Impeller cooling.

[jamie N]

A fair number of threads on here involve the above. On a car forum, it's rare that the water pump gets a mention, so why do 'we' tolerate these little rotating rings of rubbery crap?
My Toyota Hybrid has an "Inverter Pump" for circulating cooling fluid around the inverter, and cooling it. This pump is lifed at about125,000 miles, which is about 4,000 hours of operation; a substantial number of 'yottie' seasons.
The pump will cost about £25.00, and it requires 12VDC and about 2A whilst running. On any boat the rubber impeller is far more likely to stuff itself than an alternator, so having electrical power from the engine is a better bet than having rubber impeller cooling to it.
To get a specific Volvo/Jabsco impeller won't be as simple to get as it is a Toyota Hybrid spare, anywhere in the World.
On my boat the engine still has an impeller to circulate the coolant around the block, but the cooling of this through a heat exchanger is electric. When the impeller dies, I'll replace it with the Toyota pump, which is maintenance free for the rest of the life of the engine/owner.
The impeller pump on my engine has pipes to and from it, so bypassing to an electric pump is simple, but I'd imagine that some engines have the pump 'within' the engine, which is a different problem.
Tell me where it's wrong to do this without stating "the manufacturer designed it like this", or that "it's always been done like this"?
Car manufacturers design stuff to last 1,000's of hours, cheaply and in more robust conditions than a yacht engine is exposed to, for years of service.
We're being duped..................

 

[Sandy]

What sorts of volumes of salt water, salt water with stuff in suspension does if move per hour?

 

[jamie N]

1200 litres of coolant per hour, 20 l/m. The impeller on my engine is only dealing with freshwater/coolant. The raw water to my heat exchanger is by diaphragm pumps, but 'when' they go down, I'll happily replace them with the above.

 

[QBhoy]

I’d say the there is usually a huge difference in circumstances between the marine environment and the frequent and less stressed auto environment. The more mechanically driven or oriented parts than electrically dependant parts in the marine environment, the better perhaps.
I’ve always been astounded by the failure rate of some engines that are considered bombproof in the auto world, but when placed in the marine world…just don’t last.
Cars get frequent use and usually sit in a more stable environment. Marine engines in a boat (and their ancillary parts) need to deal with infrequent use, high loaded use, salt water exposed, hugely variable humidity and temperature conditions.Only the tried and tested usually have success in such a world.

 

[Boater Sam]

The rubber impeller pimp is a positive displacement pump. I suspect , maybe wrongly, that the inverter cooling pump is only a circulator type pump and will therefore not self prime. Could this be a problem?

 

[Sandy]

1200 litres of coolant per hour, 20 l/m. The impeller on my engine is only dealing with freshwater/coolant. The raw water to my heat exchanger is by diaphragm pumps, but 'when' they go down, I'll happily replace them with the above.

It will be interesting to hear how long the replacement lasts.

 

[oldgit]

Yanmar 230Hp. Quote 2000 hours before changing the impellor.
Capacity. 6000 L/Hr.
Might risk 200 -300 hours before changing.

 

[geem]

I have only changed my Perkins impeller twice in 10 years. Done about 2000 hrs

 

[jamie N]

The rubber impeller pimp is a positive displacement pump. I suspect , maybe wrongly, that the inverter cooling pump is only a circulator type pump and will therefore not self prime. Could this be a problem?

The inverter pump will be replacing the impeller pump, which is sited about 1/3rd of the way 'down' the engine, thus there's a head of water above it which will negate the need for priming.
With the pump being magnetically coupled, there's not a seal to wear either.

Yanmar 230Hp. Quote 2000 hours before changing the impellor.
Capacity. 6000 L/Hr.
Might risk 200 -300 hours before changing.

That'd be £30 a year, or as the Aberdonian in me would think, 10p an hour wearing itself out!

 

[alancollins]

I replace mine on alternate years, say every 120/150 hours. Why take the risk for such a small cost saving. It's why I use Volvo service parts rather than pattern ones. As a mechanic said to me "why risk a £20000 engine in order to save a few pounds?"

 

[PCUK]

Never heard o

1200 litres of coolant per hour, 20 l/m. The impeller on my engine is only dealing with freshwater/coolant. The raw water to my heat exchanger is by diaphragm pumps, but 'when' they go down, I'll happily replace them with the above.

I have not heard of your system before. Can you put up some pics to show the diaphragm pumps please?

 

[vyv_cox]

The inverter pump will be replacing the impeller pump, which is sited about 1/3rd of the way 'down' the engine, thus there's a head of water above it which will negate the need for priming.
With the pump being magnetically coupled, there's not a seal to wear either.

I don't think I am understanding your terminology. As has been said, the raw water pump is a positive displacement type that can 'suck' water from outside the boat even if the suction pipe is empty. I cannot understand how it can be 1/3 of the way down the engine unless I am totally confused.

 

[jamie N]

Unfortunately I'm unable to 'draw' on the photo, however the impeller water pump is situated at 2 O'Clock from the left hand engine mount, and 5 O'Clock from the alternator. Directly attached to its right is the fuel pump with the pipes going up to the fuel filter. The engine's a Ruggerini RM90.
The water pump here has the black inlet pipe cut off, this can be (nearly) seen 1/2 way between the 2 engine mounts. From the upper side of the pump, the pipe goes up to the dreadful piece of crap that was the thermostat/exhaust monstrosity.
On the boat the top of the engine is 'about' at water level. As I've converted the engine to fresh water cooling, this part of the cooling is a closed loop through a heat exchanger. The diaphragm pumps feed the raw water side of the engine. When this impeller fails, or does another year, I'll replace it with the aforementioned Toyota unit for £25.00.

