35 replies to this topic

[robroy]

Hello everyone.
I'm thinking about replacing my old mechanical water pump for an electric one, and was wondering if anyone else had used them on their race or road car, and if they were up to the task?

Most designs I've come across are similar to this:
http://www.thinkauto.../waterpumps.htm

My 1300cc engine only requires 100bhp worth of cooling so the smallest ones, up to 80 litres/min, should be more than adequate, however, while the advertising claims are good, some internet folk have claimed that the centrifugal design doesn't flow as much as a mechanical pump at higher speeds, or with back pressure, and has caused overheating problems with their bigger engines. I guess I should be safe with my small engine, but thought it would be wise to ask.

Also, can anyone suggest any different aftermarket designs that are available, and are there any small or medium sized production cars built with electric water pumps?

[McGuire]

Well, theoretically you need around 2.5 liters per minute per kilowatt of engine output, on the outside. (Yon Rule of thumb.) But it can vary over 100 percent either way depending on the engine's state of tune, cooling system efficiency, etc. The danger is at extended high load where nucleate boiling can run away if the flow volume is insufficient, and the flow requirement at high rpm/high output is remarkably high.

Crank-driven water pumps have built-in idiot-proofing: The faster the engine turns, the faster the pump turns in direct proportion.

Electric pumps operate at constant speed independently of engine rpm, which is rather inelegant (unless you are in the mood for cooking up some fancy square wave controller hardware).

So personally, in road car applications I would stay away from electric pumps unless there is some packaging/clearance issue to be solved. If proceeding I would prepare for some sorting; bolting one up and forgetting it is asking for trouble.

One more interesting thing I have seen: with a belt-driven pump, if the impeller catches a piece of gasket, scale, silicone, etc., it will invariably clear the foreign material and the pump will keep on working fine. With an electric pump the impeller stops, the circuit-breaker opens and no more water pumping. When you take the cooked engine apart for rebuilding, you find the little piece of gasket or whatever still lodged in the impeller.

[Bill Sherwood]

http://www.daviescra...play.asp?pid=47

This is what you want, they work rather well in conjunction with the controller. A couple of cars in my 1300cc class use them and if the pump is kept cool they give no trouble.

[OfficeLinebacker]

I've played with electric pumps when I was in the drag racing scene, and with those it was common, even in "streetable" cars, to have to stop and let the pump and the fans run after a short bit of driving. So that's one advantage, you can cool down the engine even when the engine is off.

[McGuire]

Many production cars are wired so that the electric cooling fan runs through one or two temp cycles after the ignition is shut off. At least one, the Lotus Carlton, had an auxiliary electric water pump that circulated coolant when the engine was shut off to fight off heat soak.

A lot of street/strip type cars have used electric water pumps. Good way to identify a for-real street car... if it has an electric water pump it probably isn't. Will sort of work with a mild small-block if the application is not too taxing. A/C or big-blocks, forget it.

[kikiturbo2]

Originally posted by McGuire
At least one, the Lotus Carlton, had an auxiliary electric water pump that circulated coolant when the engine was shut off to fight off heat soak.

lots of VW's, like VR6 engines, also Renault 19 S16 etc. used a small Bosch electric water pump that circulated water after the engine shutdown..

I am thinking of using an electric water pump in my BEC middy, powered by a suzuku GSXR engine, that might need a dry sump, which uses a pump driven off the water pump shaft, hence no more mechanical pump.... but I am really worried about the pump failure..

[McGuire]

To me that is one of the more suitable applications for an electric water pump. Nice small engine, packaging issues.

[J. Edlund]

BMW uses a 200 Watt electric coolant pump on some of their newer engines, but on these engines the pump and the electric thermostat is under control by the EMS. The cooling system is also designed for a low pressure loss.

