Electric Water Pumps (EWP)
Posted: Thu May 19, 2016 2:11 pm
I figured I'd start a thread on EWP's so that everyone can contribute to it. There are quite a few threads out there touching on them but I'll try and summarize coolant theory, pros / cons of EWP and installation.
The idea behind running an EWP is mostly two fold. It frees up horse power and it can give more effective cooling at idle or when the engine is shut off. For these reasons, I think you'd only look to install one if you're competing in motorsport. So the general gist is to remove the insides or blank off the water pump and then mount a EWP somewhere in the coolant path to circulate the coolant. They are either controlled via an external controller or via an ECU that uses a coolant sensor to control the speed of the water pump.
There are a couple of key benefits
1. More consistent coolant flow through the head
So the idea here is that you can keep a fast flow of coolant regardless of the RPMs of the engine. This keeps the head temp even across it's length. A mechanical pump will push more coolant through the engine at high revs, however there can be so much flow that the coolant at the pump can cavitate and cause air bubbles. At idle the stock water pump slows down a lot and is circulating far slower than an EWP can. With an EWP, if the coolant temp is high, the water pump will cycle the coolant at it's fastest rate until that coolant temp drops below the required threshold regardless of if the engine is being dríven or sitting in the pits idling. With an EWP coolant speed is only linked to coolant temp.
There is also the option with EWP to reverse the flow of coolant. So instead of entering the block at the mechanical water pump, flowing through the block, up into the head and then out the front or back (dependent on Coolant re-route) to the radiator, the coolant runs through the head first, potentially entering at both the front and the back of the head. If you reverse the flow of coolant through the engine, it would be advisable to do this so that any air trapped up in the head can be extracted through and out the block. The benefit here is that the head is getting the cool water directly from the radiator before it's heated by the block reducing reducing temperatures significantly across the whole head.
2. EWP frees up HP
This is really only true at high revs. The mechanical pump saps a lot of power at 8000 rpm as it's being dríven at a faster rate than it was designed. The power it uses goes up exponentially with revs until the coolant starts to cavitate. The amount of power the water pump uses is debatable, but I think it's probably in the range of 2-10HP. The EWP water pump can use up to 8 amps of power to drive, which is basically taken from the engine via the alternator or battery if the engine isn't running. That means approx 0.3HP of power taken from the engine via the alternator (assuming 50% efficency). So all up there is some gain to not running an mechanical pump... especially if you are reving the engine a lot.
3. No thermostat
In order to run a EWP you need to remove the thermostat. Instead of the thermostat here are a few different methods to get heat into the engine quicker. One of those is using a solid state relay on a PWM to rapidly pulse the EWP making it turn slowly. Alternatively you can pulse the EWP in 5 second brackets until the coolant reaches a threshold and the EWP turns on full time. This is basically what the Davies Craig controller does. Electronic set up and control will depend a lot on what ECU you are running.
There is claimed benefit of the thermostat in that it creates a restriction that causes a build up of pressure in the head. The theory is that this leads to less localized boiling or hot spotting. Personally I'm not sure on this claim given that when the thermostat is present the coolant is flowing slower in the first place. I think the speed of coolant flow through the head helps drive down the temp delta across the head which would give a greater benefit than the 2-3 PSI of increased pressure due to the restriction caused by the thermostat. In my track car I don't run a thermostat for this reason.
4. Failure rate
Switching from a mechanical belt dríven water pump + thermostat to an electrical water pump as pros and cons. I'm not sure which is more risky but given that stock water pumps don't fail that often I think the EWP probably has a higher likelyhood of failure. The EWP itself has apparently a very low failure rate, so I see more risk in the electrics failing. The good thing about electrics is that they can be set up to display a warning light if failure occurs, subject to the correct setup, whilst a mechanical water pump gives no warning.
Overall, we don't see many installations of EWPs on MX5s. As a result we don't have a lot of information on how effective running the coolant in reverse actually is and if there are any issues like trapped air bubbles etc. EWPs are used commonly on racecars as the benefits of the extra HP and overall better cooling control, especially in the pits is seen as worthwhile. Over the next few months as I install mine, I'll document what I find.
