Cooling System Build Thread

Jonohhh

Jonohhh

True Classic
Hi all.

So, despite the list of things to do to my X1/9 being quite long, one has taken precedence over the last couple of months. I must admit, most of my motivation comes from not wanting to do a head gasket replacement due to an overheat. My old and Italian cooling system is barely holding on, which does not bode well given my driving style.

Because the water pump is quite annoying to access on my 85' 1500 with Air Conditioning, and hardly adequate under all conditions in stock form, I have decided to do away with its function and never look at it again.

This thread will detail the final design, implementation, considerations made, and lessons learned during the process.

And so it begins:

Key Points:

  • The radiator fans will be controlled variably based on radiator outlet temperature instead of radiator inlet temperature.
  • The mechanical water pump will be replaced by an electric water pump, and controlled variably based on engine outlet temperature.
  • The bypass style thermostat will be retained, and the pump placed such as to function identically to the OEM pump, in order to retain proper heater function, and to keep engine temperature deltas at acceptable values. This latter point is especially important and often overlooked.
  • Each control system, three in this case (rad fans, thermostat, water pump output), will be optimized to result in a reasonable compromise between cooling system performance characteristics and energy consumption, as to minimize unnecessary strain on the similarly...challenged...electrical system.

I will try to stay relatively light on the philosophy behind each design decision unless requested, as given my tendency to not be able to use few words, the posts would be 4 miles long. (This didn't work well, and resulted in more questions than answers for many, so I apologize in advance about the extremely long posts.)

Rest assured, each decision made has had a lot of thought put into it and is being done for a reason I consider to be thoroughly valid. If anyone has questions or concerns about any of the design decisions I've made, I will be glad to explain, in detail, why I've done what I've done. Like always, I am open and accepting of criticism and differing views, provided there is an explanation of why something else may be more ideal. This project is not for everyone, that should be abundantly clear, but truthfully it's not that complex in the end. The huge majority of the text below comes from feeling the need to explain everything as clearly as possible.

In a couple of weeks I'm out of school for the summer, and will be able to get this done over the following few months. I wanted to go ahead and create the thread so that I can document the parts used, and the configuration of the system. I'll be adding to this thread slowly but consistently until then. It will be broken up into sections: Design, Implementation, Results.
 
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Jonohhh said:
Hi all.

So, despite the list of things to do to my X1/9 being quite long, one has taken precedence over the last couple of months. I must admit, most of my motivation comes from not wanting to do a head gasket replacement due to an overheat. My old and Italian cooling system is barely holding on, which does not bode well given my driving style.

Because the water pump is quite annoying to access on my 85' 1500 with Air Conditioning, and hardly adequate under all conditions in stock form, I have decided to do away with its function and never look at it again.

This thread will detail the final design, implementation, considerations made, and lessons learned during the process.

And so it begins:

Key Points:

  • The radiator fans will be controlled variably based on radiator outlet temperature instead of radiator inlet temperature.
  • The mechanical water pump will be replaced by an electric water pump, and controlled variably based on engine outlet temperature.
  • The bypass style thermostat will be retained, and the pump placed such as to function identically to the OEM pump, in order to retain proper heater function, and to keep engine temperature deltas at acceptable values. This latter point is especially important and often overlooked.
  • Each control system, three in this case (rad fans, thermostat, water pump output), will be optimized to result in a reasonable compromise between cooling system performance characteristics and energy consumption, as to minimize unnecessary strain on the similarly...challenged...electrical system.

I will try to stay relatively light on the philosophy behind each design decision unless requested, as given my tendency to not be able to use few words, the posts would be 4 miles long. Rest assured, each decision made has had a lot of thought put into it and is being done for a reason I consider to be thoroughly valid. If anyone has questions or concerns about any of the design decisions I've made, I will be glad to explain, in detail, why I've done what I've done. Like always, I am open and accepting of criticism and differing views, provided there is an explanation of why something else may be more ideal.

In a couple of weeks I'm out of school for the summer, and will be able to get this done over the following few months. I wanted to go ahead and create the thread so that I can document the parts used, and the configuration of the system. I'll be adding to this thread slowly but consistently until then.
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It all sounds good.
A couple of things.

