Using an EWP as an auxiliary pump to the mechanical

Joel K

Supporter
Russell,

By way of comparison, the SLC radiator core looks to be 2.5”. Seems like you are doing everything possible. A couple questions:

1) Do you have a gap between the fans and the radiator face, even with a shroud a 3/4” gap helps the shroud do it’s job.
2)To me it sounds like your system may have air in it and not fully bled. Most builders recommend a self bleeding setup.
3)Is it possible the EWP is not turning on?
 
Mid engine cars can be very difficult to bleed, I fought overheating for months on my FFR818. If you are struggling with overheating even when moving, then this is the most likely issue and where you should place your focus. If you only have overheating issues when sitting still, focus on fans and airflow.
 

Howard Jones

Supporter
Try it without the thermostat if you are using the controller from DC. The controller effectively replaces the thermostat and reacts much faster than a thermostat to rising coolant temperature. The DC controller is not intended to be used with a thermostat.

Here's what I did with my nostril on my GTD. It seemed to work somewhat.
 

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Russell,

By way of comparison, the SLC radiator core looks to be 2.5”. Seems like you are doing everything possible. A couple questions:

1) Do you have a gap between the fans and the radiator face, even with a shroud a 3/4” gap helps the shroud do it’s job.
2)To me it sounds like your system may have air in it and not fully bled. Most builders recommend a self bleeding setup.
3)Is it possible the EWP is not turning on?
Thanks for the reply. The fan blades are around 1 1/6" off the core. The system is self bleeding but I also have a bleeder at the back of the engine (highest point) and at the top of the radiator. I use both after a refill. The EWP is set to turn on with the fans. They are triggered buy the engine computer and/or the AC when it is on. As the weather is hot ATM the AC is on most of the time. Yes I have checked the pump is actually working and correct rotation. Cheers
 
Try it without the thermostat if you are using the controller from DC. The controller effectively replaces the thermostat and reacts much faster than a thermostat to rising coolant temperature. The DC controller is not intended to be used with a thermostat.

Here's what I did with my nostril on my GTD. It seemed to work somewhat.
Not using the DC controller. Fans are triggered buy the engine computer and/or the AC, when it is on. As the weather is hot ATM the AC is on most of the time. As I still have the belt driven pump running as well I have left the thermostat in with a hole drilled in it as advised by DC. I agree with the nostril mod and think that is the clue to getting air out. Did you add your deeper ones after having overheating issues or did it in the build?
 

Howard Jones

Supporter
Do you have a DC controller? If so let it maintain coolant temp and control fans. How are you turning on-off DC electric pump? If you are waiting for the fans to come on then you are way into overheated coolant before you try and let the electric pump bring it back down. If you are not turning on the EWP through a relay (how are you doing this) then it isn't running at all. Unless it is triggered in parallel with the fans. I don't recommend this method.

Here's my advice. Buy a DC controller (and a separate temp sensor for it) and set it all up so that the DC controller is controlling the electric pump and set its target temp to whatever the engine computer says is normal or slightly below it (10 degrees F or so). Then let the car's computer run the fans if necessary. This way the CD controller will start helping just before the car is full "normal" warm. The DC controller target temp is programmable so you can play with this.

As an alternative, you could install a separate temp sensor and have it trigger the DC pump through a relay. I would select a target on sensor temp for it at just below the engine computer's "normal " running temp. Try 10 degrees F and see how that works. That way the car s mechanical pump will try and regulate the coolant first, then if it goes higher than "normal" temp the DC controller will kick in and help. If all that doesn't work the engine computer will turn on fans.

The second method will only turn the electric pump all on and all off and cycle around your 'normal" temp. The first way using the DC controller is much better because the controller will duty cycle the electric pump to continuously control the coolant temp at the target temp you select.

I did my nostril mod as I was building the car. It was pretty clear that something needed to be done. That was more than 20 years ago. It took me a very long time to get my GT40 to cool properly. When I had achieved that I swore I would never go through that again and run an electric pump if I ever built another car. Thus the DC EWP in my SLC. Works great, I would never use a mechanical pump again. On anything.

Be sure that all the coolant sensors are placed at the hottest coolant spot. This is usually at the place where the water leaves the heads and goes into the thermostat housing. Place all the coolant system sensors together in that spot.

If you want to talk about this, PM me a ph# and time of day in your time zone. I'll see if I can schedule a phone call with you.
 
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Scott

Lifetime Supporter
Russell,

Lots of good advice above. I've spent a fair amount of time trying to make my cooling system as efficient as possible. This is what I've learned with respect to the radiator:

1643159148003.png


I can't figure out how to enter Greek letters, so the following will need to suffice:
  • Q: The amount of rejected heat; this is what you're looking to increase.
  • A: Area of radiator core; this is limited by what will fit, although you can get creative and angle the radiator, use slim side tanks or use multiple radiators.
  • DT: Delta T is the temperature difference between the coolant and the air flowing through the radiator. There isn’t a lot that you can do to affect this DT term (you can affect DT elsewhere as discussed below). However, as you point out, putting an A/C condenser in front of the radiator preheats the air which decreases DT.
  • K: Radiator heat conduction coefficient; this is where a high-quality radiator helps. K will depend on the quality of the material, thickness of the core, the design of the fins, turbulator, etc. Note that while you want laminar flow through much of the cooling system you want turbulence inside a heat exchanger. Why? Because laminar flow results in the fluid in contact with the fins will cool and DT will decrease. Turbulence ensures that hot fluid is constantly in contact with the fins and therefore increases DT. In addition, as coolant flows through a row it cools which reduces DT. Thus, if you were to look at a color-coded heat rejection image it would show a gradient. For this reason, for a given core size, it is preferable to have shorter rows because that results in a higher average DT. This is the same reason why it is advantageous to plumb multiple heat exchangers in parallel rather than in series.
  • M: mass flow rate of air through the radiator.
M is directly related to the mods that you’re currently making. When sitting in traffic M is dependent on your fans and having a shroud with a good seal to the radiator. As Joel points out you want some space between the fan blades and the core. I bought a custom radiator/shroud solution from C&R so I don’t have any insight on how to determine what that space should be.