The idea behind running an EWP is mostly two fold. It frees up horse power and it can give more effective cooling at idle or when the engine is shut off. For these reasons, I think you'd only look to install one if you're competing in motorsport. So the general gist is to remove the insides or blank off the water pump and then mount a EWP somewhere in the coolant path to circulate the coolant. They are either controlled via an external controller or via an ECU that uses a coolant sensor to control the speed of the water pump.
There are a couple of key benefits
1. More consistent coolant flow through the head
So the idea here is that you can keep a fast flow of coolant regardless of the RPMs of the engine. This keeps the head temp even across it's length. A mechanical pump will push more coolant through the engine at high revs, however there can be so much flow that the coolant at the pump can cavitate and cause air bubbles. At idle the stock water pump slows down a lot and is circulating far slower than an EWP can. With an EWP, if the coolant temp is high, the water pump will cycle the coolant at it's fastest rate until that coolant temp drops below the required threshold regardless of if the engine is being dríven or sitting in the pits idling. With an EWP coolant speed is only linked to coolant temp.
There is also the option with EWP to reverse the flow of coolant. So instead of entering the block at the mechanical water pump, flowing through the block, up into the head and then out the front or back (dependent on Coolant re-route) to the radiator, the coolant runs through the head first, potentially entering at both the front and the back of the head. If you reverse the flow of coolant through the engine, it would be advisable to do this so that any air trapped up in the head can be extracted through and out the block. The benefit here is that the head is getting the cool water directly from the radiator before it's heated by the block reducing reducing temperatures significantly across the whole head.
2. EWP frees up HP
This is really only true at high revs. The mechanical pump saps a lot of power at 8000 rpm as it's being dríven at a faster rate than it was designed. The power it uses goes up exponentially with revs until the coolant starts to cavitate. The amount of power the water pump uses is debatable, but I think it's probably in the range of 2-10HP. The EWP water pump can use up to 8 amps of power to drive, which is basically taken from the engine via the alternator or battery if the engine isn't running. That means approx 0.3HP of power taken from the engine via the alternator (assuming 50% efficency). So all up there is some gain to not running an mechanical pump... especially if you are reving the engine a lot.
3. No thermostat
In order to run a EWP you need to remove the thermostat. Instead of the thermostat here are a few different methods to get heat into the engine quicker. One of those is using a solid state relay on a PWM to rapidly pulse the EWP making it turn slowly. Alternatively you can pulse the EWP in 5 second brackets until the coolant reaches a threshold and the EWP turns on full time. This is basically what the Davies Craig controller does. Electronic set up and control will depend a lot on what ECU you are running.
There is claimed benefit of the thermostat in that it creates a restriction that causes a build up of pressure in the head. The theory is that this leads to less localized boiling or hot spotting. Personally I'm not sure on this claim given that when the thermostat is present the coolant is flowing slower in the first place. I think the speed of coolant flow through the head helps drive down the temp delta across the head which would give a greater benefit than the 2-3 PSI of increased pressure due to the restriction caused by the thermostat. In my track car I don't run a thermostat for this reason.
4. Failure rate
Switching from a mechanical belt dríven water pump + thermostat to an electrical water pump as pros and cons. I'm not sure which is more risky but given that stock water pumps don't fail that often I think the EWP probably has a higher likelyhood of failure. The EWP itself has apparently a very low failure rate, so I see more risk in the electrics failing. The good thing about electrics is that they can be set up to display a warning light if failure occurs, subject to the correct setup, whilst a mechanical water pump gives no warning.
Overall, we don't see many installations of EWPs on MX5s. As a result we don't have a lot of information on how effective running the coolant in reverse actually is and if there are any issues like trapped air bubbles etc. EWPs are used commonly on racecars as the benefits of the extra HP and overall better cooling control, especially in the pits is seen as worthwhile. Over the next few months as I install mine, I'll document what I find.
I'm just gonna hang back and watch where this goes.