  • The radiator fans are controlled based on the lower section of the radiator near the outlet not coolant intake temp into the radiator, I would use the same location for the sensor so you don’t get behind the curve so to speak.
  • I do like the idea of knowing the radiator outlet temp but wouldn’t want it to be point one controls the fans from, you don’t want to have to fully cool the mass of the radiator in addition to the incoming coolant.
  • I would suggest keeping the cooling fan approach simpler by using the VW two temp fan switch. It is stupid simple and effective.
I like the concept, it parallels what I have also been thinking. I look forward to seeing what and how you do it.
 
kmead said:
It all sounds good.
A couple of things.

  • The radiator fans are controlled based on the lower section of the radiator near the outlet not coolant intake temp into the radiator, I would use the same location for the sensor so you don’t get behind the curve so to speak.
  • I do like the idea of knowing the radiator outlet temp but wouldn’t want it to be point one controls the fans from, you don’t want to have to fully cool the mass of the radiator in addition to the incoming coolant.
  • I would suggest keeping the cooling fan approach simpler by using the VW two temp fan switch. It is stupid simple and effective.
I like the concept, it parallels what I have also been thinking. I look forward to seeing what and how you do it.
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Hey!


Thanks for the feedback. Some of the decisions (mainly fans being controlled via rad outlet temperature) will make much more sense once I'm able to detail that a bit better. I may end up going a little deeper into the design decisions, just to make things as intuitive as possible.

The two stage fans setup will indeed be using a VW 2 stage fan switch- which I learned about thanks to you and Dr.Jeff. Should work quite nicely for how simple of a solution it is.
 
I believe there is a Porsche version of the two stage switch which has a lower start temperature. I don’t have its part number but one does run across it in a search.

I don’t doubt that there is much thought (and sense) in your design concept :) Occasionally there is some of that in my work.
 
Where do people get the idea that the stock water pump / cooling system is less than adequate for the job?

I regularly build these engine to excess of 100 RWHP / 135 plus Hp at the crankshaft, so pretty close to double the output of the standard engine, and never have I had to use anything other than the stock parts to keep them cool.

At close to double the horsepower of stock at the back wheels the cooling system is dissipating probably twice the calorific value in heat that finds it's way into the cooling system... and the standard parts in good condition have absolutely no problem doing this.

If you need a second fan to keep things cool, you've got something else amiss with the system.

I'm pretty sure the Lancia montecarlo uses the same radiator as the X19, it uses a much larger engine that makes more power, and again more power production = approx 1/3 of that finds it's way into the cooling system as heat loses from the combustion process.

SteveC
 
I think a lot of the reputation our cars have for "overheating" is in reality a demonstration of how misled we have all become by modern vehicle construction and practice.

Modern cars have a "gauge" of some sort that goes from Position A to Position B and then stays there until something catastrophic happens. What you see on the temp gauge of a modern car is NOT the direct readout of an analog sensor, it's what the programmers were told to show you. I think most people (and the younger one is, the higher the expectation) expect this needle stability from our cars, and it ain't gonna happen.

The cooling systems on our cars can be compared in some ways to an early turbo setup. Those early turbo setups had a lot of turbo lag due to the engine control systems and the overall design not being sophisticated enough to compensate for the wide swings in manifold pressure brought on by unusually long lengths of intake piping, going hither and yon around the engine compartment from the intake point thru the turbo to the intercooler to the throttle body. Nothing can be done to correct this situation, it's just the nature of the beast and its times. Even today's turbo cars have some degree of turbo lag. It just IS.

Our cars also have that lag and for the same reasons, but we could call it "cooling lag." We have that same long path. Rather than some fake news readout supplied by a computer, we have a direct-reading analog sensor sending God's own TRUTH to the temperature needle, and it's gonna make a swing, especially when driving conditions change. 190 is the baseline BUT higher than that is OK under certain conditions. Two or three or four extra hash marks when you're stuck in traffic on a hot day is NOT OVERHEATING.
 
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I view "overheating" on an X (or spider) in two modes. Is it overheating at highway speeds or overheating in slow traffic. High speed overheating is usually caused by an old ineffective radiator, swapping radiators always fixed that problem for me. Low speed overheating could be thermostat, water pump, etc. If you are moving at a decent speed, say 30mph or above, is the function of the fan not needed as you have good airflow through the radiator?

Some guys love to mess with modifications and I have no problem with that, this is a hobby and anything that keeps you amused is good.
 
Part One: Design

I said I was going to stay light on the technical babble, but I retract that statement as it'll probably end up with y'all having more questions than anything, and me probably having to explain things anyway.

