Raw water pump - how about electric?

[Molteni]

We've recently replaced our inconveniently placed mechanical fuel pump with an electric one . Meant it could be placed in a better position for access.

Our raw water pump is also a real pain to access and it occurred that to replace it with an electric pump would also enable a better place for access and replacing the impellor.

Yet I've never heard of an electric pump being used for pumping raw water through the heat exchanger.

Could it be done?

 

[emmalina]

Can be done but doesn't vary with engine rpm as demand changes always had more success with engine driven centrifugal pumps.

 

[Boater Sam]

Seen it done. There is the doubt concerning reliability, I would want some sort of monitoring on the water flow.

 

[Plum]

We've recently replaced our inconveniently placed mechanical fuel pump with an electric one . Meant it could be placed in a better position for access.

Our raw water pump is also a real pain to access and it occurred that to replace it with an electric pump would also enable a better place for access and replacing the impellor.

Yet I've never heard of an electric pump being used for pumping raw water through the heat exchanger.

Could it be done?

Yes, can be done, but there are several pitfalls: if the pump is not variable speed and therefore pumping constantly at max, then with the engine at idle the exhaust may not be able to clear the volume of water from the waterlock leading to too much back pressure and the engine will stop. Also, if the engine does stop, either for the above reason, or for any other reason, the pump is likely to remain running and within seconds the pump will fill your exhaust with water which will then back up into the exhaust manifold and into one or more of your cylinders. Also, the pump needs to start only when the engine fires, not just you turn the "ignition" switch on. So, you may need a variable speed pump controlled by engine speed and you would definitely need a system to turn off the pump as soon as the engine stops rotating and a system that ensures the pump starts only when the engine fires up and not before.

www.solocoastalsailing.co.uk

 

[vas]

I'll add el.consumption to the previously mentioned reliability and lack of engine speed related output.
Personally think it's a v.bad idea.
I do have a 50euro diesel lift pump replacing the leaking mikuni mechanical one on my yanmar 2GMF generator engine.

 

[Molteni]

Thanks for the replies, it all makes sense now. The pump output must be both engine speed related AND designed specifically for the particular engine.
In theory an electric pump could be matched with, say, the rev counter, but this might introduce another route to catastrophic failure.
Water in the cylinders would be a disaster!

 

[srm]

Water in the cylinders would be a disaster!

Indeed it would. A total engine strip down and rebuild was required when my water cooled manifold corroded letting salt water into the cylinders.

 

[jamie N]

In contrast to the answers above, I've fitted an electric pump to my engine, and am happy with it, although it's a slightly different set-up, in that I converted my engine from raw water cooling to having a closed system using the existing mechanical pump, and using electric diaphragm pumps for the cooling through a heat exchanger.
The issue stated, that having the pump running water into the exhaust at low revs is a real one, but hasn't occurred with my engine when it's been on an extended idle for whatever reason, and TBH, I can't see it happening.
On mine the pump has an on/off switch, which is linked with the alternator to make starting easier: the engine is started, the revs settle down and then the switch for the pump/alternator is engaged, which in turn illuminates a small LED that the pump's got power, plus I've fitted a temp gauge with an alarm onto the exhaust which show's that temp, indicating that the coolant's working.
With my system the engine can turn over as many times as you want without having raw water get into the exhaust, the act of running water to cool the exhaust is a manual operation, as normal as turning on a sea cock. Once the engine has shut down, (believe me) the noise of the electric pump is apparent, and reminds you to switch it off, plus the alternator light's on. All part of a normal operation as it is when one turns the key to isolate the engine panel.
I converted mine to this way as I'd cleaned the cooling passages of the engine, and seen how utterly choked they'd become with crystallised salt.
My mechanical pump is reasonably accessible, and the spares are readily available, so I've no issue with keeping it, but if it were to fail, I've no hesitation about fitting a diaphragm pump in its place.
The system that I installed has now run 35 hours, 12 hours continuously under passage, which aren't that many, but long enough for inherent problems to show themselves in.
For info, the pumps were about £20 each, the little bits of LED stuff are pennies really, and the temp gauge alarm for the exhaust temp was about £2.

 

[emmalina]

Indeed it would. A total engine strip down and rebuild was required when my water cooled manifold corroded letting salt water into the cylinders.

Old Perkins by any chance ?

 

[srm]

Old Perkins by any chance ?

No, marinised BMC 1.5, way back in the 80's.

 

[Fr J Hackett]

My last boat when I bought her was fitted with a aftermarket freshwater cooling system which had an electric pump that failed on the delivery trip, naff said.

 

[QBhoy]

It is commonly done when a auto engine is transplanted into a boat and a marinising attempt has been carried out. Not ideal I’d think, over the conventional and time tested means. But can work. But those I know of, are a constant topic of concern in the back of the owners mind. Flow rate is a concern too…often gotten around or tempered by a speed controller of questionable reliability in a marine environment. Then there is the whole remembering to switch it on after the engine is running and off before it stops, usually…to avoid the risk of pulling water into the oily bits when the engine has no exhaust pressure to keep it out.