When the car is in motion M is more complicated. M will be driven by the pressure differential between the front and rear of the core. There are multiple approaches to increase the pressure differential, but in all cases you’ll want to ensure that all air entering the radiator inlet is forced through the core. Many cars, including mine, use a diverging/converging duct. With this approach the inlet is smaller than the core (the air diverges) and the outlet is slightly larger than the inlet, but smaller than the core (the air converges). When air diverges it slows down which increases pressure and when it converges it speeds up which decreases pressure. If you’re wondering how well this works, just look at an airplane wing. The airfoil speeds up the air on the top to decrease pressure.

1643160096569.png

Diverging/Converging duct. The orientation and geometry for a 40 or SL-C would be different, but the concept is the same

If you’re wondering why the outlet is slightly larger than the inlet, the logic is simple. If you’ve ducted properly, everything that goes in must come out. However, the radiator has rejected heat to the air which has expanded it. The outlet’s size is increased to accommodate that expansion.

Before I understood these basics, I would have been inclined to maximize the size of the outlet which might have resulted in the exact opposite of what I intended. This seems to happen a lot to me when it comes to aero

One other helpful tool to improve M is the Gurney flap. You can install one on the leading edge of the radiator outlet to create a low-pressure zone. It would be easy to add a temporary one with a piece of aluminum to see if it helps. If so, it would tell you that you had an issue with mass flow and you could keep it or make other changes to increase the pressure differential.

I have seen some people claim that you don’t want to move coolant too quickly through the radiator because it won’t have enough time to reject heat. This is BS. Yes, it is true that the longer it’s in the radiator the more that it will cool. However, as it cools DT decreases and heat transfer efficiency decreases. When you're above your target temp you want to move coolant as fast as you can short of causing a cavitation problem.

Properly bleeding your system doesn't remove air bubbles created by your system. You may want to consider a coolant swirl pot to deaerate the coolant. They are common on race cars and they are inexpensive (or you can make your own). Carrol Smith states “I still consider the water system de-aerating swirl pot (as described in PREPARE TO WIN) to an absolute necessity on any racing car” and here’s a pic from one of his books:
1643159190597.png


My last point is that the only place where I’ve seen a V presented as “aerodynamic” is for a trailer. Sure, it’s better than a flat rectangle, but that’s a low bar. If possible, put a little round on the V.

I’ve spent a fair amount of effort doing CFD and my car will have a diverging/converging duct with careful ducting, attention to the inlet and outlet sizes and a molded Gurney flap. I'm using a Pierburg brushless pump and a custom expansion tank and coolant swirl pot. Hopefully it all works as intended!
 
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Do you have a DC controller? If so let it maintain coolant temp and control fans. How are you turning on-off DC electric pump? If you are waiting for the fans to come on then you are way into overheated coolant before you try and let the electric pump bring it back down. If you are not turning on the EWP through a relay (how are you doing this) then it isn't running at all. Unless it is triggered in parallel with the fans. I don't recommend this method.

Here's my advice. Buy a DC controller (and a separate temp sensor for it) and set it all up so that the DC controller is controlling the electric pump and set its target temp to whatever the engine computer says is normal or slightly below it (10 degrees F or so). Then let the car's computer run the fans if necessary. This way the CD controller will start helping just before the car is full "normal" warm. The DC controller target temp is programmable so you can play with this.

As an alternative, you could install a separate temp sensor and have it trigger the DC pump through a relay. I would select a target on sensor temp for it at just below the engine computer's "normal " running temp. Try 10 degrees F and see how that works. That way the car s mechanical pump will try and regulate the coolant first, then if it goes higher than "normal" temp the DC controller will kick in and help. If all that doesn't work the engine computer will turn on fans.

The second method will only turn the electric pump all on and all off and cycle around your 'normal" temp. The first way using the DC controller is much better because the controller will duty cycle the electric pump to continuously control the coolant temp at the target temp you select.

I did my nostril mod as I was building the car. It was pretty clear that something needed to be done. That was more than 20 years ago. It took me a very long time to get my GT40 to cool properly. When I had achieved that I swore I would never go through that again and run an electric pump if I ever built another car. Thus the DC EWP in my SLC. Works great, I would never use a mechanical pump again. On anything.

Be sure that all the coolant sensors are placed at the hottest coolant spot. This is usually at the place where the water leaves the heads and goes into the thermostat housing. Place all the coolant system sensors together in that spot.

If you want to talk about this, PM me a ph# and time of day in your time zone. I'll see if I can schedule a phone call with you.
Hi Howard At the moment the water pump control is not a consideration as it is effectively on all the time with the AC and fans. The temp creeps up while standing and runs hot on the highway. It hasn't been hot weather the last few days and I had a clutch hydraulic issue to deal with so more testing required. I think I have improved the highway driving. Yesterday I widened the nostril openings and have added a couple of deflectors without cutting up the nostrils "yet"! I know this is not the best setup but it will hopefully improve air flow. I still think with a 3.2" thick radiator and a 1" condenser in front of that, the issue is air flow through this pair.
 
One thing to note, running the car at 200-215F on track is no issue at all. Clearly cooler is better (to a point) but it will be quite a challenge esp in high ambient temperatures.
 
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