Originally posted by McGuire
Well, theoretically you need around 2.5 liters per minute per kilowatt of engine output, on the outside. (Yon Rule of thumb.) But it can vary over 100 percent either way depending on the engine's state of tune, cooling system efficiency, etc. The danger is at extended high load where nucleate boiling can run away if the flow volume is insufficient, and the flow requirement at high rpm/high output is remarkably high.

Seems a bit much. The engines I know of have pumps that provide about 1-1.5 liters per minute and kW of engine output.

[NRoshier]

All of the DC EWP's I have seen recently have been controlled via the EMS, which switches the pump on/off and to what speed dependant on engine coolant temp. Pump runs for some time after shutoff.

[Paul Vanderheijden]

I can offer some direct personal experience. I have been using the EWP80 pump as the primary, and only pump, on my 1 litre Abarth motors that put out over 100 HP. Water temperature ranges from 180F at the low to 215F at the high. I ran the EWP80 for the first time in 2001 and was the first competitor in the Abarth Coppa Mille to use it. Today, EVERY serious competitor in this series runs either the EWP80 or EWP100 pump.

Some competitors choose to use the pump without a controller and simply run it at full speed, regulating water circulation with a "restrictor sleeve". Personally, I have always used the EWP80 pump with an analogue controller. With this device the pump becomes a variable voltage, variable speed pump, and only runs fast enough to keep the water temperture around the temperature set on the controller.

No electric water pump is a panacea for a poorly performing radiator system. If the radiator is efficient, then the EWP pumps will work OK.

On my own engines I have mounted the pump on a special adapter, directly on the block, with a phenolic spacer between the pump and the adapter. This seems to work well.

Since 2001, I have only heard of a single structural failure of one of these pumps, where the housing actually fractured. This car had been involved in a multiple rollover and rebuilt, so it is hard to say for what reason the structural failure actually occurred.

Regards,
Paul Vanderheijden

[phantom II]

What modern car has an engine driven fuel pump?

[kikiturbo2]

there is one thing that is bugging me with regards to the variable speed controlers and electric pumps...
I always thought that water pressure is needed in the head to prevent localised boiling...? so switching the pump off during running might be dangerous even though radiator temp is ok..?

[kikiturbo2]

Originally posted by phantom II
What modern car has an engine driven fuel pump?

AFAIK all the direct injection engines have a engine driven mechanical pump (high pressure one..) with a high volume low pressure electric pump in the tank...

[cheapracer]

Originally posted by kikiturbo2
there is one thing that is bugging me with regards to the variable speed controlers and electric pumps...
I always thought that water pressure is needed in the head to prevent localised boiling...? so switching the pump off during running might be dangerous even though radiator temp is ok..?

It's not the pump that provides the pressure, it's the heat expanding the water.

[kikiturbo2]

I am aware of that, but the pump does provide more pressure in the head as the thermostat provides a restriction to the flow... but seeing that people are ok with most of the electric pump instalations I guess it is a non issue..

[mariner]

Does anybody have any "rules of thumb" for radiator size versus KW/bhp of power output. I can surmise that it varies according to location ( front/side) ducting etc but is there any sort of, say two or three dimensional rule of thumb. Say X sq cm/in per KW at Y airflow through the rad. core at Z water flow rate?

Which begs the question is there an optimum water flow rate ( as I would think this is the first question when deciding the pump size)?

[ferrarifan2000]

what about an electric turbo?

[Greg Locock]

Electric superchargers are available, as are turbo electric generators (at least experimentally at an automotive scale). Which are you interested in?

[ferrarifan2000]

I was just wondering if electric powered turbo existed to keep the engine 'on boost' during lower rpms. Thanks for the reply.

[kikiturbo2]

Originally posted by ferrarifan2000
I was just wondering if electric powered turbo existed to keep the engine 'on boost' during lower rpms. Thanks for the reply.

Garret did some work in electrically assisted turbochargers, to help lower spool time... However, IMHO modern engines with twin scroll turbos suffer verry little lag, not to mention variable geometry turbochargers which are even better.. so electrically assisted turbos might be an overly complex solution for a non existing problem..

