Some cars struggle to keep their cool. In most of those cases, the overheating occurs at low speeds where both air and water flow are at their lowest, such as stop and go traffic or running off-road trails in the heat. Historically, this low speed state could be particularly hard to cool because without the air movement from forward motion, the entire cooling system was engine rpm dependent.
Electric fans overcome much of the air movement problem while dramatically reducing drag on the engine, which is one reason they have been standard on most new cars since the 1990s. However, mechanical belt driven water pumps are still standard, which means they are still engine rpm dependent regardless of the engine temperature. For stock newer cars, this usually isn’t a problem due to extensive testing by OEM manufacturers. However, we build customized classics, hot rods, muscle cars, race cars, and off-road rigs, so things can become a bit more unverified.
Picture this, let’s say you’re stuck in stop and go traffic in a classic car with a built engine or crawling trails at low speed in your 4×4 in the summer heat and you see your water temperature gauge climbing. At these low rpms, the stock mechanical pump will be moving coolant at about four to five gallons per minute (GPM) with no ability to raise that flow rate without revving the engine higher, which also produces more heat. However, if you had an electric water pump plumbed in as a booster, you could have an extra 43 GPM per minute of water flow on tap that would shed a huge amount of heat.
That’s because while airflow gets all the attention, water flow is the true king of cooling. Despite the myths out there, for maximum cooling there’s no such thing as water flowing too quickly through your cooling system. The faster the water moves, the more heat it absorbs. When you slow water down, its ability to absorb and release heat diminishes. That’s because the more time water spends heating up, the less heat it can absorb. Same goes for cooling down in the radiator, if it lingers too long, it doesn’t shed the heat.
So, if you slow down the flow in the cooling system thinking it’ll give the water more time to soak up engine heat, you’re doing the opposite. Warm water is worse at heat absorption, leaving the engine hotter than it should be. And in the radiator, it’s the same deal. Slow flow means the water cools less efficiently, making the whole system work harder. By keeping the water moving quickly, it also ensures the system stays in a tighter temperature range, allowing it to consistently and evenly cool the engine.
What’s the upper limit? There really is no practical upper limit if pressure is kept low enough, and the water pump doesn’t cavitate. Electric water pump manufacturer Davies Craig reports that they have been carrying out research and development on their electric water pumps for years and they have never been able to pump liquid coolant faster and lose cooling efficiency.
We observed the benefit of fast coolant flow at low rpm during testing with our S197 Mustang track car project that we installed a Meziere electric water on. With no controller, the Meziere pump runs at a constant 55 GPM regardless of engine speed. Not only does the engine run consistently cooler under all conditions from street to track, it drops temperature dramatically quickly once we exit our sessions on track since the load on the engine drops, but the water flow stays at 55 GPM.
One quick note about the flow numbers we are using here. These numbers are all based on free flowing tests by the manufacturer, your actual experienced flow rate will be dependent on well your cooling system can move water. For example, a radiator that doesn’t flow well will dramatically slow down overall water flow, as will the presence of a thermostat. Our testbed will be our XJ Cherokee project since we recently upgraded the entire cooling system and added electric fans, and we know it doesn’t have flow restrictions due to aged or clogged components.
In any case, the EWP will absolutely boost low rpm water flow, so if you have an overly hot hot rod, or a 4×4 that just can’t crawl and stay cool, we’re going to show you how easy it is to add an auxiliary electric water pump to just about any vehicle.
(Image/Davies Craig)This little turbo shaped pump is the Davies Craig EWP-150. It weighs about four pounds and can pump 43 GPM of water, which is more than enough to cool down most V8 engines. These pumps can also be used as the sole source of cooling if you want to remove or modify the belt driven pump and have complete control over how hot or cool your engine runs at any time. We’re retaining our mechanical cooling system and adding the EWP as a flow booster. (Image/Christopher Campbell)The inlet of the EWP-150 fits a 1.5 inch hose, or 1.75 with an adapter. It’s also threaded to fit a -16 AN ORB fitting. (Image/Christopher Campbell)While the EWP-150 can be wired to run at full speed whenever it sees power, our kit uses a Davies Craig controller that monitors the temperature of the cooling system and modulates the water pump and electric fans correspondingly. About 90% of total motoring time the EWP will run at 10% of its maximum speed drawing about two amps. (Image/Christopher Campbell)Here’s a look at how the controller modulates the EWP based on the coolant temperature relative to the target temperature. From 40 to 20 degrees below the target temp, the controller will run the EWP for 10 seconds and turn it off for 30 seconds. From 20 to 5 degrees below the target temp, the controller will run the EWP for 10 seconds and turn it off for 10 seconds. From 5 degrees below the target temp to the target temp, the controller will ramp the EWP up to full speed and hold it there until the temp