 

[jamie N]

Never heard o

I have not heard of your system before. Can you put up some pics to show the diaphragm pumps please?

Unfortunately, I've no pictures of the system installed, so again I hope that the written word suffices
This is a 12VDC 4-5 l/minute diaphragm pump. From the raw water seacock to the inline filter, to a 'Y' piece, where one hose goes to the 1st diaphragm pump which pumps exclusively to the exhaust in the traditional manner. The second hose to the 2nd diaphragm pump, which pumps to the heat exchanger, and out through the exhaust again. Which pump is running is controlled by a capilliary thermostat, where the relevant pump is energised as per the engine temperature. The engine 'impeller' is circulating water all of the time through the hot side of the heat exchanger. The 2nd pump is energised for a few seconds a minute to keep the engine at a good temp when it's running flat out. The engine cooling water isn't under pressure, and has a header tank from a Ford Fiesta, which is where the temperature probe is fitted to sense in order for the capilliary relay to function.
If either diaphragm fails, it's a very simple action to swap hoses to get the engine running again, albeit with full time cooling.
It's a very simple and robust system, that didn't require huge technical skill to fit. For me anything is better than raw water cooling, and to have a mechanical thermostat with salt water is a lesson in how to choke an engine cooling system.

 

[wingcommander]

Unfortunately, I've no pictures of the system installed, so again I hope that the written word suffices
This is a 12VDC 4-5 l/minute diaphragm pump. From the raw water seacock to the inline filter, to a 'Y' piece, where one hose goes to the 1st diaphragm pump which pumps exclusively to the exhaust in the traditional manner. The second hose to the 2nd diaphragm pump, which pumps to the heat exchanger, and out through the exhaust again. Which pump is running is controlled by a capilliary thermostat, where the relevant pump is energised as per the engine temperature. The engine 'impeller' is circulating water all of the time through the hot side of the heat exchanger. The 2nd pump is energised for a few seconds a minute to keep the engine at a good temp when it's running flat out. The engine cooling water isn't under pressure, and has a header tank from a Ford Fiesta, which is where the temperature probe is fitted to sense in order for the capilliary relay to function.
If either diaphragm fails, it's a very simple action to swap hoses to get the engine running again, albeit with full time cooling.
It's a very simple and robust system, that didn't require huge technical skill to fit. For me anything is better than raw water cooling, and to have a mechanical thermostat with salt water is a lesson in how to choke an engine cooling system.
View attachment 149747

Surely this type of pump is designed for intermittent demand like turning a tap on and off.

 

[PCUK]

To further clarify, the raw water from the sea comes into the first in-line pump after the inlet sea cock. What type of pump is that?
Is this the water pump?

 

[jamie N]

Surely this type of pump is designed for intermittent demand like turning a tap on and off.

Not quite, they do have limited running time when operating at pressure and drawing amps, but are rated for continuous running without resistance, such as going directly through a heat exchanger where there's minimal backpressure. This graph is from a 'bigger' unit, but the idea's the same. After several hours running the surface temps of mine are ambient to the boat; cool.

To further clarify, the raw water from the sea comes into the first in-line pump after the inlet sea cock. What type of pump is that?
Is this the water pump?

View attachment 149753

Yes it is, that's the impeller pump that I'm going to replace with one from a Toyota, it's easy to do as the pump illustrated by the arrow has hoses to and from it, thus when it dies, I'll remove the old impeller, redirect the hoses to the new pump, and wire it up. The old pump, as it's got a shaft, will be blocked off with a blank and a separate water hose to it, in order to keep it filled with fluid in case the drive shaft requires cooling, as per the original spec.
I'm in awe of your interpretative ability and being able to draw a line for me! Cheers!

 

[PCUK]

Only basic Photoshop, but useful sometimes. Unfortunately the problem with your proposed system is that the impeller pump runs at variable speeds to match the enigne speed, thus pumping more water through the system at higher revs when the engine is producing more heat and therefore providing a greater cooling medium. With a constant running pump the engine will overheat at higher revs unless the pump is rated to the maximum that the impeller pump can produce.

 

[jamie N]

It's not a proposed system, the system is built and has been running reliably all summer, albeit only for 40-50 hours due to a mast breakage.
The only item not fitted is the replacement for the impeller, which will be the Toyota inverter pump, which is 20l/min. Without knowing the precise amount of flow that the present rubber impeller pump flows, I'll bet that it's not a litre every 3 seconds, so the Toyota pump will be circulating water at a faster rate, through the heat exchanger which is a 22kW item, it cools surprisingly quickly with 'that' pump running far less frequently than the 'other' pump.

 

[vyv_cox]

Surely this type of pump is designed for intermittent demand like turning a tap on and off.

Very true. My water cooled fridge is pumped by a Jabsco Par Max 1 diaphragm pump running on 6 volts via a voltage reducer. I asked Jabsco for their advice and was told I could expect 10,000 hours.

The reality is that the plastic cam wears out in less than half that. They are not designed for long term running.