More than a year ago after I was horrified at the cost of new heat exchanger and plumbing for my fresh water cooled Volvo Penta 2003 I converted it to raw water cooled with anode. Only to find many VP 2003 already were raw water cooled. The modification was a vast improvement. Got rid of leaking plumbing, cheaper, more HP and simpler.
Next question. It needs a new raw water pump for $400. I replaced bits of it a few times now and its leaky and wobbly.
A good same volume positive displacement 12V pump is $70. Is there any reason I dont know about for not getting rid of the old raw water pump and going electric?
A mechanical driven pump will provide a variable amount of water in proportion to engine rpm. Engine exhaust ( in a wet system) clears the used water in proportion to engine rpm.
Low rpm =low exhaust+low water supply.
High rpm=high exhaust+higher water supply.
An electric pump with a basic set up will provide the same volume of water throughout the entire rev range of the engine.
I would want to be sure if using an electric pump, that at low engine rpm that the exhaust can clear the water without pressure choking or completely flooding the system, it may or may not be a problem but you should be mindful of this when looking down this path.
Good point Jolene.
RE:Is there any reason I dont know about for not getting rid of the old raw water pump and going electric?
Here is something to consider.
Larger engines in ships have cooling water supplied by electrically driven centrifugal pumps.
These run at a constant speed/ delivery rate, but don't exit via exhaust.
With a "positive displacement"pump you could be supplying cooling water at a higher pressure than your standard pump.
This could lead to the coolant water being forced between the head gasket/head/ crankcase joint.
As the piston is on the downstroke the vacuum in the cylinder combined with the extra pressure could draw water into the cylinder.
For this reason I think a 12V centrifugal pump would be a safer choice. Maybe two pumps in parallel with valve to quickly engage a backup pump. ( large ship system)
Of course you would have to wire in an alarm and fail safe system.
I would give it a try at least.
Sounds like a fun project.
gary
If you go electric it would be best to toss the thermostat and use a water pump controller similar to the Craig Davies unit.
daviescraig.com.au/product/electric-water-pump-fan-digital-controller-kit-8002?srsltid=AfmBOorIYikdKw5EaSisN0nPTCGyr-ran5P4kEtNzIW5o19M5Hg1eXCO
These are expensive and you still have to add the waterpump! They turn the pump on and off as required.
If the shaft of your mechanical pump is still OK I would go to your nearest engineering shop and buy a new set of seals and sealed bearings. If the pump has open race ball bearings, replace them with sealed units. The pump the manufacturer provided will be the best but check the rebuild instructions they don't always get this right and have the seals arse about.
Thanks for suggestions.
I already did toss the thermostat Ramona. I found with the new raw water cooling the engine runs very slightly warm. Its probably not as efficient as making it run at 90DegC but I like the lack of heat and getting rid of a moving part (thermostat).
Ive got a temperature sensor in the cooling water output from the block which shows a rise of maybe 5 Deg C in the water even after running the motor at cruising speed for an hour.
My plan was to make the electric pump run at the same litres per minute the engine would pump going flat out. So at low engine revs the flow rate would be too high but flat out it would be OK. But it could clog the exhaust with water which Jolene mentioned. Need to check that.
Its a very easy thing to implement so I think I will try it.
Select to expand quoteTrek said..
More than a year ago after I was horrified at the cost of new heat exchanger and plumbing for my fresh water cooled Volvo Penta 2003 I converted it to raw water cooled with anode. Only to find many VP 2003 already were raw water cooled. The modification was a vast improvement. Got rid of leaking plumbing, cheaper, more HP and simpler.
Next question. It needs a new raw water pump for $400. I replaced bits of it a few times now and its leaky and wobbly.
A good same volume positive displacement 12V pump is $70. Is there any reason I dont know about for not getting rid of the old raw water pump and going electric?
You would need some kind of regulator which reads engine rpm, more rpm, more water and other way around. Not sure if or how this can be obtain but maybe some electrical genius know how ( probably would install on my boat if possible ).
IMHO rebuilding the mechanical impeller pump would be a superior job, for sooo many reasons ...
Select to expand quoteKryspen said..Trek said..
More than a year ago after I was horrified at the cost of new heat exchanger and plumbing for my fresh water cooled Volvo Penta 2003 I converted it to raw water cooled with anode. Only to find many VP 2003 already were raw water cooled. The modification was a vast improvement. Got rid of leaking plumbing, cheaper, more HP and simpler.
Next question. It needs a new raw water pump for $400. I replaced bits of it a few times now and its leaky and wobbly.
A good same volume positive displacement 12V pump is $70. Is there any reason I dont know about for not getting rid of the old raw water pump and going electric?