[Paul Vanderheijden]

First, somehow we have gotton fuel pump and water pump issues intertwined. This message is regarding waterpump issues.

The EWP brand of electric water pumps and controllers work on the basis that as the cooling liquid increases in temperature, the speed of the pump increases. Your assumption was that the pump would stop turning at some point in time. This is incorrect. While at room temperature the pump does turn very slowly, nevertheless it never stops completely.

As it increases speed and hence pressure, with an increase in water temperature, it inherently can deal with minimizing the formation of steam pockets, which only occur once the liquid medium approaches boiling point. There may be "air pockets", and these would be treated identically by either a mechanical or electric water pump.

With regards to water pump flow, consider the following. One of the age old stories is that if you remove the thermostat, the water will "rush" through the radiator and not have time to shed its heat. This assumption is flawed. If we assume that the radiator has a finite heat dissipation capacity or temperature delta, and with thermostat in place the water makes one circuit per minute, then there will be "X" time for the radiator element to absorb heat from the fluid. If we now remove the thermostat, causing the flow rate to double, then the argument would be that the cooling liquid only spends half the time in contact with the radiator element. Yes that is true, but in the same total time period of one minute the same fluid would make two passes through the radiator element. As such, the total heat transfer would be the same. Heat is therefore added and released from the cooling fluid incrementally on each circuit.

As the engine heats up, there will be a continuum of "points of equilibrium" based on total heat produced and total heat shed. Vehicle speed and the CFM of air through the radiator help in balancing the situation. At idle the radiator may be capable of dealing with all of the heat produced, and as the speed of the vehicle increases increasing amounts of head load can be dissipated.

As regards coolant pressure, the effect of a thermostat, or restriction orifice, is to cause the water to be "********" somewhat. This inherently causes a small pressure increase in the block. As centrifugal pumps are not good at creating pressure, the effect is limited. It does however account for a small increase in the boiling point of the fluid trapped behind the thermostat or restrictor plate.

In my own experience, the ability of a variable voltage, and hence variable flow, water pump aids in keeping a relatively constant water temperature range. In many modern race cars the oil is cooled using an oil-to-water intercooler. This will add some additional heat loading to the system, but greatly assists in packaging.

Paul

[robroy]

Thanks everyone. Interesting stuff as ever.

It looks like I'll definitely be needing a controller if/when I do go for an electric pump then.
My old Fulvia water pump does have to pump to a radiator that's 2 metres farther away than it should be, but has coped admirably for 2 years, until last weekend. I've found another one in the meantime, so I need not rush in.

I was hoping most modern cars might have switched to EWP's by now. As suggested earlier, most petrol cars switched to electric fuel pumps long ago.

I hadn't thought of combining oil and coolant cooling duties with one pump. I shall spend some time thinking about this. Out of interest, is there much difference in power loss between a mechanical pump via a pulley/shaft and an electric one via the alternator?

I quite like the idea of an electric supercharger, maybe in conjunction with regenerative brakes.

[J. Edlund]

Originally posted by kikiturbo2


Garret did some work in electrically assisted turbochargers, to help lower spool time... However, IMHO modern engines with twin scroll turbos suffer verry little lag, not to mention variable geometry turbochargers which are even better.. so electrically assisted turbos might be an overly complex solution for a non existing problem..

One of the problems with these assisted turbochargers is that they need something more powerful than the ordinary 12V system to have a significant effect, and if you have, say a 42V system you can simply put the power directly to the crankshft through a starter/alternator instead.

The easiest way to provide a fast response and extended power range is probably two stage charging. The end result is better than variable geometry turbos without those heat sensitive variable vanes.

[kikiturbo2]

of course.. 42V is the key... although, having driven the last generation of turbo cars (and owning a Evolution 9 with twin scroll turbo and variable timing in the cams) I can honestly say that turbo lag in modern cars doesn't bother me..

