat until the block cools completely (hours). It's a real game changer for $175!

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I'm curious to know more. Can you post a link to the product you are talking about?

Certainly,

Heater Circulator Pump 2.5 Gpm 5/8"" Ports 12V

The route of the engines hot water must take into consideration the hot water heater.

To lower temps from the normal 180 F circ water , some will shut down the water flow.

Not great in a series heating circuit!

We had a Webasto diesel/hot water furnace on our last boat and were told not to put an engine heat exchanger for the 4 radiators. At only 50 hp, they said the radiators would take so much heat from the engine that it may never get to 185-190F. The water pump was rated for 7 gpm. On most trawler engines, I'm not sure I see a problem but something to keep in mind. And with Daddyo's 2.5 GPM pump, he probably wouldn't even notice it.

Daddyo: What size engine do you have?

I have twin Lehman 120s.The engine with the heater and water heater runs at exactly the same temp as the other engine. You guys need to realize we are talking about a heater the size of a shoe box. Commercial guys in the north have used the heaters in all of their boats for decades. We had one of the heaters in our last boat and used it for five years. Geez guys these are boats with big heavy engines, be not afraid!

Good discussion. I was wondering if a pump hooked into the closed circuit heat loop off the engine like what's being discussed here, could also be used to circulate coolant through the main heat heat exchanger (sized accordingly to engine) in the event of a water pump belt failure. I'm mean as a temporary emergency procedure in a seaway for a single engine boat where changing the belt would be impractical or impossible. Just a thought. - Steve

SteveH said:

Good discussion. I was wondering if a pump hooked into the closed circuit heat loop off the engine like what's being discussed here, could also be used to circulate coolant through the main heat heat exchanger (sized accordingly to engine) in the event of a water pump belt failure.

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Why not? Most very large engines use separate electrical circ pumps to move jacket water around. They do it in two loops, high temperature (heads and such) and low temperature and nary a fan belt to be found.

This worry about "overcooling" from taking heat off the circ water to use elsewhere is another example of a concern looking for a problem. If someone is seriously bothered and still wants to take advantage of "waste heat" then just put a bypass line around the heat exchanger and divert the "extra" raw water that would otherwise "overcool" the freshwater circuit.

You could even put a thermostatic valve on that line and build a real neat, expensive, and overcomplicated cooling system for no good reason.

If a diesel will start at 30 degrees F then it should run just fine at 175 or even, brrrrrrrrr, 160 or so without self destructing within the lifetime of the boat or its owner.

Yea.., seems like a nice ancillary function that a closed loop recirc pump can provide, as long as you still have a functioning alternator after a water pump belt failure. - Steve