Electric raw water pump?

[neelie]

I’m thinking of replacing the belt driven water pump">raw water pump with an electric pump.

Is this a dumb idea? Has anyone done this !

The reason why I’d like to do this is because the belt driven one is all but inaccessible if the engine is hot because I have to lean over the engine to change belt or impeller.

With electric, I can mount it somewhere convenient.

[sailingharry]

A Valiant 50 has a big engine with a lot of water flow. If you want to go down this road, make sure you have a large enough replacement pump. Maybe run the engine in neutral at close to full RPM and time how long it takes to fill a bucket.

[HankOnthewater]

I have installed a small electric water pump on a 4 HP aircooled diesel engine, but that was to cool the exhaust, and lower the temperature of the area. That engine was built-in. Worked very well.
That engine run a large (emergency) bilgepump (engaged by a clutch), a large alternator (with a field disconnect) and a compressor for a hookah (via a clutch again).
I had a temp sender in the exhaust to ensure that I would get a warning, if the temperature was too high.

To do that on the main engine? I guess electric pumps can be nearly as reliable as mechanical ones.
However if the engine stops....... the electric pump might be still going, flooding the exhaust system and then a few cylinders
One would need some system to prevent that happening.

[HankOnthewater]

Hmmm, after reading the post of Sailingharry: the output of a mechanical waterpump is dependant on the RPM of the engine.
An electric pump would have same output across the RPM range. A large electric pump might be nearly filling the exhaust at idle, and a small pump might not offer enough flow at full throttle?
A few things to consider.

[Searles]

Have successfully used composite magnetic drive 12 volt pumps for salt water supply on gen sets up to 10 kva ,the engine thermostat takes care of the coolant temp ,the excitement comes from the oil pressure switch ,so no flow until oil pressure and stops when oil pressure stops ,run for years now ,have not tried this on a main engine but cannot see a problem.⛵️⚓️

[SailingHarmonie]

Originally Posted by HankOnthewater

Hmmm, after reading the post of Sailingharry: the output of a mechanical waterpump is dependant on the RPM of the engine.
An electric pump would have same output across the RPM range. A large electric pump might be nearly filling the exhaust at idle, and a small pump might not offer enough flow at full throttle?
A few things to consider.

This ^^^^.

It can be done with a generator, because they run at constant speed, so the exhaust volume is close to constant. But a drive engine… not so much.

[neelie]

OK.. I agree it’s a dumb idea!

Next question -

Has anyone successfully found a raw water pump which does not use those automatically self destructing rubber impellers?

[Ballsnall]

Originally Posted by neelie

OK.. I agree it’s a dumb idea!

Agreed

Has anyone successfully found a raw water pump which does not use those automatically self destructing rubber impellers?

It sounds like you have a fault with your pump it you are constantly replacing impellers. Several years or 1000 hrs should be achievable. A couple of common issues would be worn pump housing and or bearing, using aged rubber impellers and contaminated cooling water from sand etc.

Solve your problem and you won't need to work on a hot engine

[neelie]

Jeez… no need to be so enthusiastic agreeing with me.

OK… the impellers never get to fail, I change them every year regardless. And even on a cold engine it’s a job for a dwarf contortionist with a universal joint between wrist and elbow.

This is why I got to thinking about arranging a more maintainable solution.

The rubber impeller is the weak link in the chain of engine reliability - bits break off and clog up the heat exchanger, if for any reason the pump body is dry the impeller will self destruct.

[Ballsnall]

Originally Posted by neelie

Jeez… no need to be so enthusiastic agreeing with me.

We like to be supportive on CF 😁

So 2 options I can think of, you could mount the pump in a more accessible location but still belt driven or change the pump to a solid impeller type similar to your coolant pump but it would need to be below the water line as it wouldn't have the same self priming ability.

Your not alone in detesting the maintenance access on raw water pumps. We've all had many a skinned knuckle there.

[Searles]

If the s/w pump is well below the W/L use a belt drive centrifugal self primimg pump ,no more rubber impellers ,or use the globe dry run type ,⚓️⛵️

[SailingHarmonie]

Variable speed centrifugal pumps are not always a great answer here. You need a pump whose flow curve vs rpm gives the engine enough water at all speeds. A typical diesel as an rpm range from 800 to 4000. Not all centrifugal pumps work over a 5-fold rpm range. They also require careful engineering in the plumbing to be sure they can not get air locked, even if below water level. Significant amounts of air can come up even a deep water intake when sailing. With engine plumbing it will be a real challenge to be sure that air can rise past an installed pump.

[SY Harmony]

Originally Posted by neelie

The reason why I’d like to do this is because the belt driven one is all but inaccessible if the engine is hot because I have to lean over the engine to change belt or impeller.

Have you tried laying a blanket on the engine before your body?

[Chris Cringle]

I had a boat with a Volvo MD-2B engine. The Achilles heel on that engine is the raw water pump. It is on the back of the engine and a leak from the weep-hole is not easy to see. But if the inner seal fails, the pump fills the crankcase with sea water in no time flat. After dealing with that situation once, I put a brass plate over the pump aperture and fitted a 12 volt water pump. I measured the flow volume that the engine required at maximum RPM’s and made sure that my new pump could supply at least 150% of that amount. Then I wired the pump to the ignition switch, through a rheostat so that I could match the flow to the requirements of the engine, and through a secondary switch so that I could shut off the water flow should the engine stall. It worked great for years.

[RaymondR]

I used a 12 volt impeller pump to provide water to the exhaust system after I converted to keel cooling.

I wired the pump from the auxiliary terminals of the ignition switch, through the normally closed contacts of a relay and the actuator coil of the relay through the oil warning light.

When the ignition was turned on the pump would be powered however since the oil warning light would be simultaneously be turned on and via the circuit to the coil the normally closed contacts would be pulled open keeping the pump from running.

When the engine started and the rising oil pressure turned the oil warning light off the relay coil would release the relay back to normally closed starting the pump up. If the engine was stopped with the ignition key on the oil warning light would light and the relay pulled to open again and the pump stopped.

It worked well for the couple of years I owned the boat and the engine never got flooded.