PSA/BMW 1.6 litre petrols with variable geometry turbos are just superb, very little lag, even my mitsubishi that has a huge twin scroll turbo (capable of dishing out 420 HP on a two litre engine) is an easy drive.. but I credit that to the variable cams..

so I think that electrically assisted turbos might be an overly complicated solution to the problem that has been solved with other means..

similar thing is with electgric water pumps on road cars.. it is a potential failure point compared with mechanical pumps that work flawlessly.. and if you take into the account that BMW is using a technology to shut down the pump when it is not nedeed, then you also are able to get added eficciency with a mechanical system..

[britishtrident]

A couple of points that may be of interest

Cavitation ---- impeller pumps don't work well at high RPM, a phenomena called cavitaion cases the formation of tiny bubbles of superheated steam on the surface of water pump rotor's vanes if it is turning above its design RPM, this knocks the pumping efficiency out the window. For a high rpm racing engine based on a production unit a belt driven water pump speed needs to be geared down to about 1/2 the speed of the road cars for best coolant flow and reduced pumping losses.

Thermostats --- all engines should have thermostats and very importantly by-pass hose connection. The By-pass connection which is a small bore hose running from the top of the cylinder head (before the thermostat) to the water pump inlet ensures a more even distribution of temperature through the engine. The by-pass hose is essential if you fit a thermostat as without a by-pass hose the thermostat won't open until the engine is near boiling.


Just before they closed MG-Rover Power Train developed an interesting range of remote thermostats for the 4 cylinder K series to prevent head gasket problems. These "PRT" (somtimes called PRTT) remote thermostats open under both temperature and flow pressure for more details see this site
http://web.tiscali.it/elise_s1/

[scooperman]

I thought BMW had a tidy pump design on the K-series bike engines, the oil and water pump are one common casting, the water impeller and oil pump gears are on two sides of a common-shaft pump assembly.

Disagree with some of Paul's claims about thermostat removal. I suppose it could be true in an engine with a very good water flow path. But in many engines, if the thermostat is near the pump at the front of the block, then when it is removed, much water will circulate from the pump right back to the radiator...not as much will flow around the rear cylinders and up through the deck to the back of the head as it did when the thermostat was installed. So the back cylinders run hotter. Usually one replaces the thermostat with a blanking sleeve, or a gutted thermostat, which still provides some restriction to flow.

[OfficeLinebacker]

Originally posted by phantom II
What modern car has an engine driven fuel pump?

[britishtrident]

Originally posted by Paul Vanderheijden

snip

With regards to water pump flow, consider the following. One of the age old stories is that if you remove the thermostat, the water will "rush" through the radiator and not have time to shed its heat. This assumption is flawed. If we assume that the radiator has a finite heat dissipation capacity or temperature delta, and with thermostat in place the water makes one circuit per minute, then there will be "X" time for the radiator element to absorb heat from the fluid. If we now remove the thermostat, causing the flow rate to double, then the argument would be that the cooling liquid only spends half the time in contact with the radiator element. Yes that is true, but in the same total time period of one minute the same fluid would make two passes through the radiator element. As such, the total heat transfer would be the same. Heat is therefore added and released from the cooling fluid incrementally on each circuit.

snip
Paul

What has to be understood is the designer aims for an even spread of temperature throughout the cylinder block, to get this you need a thermostat and proper bypass circulation. Essentially job of the bypass is that the coolant must be kept circulating within all parts of the block even when the thermostat is closed to prevent hot and cold spots forming within the water jacket.

scooperman is correct if the thermostat is removed on production cars a restrictor plate to replace the thermostat is usually required to ensure proper circulation round all the cylinder bores. BMC Special Tuning had a part number for such part for the Mini Cooper S also MG-Rover fitted one when they relocated the thermostat on the K series 4 cylinder.