Before I begin, I want to mention something:

My goal with this project is not to overcool the engine. In fact, my target temperature is likely going to be around 88C (190f), much like stock. This will help oil get to operating temperature quickly, and ensure it is able to maintain 100c at a minimum. The goal is to create a versatile and consistent system that keeps the coolant temperature across the engine within reason, and the coolant temperature itself less prone to influence from driving and environmental conditions. I never want to have to even think about what coolant temp may be as a result of the current conditions (track day, sitting in traffic, whatever it may be)

There are three distinct control systems in this future cooling system. The goal is for each of these to compliment each other. Some of the design decisions (mainly fan control) may seem counterintuitive at first thought, until you consider all of the "knobs" that can be turned in regards to cooling performance, thanks to the use of an electric water pump.

The water pump: Physical

As mentioned before, the factory water pump will be no more. (The pump will be replaced by a gutted one- however that ends up happening. If bearing and seal replacement is simple I will go ahead and do that. If it is not, I will buy a new pump and gut it before installation. I haven't determined that yet, but that's for the future, not the design aspect.)

This leaves the factory pump serving as nothing but a belt idler and a coolant inlet housing. In its place, a Davies Craig EWP115 will be installed in series with the OEM water pump feed pipe. This leaves every coolant flow route unaltered from the original design, unlike other solutions with the pump placed elsewhere. This is important, because I am retaining the factory bypass style thermostat as it is hugely important to maintaining an appropriately small temperature difference between the engine coolant inlet and outlet. I will refer to this parameter as "engine temp delta" from now on, to keep things simple.

Technical side note: While there are actually performance advantages to being able to have the block at a different temperature than the head, that will be ignored because thats simply beyond the scope of my goals for this system. This means, for my purposes, the lower the temp delta, the better. When this value becomes too high, you run the risk of blowing a head gasket, and causing undue stresses and wear on the engine due to thermal shock and uneven expansion of the block and head. This is important and most always ignored outside of the original designers of the engines cooling system. Even Davies Craig themselves have some truly atrocious system layouts on their website that take this number and throw it out the window.

Water Pump: Control

The water pump will be controlled variably based on the coolant temperature at the engine outlet (note, NOT the radiator feed pipe, the temperature leaving the engine itself, at the hot side of the thermostat housing). This means that the pump can nearly instantaneously respond to changes in cooling system demand. As soon as the coolant that was inside the engine whenever the engine demand changed makes it to the temperature sensor (mere seconds), the pump will immediately speed up in an attempt to get the temperature back down.

For now, assume engine coolant inlet temperature to be constant. More on this later.

This is very easy to validate by looking at the simple equation:

Heat Flow Rate = (Specific Heat of Fluid) * (Mass Flow Rate) * ( Temperature_outlet - Temperature_inlet)

Since we are obviously not changing the specific heat of water on demand, and we will be trying to maintain a constant inlet temperature (controlled by a different control system entirely), the three variables we have are the outlet temperature (where the sensor is), the mass flow rate of the coolant as dictated by the pump, and the rate of Heat Flow.

As soon as engine heat load is increased for the current mass flow rate, the temperature at the outlet will rise. The control system will then increase the speed of the coolant pump, which will bring the outlet temperature down almost immediately.

Since the inlet temperature will be constant, and the outlet temperature targeted to ~8c higher (a generally accepted engine temperature delta), the temperature across the engine should remain consistent as consistent as possible at all times, within the capacity of the radiator.


The Thermostat:

Bypass Thermostats like our stock ones offer some great advantages. Because the engine inlet temp is not coupled to radiator outlet temperature, it's possible to maintain a reasonable temperature across the engine under any driving condition, provided there is adequate coolant flow rate, which is a place that the stock cooling system is lacking.

The thermostat temperature will be such that the bypass is almost all the way closed at target coolant temperature. This allows us to maintain a high coolant flow rate, without overcooling the engine or feeding it excessively cold coolant during low load operation.

This means I am using its control ability entirety to prevent over cooling, and not at all to increase radiator flow rate whenever temperature rises above target- its control range will be nearly maxed out at operating temperature.

If the thermostat temp is too low based on the water pump target, it will stay open and with a shut bypass even when the coolant temperature is below desired value. This negates its advantage during most of the operating time.