drops. Also note that the controller will turn on the electric fans at 5 degrees above the target temp. (Image/Davies Craig)The backside of the Davies Craig controller conveniently labels all the wires. It’s a very simple install with only a few wires to connect. One drawback is that the controller must be mounted in the passenger compartment of the car; it’s not sealed for use under the hood. (Image/Christopher Campbell)Here’s an overview of the controller wiring layout. Most of the wires run through the firewall and into the engine bay, but the ground can go to the chassis and the 12V ignition source can be from anywhere under the dash. The red 12V wire should go directly to the battery. (Image/Davies Craig)Most of the wiring harness can be lengthened or shortened without issue. This also makes routing the wires through the firewall easier since the plugs can be cut off and reattached. (Image/Christopher Campbell)The temperature sensor is the one wire that can’t be cut. The cylindrical quick disconnect does make it a little easier to route it through the firewall.(Image/Christopher Campbell)If you’re installing the EWP on an XJ Cherokee equipped with the AW4 automatic transmission, there is an ideal plastic plug on the firewall to pass the EWP controller wires through, so no new holes need to be drilled. (Image/Christopher Campbell)We wanted to mount the controller out of the way but still have it handy for monitoring or adjusting. We attached it to the side of our XJ’s console with some heavy-duty Velcro and left extra wire length coiled under the dash so it can be pulled up to the driver seat. The kit comes with a mounting bracket if you want something more permanent. (Image/Christopher Campbell)The EWP-150 kit includes a 1.5 inch (38mm) dual port inline adapter to mount the 1/4 in. NPT coolant temperature sensor. A smaller 35mm adapter is also available, which was needed for our XJ. It’s also acceptable to mount the sensor in a coolant passage in the radiator, intake manifold, or thermostat housing, if you have that option. (Image/Christopher Campbell)An inline coolant sensor like this should be mounted as close to the thermostat housing as possible, but in reality, you’re limited by the shape of the upper radiator hose. We placed it in the only straight section available. Make sure to use Teflon tape on the threads of the sensor and the port plug to seal them. It will be interesting to check the accuracy of our dash gauge vs. the controller. (Image/Christopher Campbell)If you have electric fans, it’s ideal to have the Davies Craig controller regulate them along with the EWP. The EWP kit does not include a fan relay, so you will have to add one or wire it into your current fan relay. In our case, we’re going to use the Mishimoto fan relay on our triple fan system. Rather than override it, we’re going to wire the Davies Craig relay to trigger the A/C override on the Mishimoto so that it takes priority. We’ll raise the Mishimoto controller’s temperature threshold so the two systems don’t fights and leave it as a back up. (Image/Christopher Campbell)The green and black striped fan relay wire on the Davies Craig controller is a ground trigger, but our Mishimoto set up requires a 12V+ trigger. To convert our trigger signal, we’ll wire a standard Bosch relay in this configuration to take the ground trigger and convert it to output a 12V+ trigger. (Image/Christopher Campbell)Locating the EWP itself is probably the most challenging part of the install, but of course it varies greatly from car to car. Here’s the stock lower radiator hose routing in our XJ. It’s snug, but we have a pretty good idea of where we would like to mount the EWP. Technically, you can place the EWP in either the upper or lower radiator hose, but the lower radiator hose is preferred over the upper mostly because the EWP is not self-priming, so air must be bled to avoid premature failure of the seals. (Image/Christopher Campbell)Per Davies Criag, these are the ideal orientations for the EWP and the ones to avoid. Realistically, you’re going to have to work with what will fit in your location, but you should prioritize getting the inlet port horizontal or downward (Image/Davies Craig)We cut the stock lower radiator hose right before the curve goes over the steering box. This section is straight and an ideal place for the EWP outlet. It also tucks up nicely below the power steering pump and doesn’t contact the steering box. (Image/Christopher Campbell)The curves on the other half of the stock radiator hose aren’t going to get the EWP inlet to the radiator. Davies Craig knows this will be a problem for most people, so they provide this lower radiator hose with some very helpful curves. Our plan is to cut it right at the red line and fine tune from there. (Image/Christopher Campbell)Here’s our final routing from the radiator to the EWP inlet. This arrangement fits like a glove with zero interference issues. (Image/Christopher Campbell)Here’s a view showing the orientation of the EWP relative to the power steering pump and steering gear box. It’s snug, but there is no interference. Fortunately, the EWP is light enough that the hoses are more than sufficient to hold it in place. (Image/Christopher Campbell)If you ever need to bypass the EWP-150, but still need your electric fans to operate, the status LED can be inserted into the pump connector as a jumper. This will send a signal to the controller that the EWP is ‘connected’ and the controller will engage the fans at 5 degrees Fahrenheit above the set temperature. Otherwise, the status LED should be mounted inside the car. We tested this function before we got the EWP mounted. (Image/Christopher Campbell)The EWP-150 and controller draw very little power, but if you’re also