 

[jamie N]

Flow rate isn't a concern actually, as the flow rate doesn't change. On mine, there's a pump that takes sea water and pumps it into the exhaust, and a separate pump that takes the sea water and flows it through a small heat exchanger, and then out of the exhaust. There's a thermostat which swaps power to the relevant pump, and is seamless. When the engine's operating at power, the power to each pump is swapped more frequently than when it's idling.
The relay's auto standard (rugged/available/cheap), the thermostat is also 'auto' quality, with the sensor being in the fresh water header tank.
Originally, the engine had a mechanical thermostat, which IS the work of the devil, designed to clog and fail by virtue of its operating temperature with salt water!
The heat exchanger is 22kW, with a thermal shock to the engine coolant being about 5°C depending on which cooling pump is running, with the temperature peaking to 35°C on the exhaust when the 'heat exchanger' pump is operating, otherwise it's at about 19°C when the exhaust cooling only pump is running.
The exhaust temperature alarm is set at 50°C, which then lights up an LED, and gives an audible alarm.
Having warm salt water running through an engine is one that's suitable for the manufacturer, not the user. I'm aware that many engines are already fresh water cooled, but I didn't have that option, as to rig a 2nd mechanical pump for the fresh water engine coolant was far more complicated for me.

 

[emmalina]

Flow rate isn't a concern actually, as the flow rate doesn't change. On mine, there's a pump that takes sea water and pumps it into the exhaust, and a separate pump that takes the sea water and flows it through a small heat exchanger, and then out of the exhaust. There's a thermostat which swaps power to the relevant pump, and is seamless. When the engine's operating at power, the power to each pump is swapped more frequently than when it's idling.
The relay's auto standard (rugged/available/cheap), the thermostat is household quality with the sensor being in the fresh water header tank.
Originally, the engine had a mechanical thermostat, which IS the work of the devil, designed to clog and fail by virtue of its operating temperature with salt water!

If you have a heat exchanger then your engine is fresh water cooled so why would you have a thermostat in the sea water side ?

 

[jamie N]

The thermostat senses the engine/freshwater temperature from the header tank, and switches the seawater pump to the heat exchanger on or off.
One pump is always pumping seawater to either the exhaust, or the heat exchanger & the exhaust, depending on which pump is activated by the thermostat.

 

[emmalina]

Think you mean temperature sensor rather than thermostat ! Still sound complicated What engine ?

 

[jwfrary]

When doing a raw water cooled to fresh water cooled conversion, it would be far better to use an electric pump for the fresh water circulation, in fact you could have it on a timer and continue circulating the coolant for a short time after engine stop, thats what's done on a lot of cars these days.

Johnson pump make an magnetic drive pump specifically for this purpose ans its easy enough to carry a spare.

The raw water pump can then feed the heat exchanger which would then be proportional to the engine rpm and exhaust quantity.

The only. Way to exclude having two pumps is to go for a dry exhaust, not easily achieved in most yachts.

The last remaining issue is to exchange the thermostat for one with a higher temperature value to really get the value from doing this work. That's not always an easy task!

 

[jwfrary]

If you have a heat exchanger then your engine is fresh water cooled so why would you have a thermostat in the sea water side ?

The only time I have come across this is where the gearbox cooler operates on a bypass and has a thermostat in it to allow the oil temperature to come up quicker and also to regulate the temperature. Good idea but something else to go wrong!

 

[jamie N]

Think you mean temperature sensor rather than thermostat ! Still sound complicated What engine ?

Capillary Car Thermostat, TS-120SR Cooling Radiator Fan Temperature Control Switch, Adjustable 0-120°C Heating/Cooling

Brand: HugeAuto
Not complicated, but I've a technical background which helped.
No part of my conversion requires any great level of skill or special tools, and is a lot simpler than having to strip the engine down to clean the cooling passages.
The engine is a Ruggerini RM90, single cylinder 9.4hp.

 

[emmalina]

Capillary Car Thermostat, TS-120SR Cooling Radiator Fan Temperature Control Switch, Adjustable 0-120°C Heating/Cooling

Brand: HugeAuto
Not complicated, but I've a technical background which helped.
No part of my conversion requires any great level of skill or special tools, and is a lot simpler than having to strip the engine down to clean the cooling passages.
The engine is a Ruggerini RM90, single cylinder 9.4hp.

OK if it works for you just seems to over complicate a tried and functional system. I have just converted my Mani cooler to coolant rather than sea water as corrosion will eventually kill it. But pumping water through you hx and then into your exhaust elbow is standard and simple as for thermostat longevity mine is 42 years old and works fine ! I do go with the KISS mentality. The fuel pump mod I could go with especially when its time to bleed and I have had diaphragm pumps fail and put fuel into the oil.