If the thermostat temperature is too high compared to target, excessive energy will be wasted by the cooling system as the pump works very hard just to circulate its own water.

Thermostats are proportional devices. They begin to open at a certain temperature and will be fully open by a different temperature, a few degrees higher. I will need to do some testing before deciding on a temperature if I want it to be both efficient and ideal for the engine. I suspect the 82c thermostat may be very close to ideal, but I cannot say for certain yet.


The next part will detail the fan control, which is a crucial part of the way this system is controlled.
 
fiatfactory said:
Where do people get the idea that the stock water pump / cooling system is less than adequate for the job?

I regularly build these engine to excess of 100 RWHP / 135 plus Hp at the crankshaft, so pretty close to double the output of the standard engine, and never have I had to use anything other than the stock parts to keep them cool.

At close to double the horsepower of stock at the back wheels the cooling system is dissipating probably twice the calorific value in heat that finds it's way into the cooling system... and the standard parts in good condition have absolutely no problem doing this.

If you need a second fan to keep things cool, you've got something else amiss with the system.

I'm pretty sure the Lancia montecarlo uses the same radiator as the X19, it uses a much larger engine that makes more power, and again more power production = approx 1/3 of that finds it's way into the cooling system as heat loses from the combustion process.

SteveC
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My cooling system is adequate under heavy driving, whenever the pump is flowing a sufficient volume of water. I regularly go on backroads drives where it spends most of its time at wide open throttle above 5000 rpm, and while it gets a bit warm, its well within reason. I don't doubt that a perfectly functioning stock system can handle quite a bit more power.

The inadequacy in my car comes from daily driving, where what the engine *can* do doesn't matter nearly as much. Sitting in traffic on a warm day, with the engine idling, the coolant temperature rises steadily, even with both radiator fans on. The radiator Outlet temperature gets quite cool, but the engine continues to get hot, which is indicative of insufficient coolant flow rate. The drop off in pump performance is not due to a clogged radiator, as heater performance degrades similarly. Once I get the air conditioning going this is sure to be worse. On top of this, the performance of the heater degrades significantly at idle, and I'd rather it not. The pump is not performing as a factory one should, and the factory one is supposedly just barely adequate for stop and go traffic with air conditioning on, so I'm getting rid of the sub-optimal solution, and going overboard. Keep in mind I am from a place with summers above 100f, with absolutely brutal sun.


While I absolutely love old cars, there are a few areas I believe modernization is never bad. Having to pay attention to coolant temperature is one part of the experience that I am okay with leaving behind.

Cheers,
Jon
 
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Dan Sarandrea (Phila) said:
I think a lot of the reputation our cars have for "overheating" is in reality a demonstration of how misled we have all become by modern vehicle construction and practice.

Modern cars have a "gauge" of some sort that goes from Position A to Position B and then stays there until something catastrophic happens. What you see on the temp gauge of a modern car is NOT the direct readout of an analog sensor, it's what the programmers were told to show you. I think most people (and the younger one is, the higher the expectation) expect this needle stability from our cars, and it ain't gonna happen.
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The point on needle damping is a good one, but no fear, I am very aware of it and am not comparing the gauge behavior of my X1/9 to, say, my E36M3 where the needle stays in one position from 75-115c.

While I acknowledge that there will always be some fluctuation to engine coolant temperature based on conditions, with a good enough control system it is possible to eliminate this almost entirely, provided the radiator is sufficient and the control system targets are optimized to work together. For example, actual coolant temperature on my daily driver with an electric water pump and good instrumentatation remains within half a degree Celsius of the temperature target, which can range from 106c during cruise to 76c during heavy driving- regardless of whether I'm an hour into a track day, sitting traffic with a heat index of 105f, or idling in a snow storm. The system in that car is actually very similar to what I'm implementing in the x1/9, though the x1/9 will not be getting a heated thermostat so that I can lower coolant temperature on demand, as that's just too complicated and unnecessary.


And yes, "too complicated and unnecessary" is a pretty ironic statement for me to make given what I'm doing with this project....it's just that my limit is a little bit beyond what I am currently planning to do.
 
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Part One: Design

The Fans:

This is where everything comes together- and what makes incredible consistency with this system possible. If you are not convinced about the above design philosophy, hopefully this brings it all together.

