Replacing belt driven seawater pump with electric one

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peterbringloe

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My 55 hp marinised Nissan has a belt driven water pump. It has a 6" pully wheel. I am now on my third pump (it's a Sherwood because I couldn't get the original Jabsco). It's location makes it difficult to fit and to adjust. It has a 1" inlet and outlet and puts out a prodigious amount of water. The Vetus swan neck bulges dangerously with each pulse.

I've heard that some BMW and Mercedes cars now have electric water pumps. Are there any reasons why a suitable electric pump couldn't be fitted - if there is such a thing for sea water?

Any comments appreciated.
 
Or you can use one of these which are available from ASAP Supplies.

Not cheap, but excellent and designed to run 24/7. Magnetic driven impellers so no seals to go wrong. I've used them for my hot water system for more than 15 years, though the earlier ones had shaft driven impellers which required the seals changing once every five or so years. /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 
The belt driven pump runs at a speed proportional to engine revs, and stops when the engine does. The danger with an electric pump is that it could pump water into a stopped engine or one that failed to start immediately, via the exhaust valves, with disastrous results.
 
I think they are only suitable for circulating the antifreeze. In indirect cooling the seawater goes into the exhaust elbow after it leaves the heat exchanger, and that is what presents the danger of pumping water into the cylinders if the exhaust outlet or any part of the exhaust system is as high or higher than the cylinder head. This needs to be considered at all possible angles of heel.
 
>>The danger with an electric pump is that it could pump water into a stopped engine or one that failed to start immediately, via the exhaust valves, with disastrous results. <<

Actually not so. You simply wire it, as I have, to your ignition switch!! Turn engine off - turns pump off!

I take your point re an engine not starting within a reasonable period, but the same risk occurs with a 'normal' pump too. OR, you could again do as I have done, and have the pump wired through it's own circuit breaker so that a simple 'Press' will turn it off even with the ignition switch on.

All pretty straightforward I think.
 
Thanks very much everyone. Very encouraging. Just one question - the point about a mechanical or belt driven pump running faster or slower according to engine speed. Could this be a problem?
 
provided you have sufficient flow to cope with engine heat output at max power, I dont think so.

there still is a risk of engine damage in situations where the engine is stopped mechanically but the pump stays on - like rope round prop or fuel blockage. you will have to remember to switch off but the oil pressure alarm should remind you.
 
A simple solution would be to run the pump via a relay operated from the W terminal of the alternator via diode,. This only provides power when the alternator is working. Although that would mean an overheated engine if the alternator or belt failed. Either way you would need an overheat alarm.
olewill
 
If the pump is rated to supply sufficient water to cool the engine at full load, won't it be pumping too much water for the heat output at lower speeds/loadings?
 
How many marine engine manufacturers use an electric pump for raw water circulation?

I cant think of any, maybe there's a reason for this? Think about it some more. You may discover that reason.
I would just ensure that the pump that was originally fitted is in good condition.

You dont say WHY you are on your third pump, something may be wrong somewhere else.
I have had Jabsco type pumps on engines for 30 yeqars and have never had one fail completely, unless it was an impellor failure.

More info and thought required.
 
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