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MG MGA - Electric Water Pump

Still plodding on with my digitising of old Safety Fast magazine technical articles for the MGCC.

I came across an interesting article on cooling MG race and road cars. The articles zeroes in on MGB and MGF cooling using electric water pumps. The pumps are supposedly more efficient than our mechanical pumps. Also they allow removal of the mechanical pump (or at least the impellor), freeing up a bit more HP or perhaps causing less heating. As we share the B-Series engine with the MGB I guess the article could be also read across to the MGA.

The UK supplier of the pump and accessories is and more specifically:

They are the UK distributor for an Australian company that makes the pumps: (Davies, Craig).

I pass the information on to you all for information and discussion.

Steve Gyles

I emailed the company and this was the response:

"We have sold quite a lot of EWP80 pumps to classic car owners over the years, including a couple of MGAs, but I know there's very little room to install the pump. Sadly we've stopped selling car-specific kits (for now at least) as most owners seem to want to do their own thing!

The best place to install the pump is in the bottom hose, supported by the hose.

The pump can be operated in several modes: as the only pump, driven by a variable speed electronic controller; or as a secondary pump, when it can be controlled either by a manual switch or an automatic temperature switch set to turn it on when the coolant reaches a preset temp level, exactly as with an electric cooling fan. In any of these modes, it is a good idea to wire the pump so that it can keep running for a couple of minutes after engine shutdown, to prevent any heat soak problems. If your existing mechanical pump is ok, then we'd recommend using the EWP80 as a secondary pump, controlled by an automatic switch.

The total cost depends on which way you choose to go, but the main part of the cost is the EWP80, which is 155.20 including vat."

Steve Gyles

I wonder how the pump can prevent heat soak problems. That statement seems to assume that an electric fan is also running at the same time the pump is. And if it is, think about all of the current draw while the engine is not running.
JM Morris

Steve, The Davies, Craig pump has been available in Australia for a number of years now. I decided to wait until my existing pump needed attention before fitting one.

JM, as I understand, the system can run indepentently for a few minutes after shut-down.

Anyone fitted one yet?

Barry Gannon

I've read of several people having reliability issues with these when fitted on road cars (they're popular here on race cars though). I'd consider it, but they're a lot more expensive to replace than a standard water pump for most cars, and when I have seen several reports of them failing within a couple of years of being fitted I would think twice. However, this may be much less of an issue if fitted to a less commonly used classic (maybe more like a race car in hours of use)?
Andrew F

An electric water pump (only) seems like "a bridge too far" to me. A nice idea, but if it failed you wouldn't go many yards before the coolant turned to steam! A faulty electric water pump is not going to respond to the "ladies tights treatment"! I can, however, recommend substituting the mechanical fan with an electric one. If that fails, you are only in trouble if you get stuck in traffic for more than 5 or 10 minutes. The fan is not needed over 30 miles an hour.
Lindsay Sampford

Barry--yes, the system runs independently for a few minutes after shut-down. But all you're doing is recirculating hot water. I don't see that as being able to stop heat soak.
JM Morris

Yes, it reduces the heat soak problem some. Hottest point in the cooling system is where the temperature sensor probe resides, at outlet from the head just below the thermostat. When running, temperature around the exhaust ports is considerably higher than the measured coolant temperature. When you shut the engine off the coolant stops circulating (except for a little thermal siphon action). Heat around the exhaust ports then soaks through the casting wall to warm the fluid, and the indicated temperature rises considerably.

If you have an electric water pump, and it will run for a few minutes after engine shut down, it will circulate the cooler fluid from bottom of radiator throughout the engine. This will effectively prevent the fluid temperature rise in the area of the temperature probe. Even without a fan running, the radiator will continue to dissipate some heat from the fluid, if it will circulate. The electric pump assists thermal siphon for this purpose.

Reducing cylinder head peak temperature rise by 10dF after shutdown might be just enough to keep the carburetors from boiling fuel a few minutes later.

I like the idea of an electric water pump for the same reason as an electric fan. It takes a significant load off the engine at road speed and when you need max power.
Barney Gaylord

Barney .....have you fitted an electric water pump to yours? Whether you have or not what pump would you recommend and where to place? presume you have ( would?) remove the existing impeller . I already have electric fans and they made a noticeable difference re power ( as measured by the hoof ) and will be fitting a Judson in next few months so after efficiencies everywhere in parallel.
Neil Ferguson

I have not, but would like to give it a try some day.

It might be nice if there was an electric pump that fit in place of the original water pump, but probably not much chance there. If you could drive the alternator from crankshaft with a direct belt and no water pump pulley, it may be good to fit a flange and pipe in place of the original water pump, then use the EWP80 Pump electric pump.

Some years ago I saw an MG midget in racing form with a simple electric water pump. The car ran short races, so could charge the battery in the paddock and didn't need a generator. The guy had mounted a heater motor in place of the generator to run the original water pump with a small toothed belt. It worked well and looked like a cheap installation. At the time I was surprised how slow it ran, not much more than tick over speed on the water pump. A 4-amp, 50 watt electric motor can pump quite a lot of water in a large bore circuit without running the pump very fast.
Barney Gaylord

What I don't see is how an electric pump would reduce much if any engine load at road speed. You have to take mechanical power from the engine to run the generator or alternator and convert that into electrical power and then an electric motor converts that back into mechanical power to run a pump. The whole process is probably only 50% efficient at best.

An electric fan can be shut off completely at speed because you have the air flow, but you still need to be circulating water to the radiator so you can't shut down the pump completely. Slowing the flow to just what is needed would help reduce power some, but doubt it would help enough to offset the loss in the mechanical-electrical-mechanical conversion process. With the current emphasis on fuel efficiency you would expect to see electric pumps on new cars if they provided much if any reduction in engine load. While almost all new cars have electric fans, as far as I know most still have mechanical pumps.
Jeff Schultz

Centrifugal pumps are only efficient in a narrow RPM range, but cooling is needed over a very wide range, about a factor of ten, from idle to redline. So, to compensate, the water pump has to be designed with far more capacity than ever needed, mostly to provide adequate cooling at low speeds. Even then it gets dicey, since at high speeds the additional capacity makes cavitation more likely, and the excess capacity is always using more power than is required. The great advantage of an electric pump is that it can be designed for whatever maximum circulating capacity is desired, at a constant pump rpm. This means you get max cooling at idle or when pulling a heavy load at low speed, with no cavitation at high speed. If you then want to reduce losses even more, you can power it through a PWM speed control for some but not max circulation. You could get very sophisticated and vary the pump output by measuring temperature differential across the engine from water in to water out; also temp differential across the rad to vary fan output. The ability to run it after shutdown is pure gravy, but quite useful; running a fan then adds even more anti-boil on hot shutoff.

FR Millmore

The electric pump running at constant speed takes 7.5 amps current draw, which is about 0.13-hp electrical input. If an alternator is 80% efficient converting belt drive to electric, then it needs about 0.16-hp to handle the increased electrical load on the alternator.

Under certain circumstances the electric water pump can be electronically slowed down to draw even less power. The belt driven pump surely takes more mechanical power than that at normal road cruise speed, and far more at high speed when you want max power.

So the electric water pump saves power and improves fuel economy, because it does not pump excessive amounts of water like the belt driven pump does at high speed.
Barney Gaylord

This thread was discussed between 04/01/2012 and 07/01/2012

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