You would need some kind of regulator which reads engine rpm, more rpm, more water and other way around. Not sure if or how this can be obtain but maybe some electrical genius know how ( probably would install on my boat if possible ).
Off-the-shelf items like the Davis Craig I mentioned above do exactly that. It's a computer that you set the temperature required, and that's it. It's very expensive, though, and fixing the original pump would be best. I use one in my race car, and my yacht has a rebuilt original.
I don't think the temp control would be a good option for raw water flow control in a wet exhaust
It would be fine in a closed cooling system for which they are designed .
For example you can still have a hot engine brought to a low idle.
Flow control for an electric pump should ideally be controlled via engine rpm either electronically or mechanically. But I guess it all gets back to whether water flow is an issue .
Rebuild or new and install a thermostat for a raw water-cooled engine. They are a lot colder. I think my old Volvo thermostat was 55 or 60 degrees. The bits to rebuild my Johnson FB4 were well under 50 dollars from an engineering shop.
There will be an equilivient of Brittons Pumps somewhere near you
Otherwise post it to them.
Select to expand quotewoko said..
IMHO rebuilding the mechanical impeller pump would be a superior job, for sooo many reasons ...
Absolutely. Try Partsforengines for rebuild kit.
Select to expand quotewoko said..
IMHO rebuilding the mechanical impeller pump would be a superior job, for sooo many reasons ...
Absolutely. Try Partsforengines for rebuild kit.Select to expand quoteTrek said..
Thanks for suggestions.
I already did toss the thermostat Ramona. I found with the new raw water cooling the engine runs very slightly warm. Its probably not as efficient as making it run at 90DegC but I like the lack of heat and getting rid of a moving part (thermostat).
Ive got a temperature sensor in the cooling water output from the block which shows a rise of maybe 5 Deg C in the water even after running the motor at cruising speed for an hour.
My plan was to make the electric pump run at the same litres per minute the engine would pump going flat out. So at low engine revs the flow rate would be too high but flat out it would be OK. But it could clog the exhaust with water which Jolene mentioned. Need to check that.
Its a very easy thing to implement so I think I will try it.
Running at design temperature is important for thermal efficiency and minimising cylinder corrosion. Buy a thermostat when you get the water pump kit.
I hate to place a dampener on that theory ....
Quote "It was found that when the temperature increases by 10??C, the dissolution of the iron-carbon alloy accelerates by an average of 2.3 times"
Read here:
www.sciencedirect.com/science/article/abs/pii/S2214785320359575
In theory the engine running much cooler is better for it that's a reason I like the idea..
BUT!! the diesel does burn less efficiently. The design problem is making the flow rate of the cooling water match the engine RPM.
Any engine that was set up to be raw water cooled was fitted with a lower temp thermostat than it's fresh water counterpart. 
My engine is keel cooled but has a belt driven Fynspray pump for the exhaust, I was thinking of electric pump and having an electric engine speed controller mechanically tied into the engine throttle control itself, the ones I've seen have a dial but a lever type like on a remote control car could probably be found that could deal with higher amps
Select to expand quoteTrek said..
I hate to place a dampener on that theory ....
Quote "It was found that when the temperature increases by 10??C, the dissolution of the iron-carbon alloy accelerates by an average of 2.3 times"
Read here:
www.sciencedirect.com/science/article/abs/pii/S2214785320359575
In theory the engine running much cooler is better for it that's a reason I like the idea..
BUT!! the diesel does burn less efficiently. The design problem is making the flow rate of the cooling water match the engine RPM.
That's why the engine manufacturer's method is best. They spend ship loads of money developing cooling systems. I would use the thermostat and pump the manufacturer used on the raw water version of your engine. The "rubber" impeller blades will fold down on the shaft when the thermostat is closed, when open the the pump will pump the right amount of seawater. If the pump overspeeds the blades will fold down but the manufacturer would have sized everything for you.
There is a bypass hole or passage past the thermostat so some water will always circulate.
Select to expand quoteUncleBob said..
Any engine that was set up to be raw water cooled was fitted with a lower temp thermostat than its fresh water counterpart.
That's an interesting observation, perhaps an allowance for organic build up.
Select to expand quoteTrek said..
I hate to place a dampener on that theory ....
Quote "It was found that when the temperature increases by 10??C, the dissolution of the iron-carbon alloy accelerates by an average of 2.3 times"
Read here:
www.sciencedirect.com/science/article/abs/pii/S2214785320359575
In theory the engine running much cooler is better for it that's a reason I like the idea..
BUT!! the diesel does burn less efficiently. The design problem is making the flow rate of the cooling water match the engine RPM.
Engine temp also has metallurgical considerations, ie; the piston will expand a given amount at a particular temperature, causing the rings to work most effectively. Too hot too tight = bad too cold too loose burn oil glaze cylinder = bad