The fans will be controlled with radiator outlet temperature, not inlet temperature. This, counterintuitively, allows the system to never have to play catch up. The radiator outlet temperature will be targeted to around 80c. This allows a nice 8 degree difference across the engine (neglecting heat dissipation of tubes, not going to factor that in). The control system will work to keep this temperature consistent- controlling the fans at varying degrees to ensure enough heat is dissipated to maintain the target temperature, regardless of the flow rate through the radiator.

The magic of this, is that through the equation,

Heat Flow Rate = (Specific Heat of Fluid) * (Mass Flow Rate) * (Temperature_outlet - Temperature_inlet)

the fan control system can immediately respond to changes in engine heat load and vary the amount of heat being dissipated, before the coolant that was in the engine has even made it to the radiator yet, unlike the stock system. Hear me out.

Overall system function:

Say you are driving along at steady cruise, and decide to stand on the gas (do you Europeans call it a petrol? :D) and let that 70hp rocket you to some speed marginally faster than you were going.

As you increase the engine output, the heat load to the coolant will quickly change, resulting in a higher engine outlet temperature. In response, the coolant pump will speed up, increasing the flow rate through the engine and (remember, constant inlet temperature) thus bringing the temperature at the engine outlet back down to the targeted value. More heat is being put into the coolant even after the pump speeds up in response, but due to a higher mass flow and not due to different temperatures anywhere in the system. This immediately increases the coolant flow rate through the radiator, and nothing else. As a result, the temperature at the radiator outlet also increases almost immediately, as the water is spending less time being cooled inside the radiator. In response, the fan control system increases airflow through the radiator, dissipating more heat, and bringing the temperature at the outlet back down to the target.

And that's it. Without the coolant that was inside the engine when you floored it even having made it to the radiator yet, the fans are already working harder to dissipate more heat- keeping everything constant except the flow rate of the coolant and the flow rate of air through the radiator. This is not possible with the stock system.

I would like to take the credit for this design philosophy, but I cannot. One of the most technologically advanced automotive cooling systems ever put in a production car (by the Bavarians, naturally) uses this same principle, and in practice the results are second to none. Every six cylinder BMW produced from 2006-2016 uses a system that is nearly identical- with the addition of heat load calculations based on fuel flow rate and the ability to electronically heat the wax cylinder in the thermostat in order to target a temperature below the thermostats natural temperature. On a composite engine like ours (iron block, aluminum head) I don't see an overall advantage of being able to use a heated thermostat to manually swing coolant temperatures by huge margins, as generally speaking, large temperature swings are not great for composite construction engines wherein the coefficient of thermal expansion between the head and block are different. This being said, there are composite engine cars with horrendous engine temp deltas and coolant temp swings that work just fine for hundreds of thousands of miles and many, many years, but just because you can get away with it does not mean you should intentionally cause those conditions, and thus I am attempting to minimize them.
 
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The high incident rate of blown head gaskets and other signs of overheated engines is what makes me think the X can benefit from a more efficient cooling system. Every X engine that I've torn apart had multiple signs of significant overheating, and they were all stock engines in stock Xs. You may blame prior owners servicing practices, or any other excuse. But the incident rate is substantially higher than similar engines/vehicles from other makers of the same era...in my 50 year experience.
 
I don’t agree, so many other 50 year old cars suffer the same. Maintenance is the key, not clever and fancy solutions IMHO, no offence intended. Even a cleverly thought out modern solution applied will fail if the maintenance of the system is not kept up.
 
NEG said:
Maintenance is the key, not clever and fancy solutions IMHO, no offence intended. Even a cleverly thought out modern solution applied will fail if the maintenance of the system is not kept up.
Click to expand...

No offense taken, I'm open to any opinions, though I will back up my own if asked.

To a point, I do agree, but when the stock system is barely adequate in top condition I don't see the point in going to all of the work to restore it just to get sub optimal performance.

I work on systems like this on a daily basis, optimizing them to get every last percent of efficiency and performance out of them...it's simply not in my spirit to go to the effort to make something "meh" again.

When it's done, I will have the best cooling system currently in an X1/9, and if I don't, the project was a failure or someone has done exactly what I plan to do already. The system is fancy and complex, yes, but it offers benefits that a mechanical pump system is simply incapable of providing...not to mention that it'll free up a few HP.
 