running three electric fans, plus extra lighting, a stereo system, and other accessories, we highly recommend taking the opportunity to upgrade your alternator or you’ll be pushing your limits. Our voltage was already dropping at idle causing our fans to slow down, so we opted for an ultra-high quality 260-amp MechMan alternator to ensure we have the output to power all our add-ons even at idle. (Image/Christopher Campbell)Each MechMan alternator is tested before shipping. Note that ours is verified to produce 117 amps at 800 rpm and 260 amps by 1,800 rpm. It’s worth noting that before you add one of these high output alternators to your XJ, you will need to do a cable upgrade. The tiny factory wires cannot handle this amperage and will overheat and potentially cause a fire. Our XJ project is already running 2-gauge cables, so we’re good to go. MechMan provides an appropriately sized eyelet to ensure proper connection with the post. (Image/Christopher Campbell)MechMan includes this pigtail for earlier XJ charging systems. Our 2000 does not need this and plugs directly to the alternator. (Image/Christopher Campbell)As with pretty much all high output alternators, a little bit of clearancing is needed on the XJ’s alternator bracket. We used an angle grinder to take a few notches out of the aluminum lower bracket to make room (Image/Christopher Campbell)The MechMan uses an overdrive pulley designed to improve low rpm charging, so the factory belt must be replaced with a belt that is 0.5 to 1-inch shorter. A standard length Dayco 4.0 belt (PN 5060950) for a 4.0 in our 2000 Cherokee is 95.08 inches. Using Dayco’s extremely helpful chart, we found an ideal shorter belt (PN 5060945) at 94.50 inches. You can find this resource here. (Image/Christopher Campbell)We set the Davies Craig controller for 195 and went for a low speed trail run in the mountains around southern California on a warm day with very little breeze. We kept the A/C on the entire time and never got above 10 to 15 mph for about three hours and stopped numerous times to hike around and check out the view. The EWP-150 and the fans cycled on and off perfectly and kept the coolant temp dead on 195 degrees while idling and low speed driving and it never got above 205 during low speed climbing on long hills. Previously, low speed and low wind with higher engine load in warm ambient temperature with A/C running could push our cooling temps to the 215 to 220+ range, even with the upgrade cooling system. If you have a cooling system in good condition and low speed overheating is still a problem, the Davies Criag electric breeze plumbed in as a flow booster may be the answer (Image/Christopher Campbell)
Christopher Campbell has been heavily involved in the automotive world since he began building his first car, a 1967 Ford Ranchero, with his dad at the age of 14. That started a lifelong passion with custom hot rods and muscle cars. After graduating from Cal State Long Beach, he went to work for HOT ROD magazine as Associate Editor. From there he became Technical Editor at Popular Hot Rodding magazine. Currently he creates freelance content for OnAllCylinders as well as many diverse enthusiast magazine titles such as HOT ROD, Muscle Mustangs and Fast Fords, Mopar Muscle, Super Chevy, Mustang Monthly, and 8-Lug.
Comments
2 responses to “Never Overheat Again with a Davies Craig Electric Water Pump”
Hi there, this install is exactly what I have in mind. I already did the Mishimoto install (but with the amazong HD fans) and now there is some additional water flow missing for this capable system.
Why aren’t you using the thermostat in the thermostat housing or one you put between the fins of the radiator?
And 2nd can you tell me what’s the part number of the hose you ordered? All the Best from switzerland/zurich, Michael
Hi Michael,
I’m using the thermocouple that is included with the Davies Craig EWP-150 kit. It allows me to position the probe closer to the cylinder head, so the controller sees exactly what is coming out of the engine.
I’m also still running the 185°F thermostat in the factory housing, but this can technically be removed with the Davies-Craig kit to increase flow. You must remove the impeller from the engine water pump if you do this. Otherwise, there is no control over the flow from the mechanical pump. My current configuration is relying on the mechanical system and using the Davies Craig system as a flow booster.
The lower hose shown is included with the complete EWP-150 kit. I’m fairly sure it’s a V6 Chevy S-10 hose, but I don’t have the part number.
Hi there, this install is exactly what I have in mind. I already did the Mishimoto install (but with the amazong HD fans) and now there is some additional water flow missing for this capable system.
Why aren’t you using the thermostat in the thermostat housing or one you put between the fins of the radiator?
And 2nd can you tell me what’s the part number of the hose you ordered? All the Best from switzerland/zurich, Michael
Hi Michael,
I’m using the thermocouple that is included with the Davies Craig EWP-150 kit. It allows me to position the probe closer to the cylinder head, so the controller sees exactly what is coming out of the engine.
I’m also still running the 185°F thermostat in the factory housing, but this can technically be removed with the Davies-Craig kit to increase flow. You must remove the impeller from the engine water pump if you do this. Otherwise, there is no control over the flow from the mechanical pump. My current configuration is relying on the mechanical system and using the Davies Craig system as a flow booster.
The lower hose shown is included with the complete EWP-150 kit. I’m fairly sure it’s a V6 Chevy S-10 hose, but I don’t have the part number.