Also apart from obvious reasons such as keeping crankcase temperature high enough to avoid condensation of water and acid products of combustion in the sump keeping the cylinder water jacket properly warm reduces the heat loss to the coolings system ie it increases the specific BMEP.

The challenge is in keeping the cylinder head cool enough and the water jacket warm enough without local over heating or over cooling.

[slucas]

no,no .He said modern.

[zac510]

Fuel pump and water pump are different requirements as far as I see it, so incomparable. For example an engine driven fuel pump would be a disadvantage because it won't build fuel pressure until it's cranking or running. A cooling system isn't as critical in that phase.

[Paul Vanderheijden]

Hello BritishTrident and Scooperman,

Perhaps my comment was somewhat confusing. I am not at all advocating the total removal of a thermostat or restrictor plate. Quite the contrary. In conjunction with an electronically controlled electric waterpump you get the best of both worlds.

My comments were directed at competition type motors. Here a restrictor plate is in my view the best alternative and allows continual circulation of cooling fluid, whether with a bypass or not.

One other area where the electronically controlled water pump really shines is in the area of pump cavitation prevention. Many times I see water pumps that are overdriven. In one case, where I was shipped an engine by a competitor, the pulley on the waterpump was half the diameter of that on the crankshaft. So at 6000 engine RPM the pump was turning 12000 revolutions. At this speed not only does the pump tend to introduce air into the coolant, it is highly likely that there is a significant pressure drop at the entry to the pump, causing boiling of the fluid. Of course once this happen, then not water is circulated at all. The engine failed due to a SEVERELY blown head gasket. In fact the failure of the head gasket prevented the total detonation of 3 pistons.

It has been my experience that anything over 4000 waterpump RPM is counter productive.

Paul

[Bill Sherwood]

Originally posted by Paul Vanderheijden
Many times I see water pumps that are overdriven. In one case, where I was shipped an engine by a competitor, the pulley on the waterpump was half the diameter of that on the crankshaft. So at 6000 engine RPM the pump was turning 12000 revolutions. At this speed not only does the pump tend to introduce air into the coolant, it is highly likely that there is a significant pressure drop at the entry to the pump, causing boiling of the fluid. Of course once this happen, then not water is circulated at all. The engine failed due to a SEVERELY blown head gasket. In fact the failure of the head gasket prevented the total detonation of 3 pistons.

It has been my experience that anything over 4000 waterpump RPM is counter productive.

Paul

I quite agree - the last 4AGE I built I ended up running the water pump at about half the factory speed and it worked rather well. The only problem was when running the engine in I had to keep the stock water pump pulley to keep the speed up as the engine was pretty tight and got a little warm for my liking. Once it had about 2,000km on it and was well on the way to being fully run-in I swapped back to the big pump pulley and it took longer to warm up.

[britishtrident]

Link to good picture of a PRT thermostat

http://www.lrseries....-THEMOSTAT.html

[Ben Wilson]

Originally posted by robroy
My old Fulvia water pump does have to pump to a radiator that's 2 metres farther away than it should be, but has coped admirably for 2 years, until last weekend. I've found another one in the meantime, so I need not rush in.

I've got a Davies Craig which worked very nicely in my mr2 (front radiator/mid engine). The only problem is that I was running it without a thermostat or restrictor so I had no heater...

[robroy]

Originally posted by Ben Wilson


I've got a Davies Craig which worked very nicely in my mr2 (front radiator/mid engine). The only problem is that I was running it without a thermostat or restrictor so I had no heater...

Must get chilly! How do you demist the windscreen? I hear BMW do a nice electric demister for their convertibles.
Have you done a lot of mileage on the water pump?

[Ben Wilson]

Originally posted by robroy


Must get chilly! How do you demist the windscreen?
Have you done a lot of mileage on the water pump?

I only drove it on nice days ;)

I pulled it off the road (for other reasons), before too long (probably 5000km) or so.. One day this decade I hope to get it back on the road again...