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I enjoy doing projects to remake, redesign, reengineer, or otherwise modify things. My intent is to improve the item in my opinion; in some cases its for function, in other cases its for aesthetics, or for any other reason..even if it is just for the fun of doing it. Call me a "tweeker" or "hacker" I guess, but I can't leave anything stock. However there are a lot of things that I believe require improvement out of necessity, especially when it comes to vintage cars. The original designs were not always great even back then, not to mention things have moved on since. :)
 
@NEG makes a good point, there are other 50 year old cars with similar issues. I guess it comes down to what vintage vehicles we have worked on and are familiar with. I can only speak from my personal experience and the vehicles I've enjoyed for many decades, both in this industry and as a hobby. ;)
 
Jonohhh said:
No offense taken, I'm open to any opinions, though I will back up my own if asked.

To a point, I do agree, but when the stock system is barely adequate in top condition I don't see the point in going to all of the work to restore it just to get sub optimal performance.

I work on systems like this on a daily basis, optimizing them to get every last percent of efficiency and performance out of them...it's simply not in my spirit to go to the effort to make something "meh" again.

When it's done, I will have the best cooling system currently in an X1/9, and if I don't, the project was a failure or someone has done exactly what I plan to do already. The system is fancy and complex, yes, but it offers benefits that a mechanical pump system is simply incapable of providing...not to mention that it'll free up a few HP.
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This is where we diverge, I don’t agree the stock system is barely adequate, I think it’s more than adequate if well maintained and adjusted. I will watch this thread with interest though just from an engineering interest point of view to see how you meet your design objectives…good luck! 👍
 
NEG said:
This is where we diverge, I don’t agree the stock system is barely adequate, I think it’s more than adequate if well maintained and adjusted. I will watch this thread with interest though just from an engineering interest point of view to see how you meet your design objectives…good luck! 👍
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Thanks man, I really hope it works out well, too. Of course, I'll keep y'all updated ✌️. I'd be very interested to see how the end product performs compared to a perfectly functioning stock system of a car of the same spec, in the same climate. That'll be the real test- not comparing it to my obviously compromised system.
 
Jonohhh said:
Thanks man, I really hope it works out well, too. Of course, I'll keep y'all updated ✌️. I'd be very interested to see how the end product performs compared to a perfectly functioning stock system of a car of the same spec, in the same climate. That'll be the real test- not comparing it to my obviously compromised system.
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You will want to adjust the cross tube to the no tap version MWB sells and put the heater return between the thermostat and the pump. One could attempt to have the heater return work using the siphon effect of the coolant running past the return on the cross tube but I doubt it will be particularly effective.

www.midwest-bayless.com

Water Pump SOHC Return Tube No Taps (Fiat X1/9, 128, Yugo) - NEW

Water Pump SOHC Return Tube No Taps (Fiat X1/9, 128, Yugo) - NEW
www.midwest-bayless.com www.midwest-bayless.com

NEG said:
This is where we diverge, I don’t agree the stock system is barely adequate, I think it’s more than adequate if well maintained and adjusted. I will watch this thread with interest though just from an engineering interest point of view to see how you meet your design objectives…good luck! 👍
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There is a notable difference between the more temperate climes many of us enjoy and Louisiana which is nigh unto tropical. I tend to agree with you as my experience living in Los Angeles with decently high temperatures I never suffered significant issues with any of my Fiats except for when coming off the highway and immediately being stuck in stop and go traffic when both my X and my 850 would wander into the high temp zone to much consternation on my part.

I autocross my cars, which is a summer activity (which can be quite warm here in west Michigan), one tends to idle for a while waiting for your turn, then a minute and a half of flat out high rpm driving at relatively low speed (and low airflow through the radiator) followed by almost immediate shutdown (or high idle as you try to keep it circulating coolant) with the fan forced on. In my experience the coolant temps during that regime were not nearly what I feel comfortable with. Track time has never worried me as there are always been cool down laps.

So, I can see a need to adjust the function of the pump in particular regimes, particularly for those who are in large urban areas where peak power and then loafing is pretty normal. It is clear that at low engine speeds the pumped volume is barely adequate when there a high btu load that needs to be dissipated. As the mechanical relationship of rpm to pump performance is fixed at all rpms and overdriving it for low rpm performance would likely cause cavitation at the hight rpm.

An electric pump which can be controlled to meet the actual need at any given engine speed and coolant heat load is a reasonable approach in my view. A lot of complexity to be sure and certianly not for everyone :)
 
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