How To Avoid Fan Wiring That Will Make Your Life Miserable

By now, I hope you understand what it takes to cool your car. With an aluminum radiator, you’re going to want to use a 2-row with 1.0” tubes. And avoid 3-row aluminum radiators (and super-gimmick 4-row aluminum radiators) like the plague.

You’re also going to want to avoid gimmick fans. Even with a good 2-row aluminum radiator, a gimmick fan is going to cause you a lot of grief. These fans tend to be overrated to begin with and will drop off in CFM flow (sharply) as soon as you put a load on them.

So now that you have a good 2-row aluminum radiator and good high powered fans to go with them, you’re going to want to avoid the final gimmick in the cooling system gimmick matrix. Cheap wiring and cheap temperature switches.


When wiring up your fans, you want to use good quality wiring. Especially since we educated you in our last segment about high powered cooling fans. High powered fans draw a lot of amps and therefore need good wiring to support that high amp draw. It’s not exactly rocket science…

However where you can really shoot yourself in the foot, with a really big gun, is by using inadequate wiring. Or using Chinese made wire to wire everything together. Skipping tight to the point, if you are using any of our radiator fan combos, you will want to use a good 10 gauge wire. The reason is simple: using cheap wire will cost you CFMs.


The amount of CFMs that an electric fan moves is proportional to the voltage that it receives. If you lower the voltage, then you lower the CFM that fan puts out. Where most guys go wrong here is they don’t understand how much voltage drop is caused by cheap wiring.


For example, let’s say you have 13.8 volts at the back of the alternator where you pull the power for your cooling fans from. With most wiring kits, you’re going to start with a cheap crimp connector, followed by Chinese 12 gauge wire that’s connected to a Chinese fuse folder. From the fuse holder, you’re going to have another crimp connector through more 12 gauge wire to a cheap relay.

From the cheap relay, you’re going to finally get the power to the fans. The positive current enters the fans and then is grounded through more 12 gauge cheap wiring into a hand crimped ring terminal.


What’s the result of all of this? You end up losing a nice chunk of that 13.8 volts by the time it makes it to your cooling fans. So much so, that only 11.5 volts make it to the fans. That will cut the CFM output of your fan by almost 25%. That’s a ton. That’s why cheap wiring can sabotage the rest of your efforts of using a 2-row aluminum radiator and high powered fans.

Now that we know the wrong way to wire up high powered fans, what is the correct way? The correct way starts with using good wire. We recommend using USA made 10 gauge GXL wire, which is an automotive grade wire designed to stand up to high under-hood temperatures and oil exposure. It won’t melt or degrade over time and become brittle like universal stranded wire from Home Depot.

High quality wire is really important. Most cheap fan wiring kits, even the kits from well recognized names, use cheap wire. Chinese wire is typically made with such poor grade copper and you can effectively drop the gauge rating by a whole level. So Chinese 12 gauge is really more like USA made 14 gauge. And wholly inadequate for use on your hot rod, unless you like grief and aggravation. Chinese wire is also made from cheap silicone jacketing, which won’t hold up to underhood heat.


Another easy way to eliminate voltage drop is to avoid using cheap nylon crimp connectors. A cool trick to convert these cheap connectors into high grade connectors is to remove the nylon sleeve, crimp and solder the connection and then apply automotive grade heat shrink. Not only does it remove resistance points in your electrical system, it also looks 7000% better. You can use this trick anywhere on your hot rod where you need to use crimp connectors and want a pro looking install.

Sticking with the gimmick theme, cheap fan wiring kits usually come with cheap relays. Cheap relays are almost always unsealed, made with recycled Chinese plastic and will cause you lots of grief. These will usually become easily brittle and break, if moisture doesn’t wreck them first.


A high quality automotive relay needs to be sealed to prevent moisture from getting inside the relay and causing corrosion. This isn’t exactly rocket science either, even though our engineer that designed our fan controller used to be a rocket scientist. Well, not exactly but he was an engineer for NASA. As such, we use a sealed enclosure with our fan controller to keep moisture from getting inside and wrecking the relays.


Lastly, there is the temperature switch. A cheap temperature switch will likely cause you more grief than all of the above put together. Why? Well if your fans don’t turn on when they are supposed to, it’s pretty much so a guarantee that your motor is going to overheat.


Chinese temperature sensors are notoriously bad. The Chinese do have some things figured out. They know how to make Iphone cases, the keyboard I’m typing this letter on and even some machined components. However they have a long way to go before they master making engine temperature switches.

They are notoriously horrible and fail often. If you need a good quality temperature switch, it will likely come from Mexico or Turkey (and are really expensive), since there are sadly no companies left in the USA making automotive temperature switches in volume. Even if you can get a hold of a good quality temperature switch, that leaves another problem: they aren’t adjustable. If you want to change the temperature at which your fans come on, you need to buy another temperature switch with a different temperature switch point.

With all of these inherent problems with temperature switches, how do you solve them? The answer is simple: we avoid them all together. By using a sensor instead of a switch, we can avoid all of the inherent problems of temperature switches.

A temperature switch is a mechanical device with moving parts inside, much like a relay. Because there are moving parts inside, it is much more prone to failure. A temperature switch also has to be able to support the current required to close the relay, which is typically 1 amp.

A temperature switch on the the other hand is an electrical device. There are no moving parts inside and it simply provides an electrical signal from 0-5 volts that is proportional to the engine temperature. The first benefit of using a sensor over a switch is they are relatively inexpensive and they tend to last forever. They almost never fail.

Another benefit of using a sensor over a switch is you can easily adjust the temperature at which the fans come on. This is how our fan controller operates. The 5 volt signal from the sensor is fed into our controller where it’s converted to a digital signal. Our controller looks at the dip switch settings and then determines when to turn the fans on or off.

All things considered, there are no good reasons to use a temperature switch over a digital fan controller unless you enjoy lots of aggravation. Even the ‘keep it simple stupid’ argument doesn’t work here, since the wiring involved in using a temperature switch and relays can become a lot more complicated once you add in things like Vintage Air.

How To Avoid The Wimpy Electric Fan Gimmick

In our final post series on giving you a crash course in cooling systems, we’re going to discuss the final piece of your cooling system. Electric cooling fans. Before we do that, let’s briefly review what we’ve learned in our previous posts.

We learned in our previous posts that the real reason why aluminum radiators work better is because aluminum is a stronger material. And because it’s a stronger material, the tubes in the radiator can be made much larger without bursting under pressure.

Because aluminum tubes are larger, fewer rows of tubes are needed to achieve the same amount of cooling surface area. For example, a 3-row copper brass radiator with ½” tubes only has 1-½” of cooling surface area. While a 2-row aluminum radiator with 1.0” tubes has 2” of cooling surface area, even though it only has 2-rows of tubes.

The advantage that aluminum has is fewer rows because there are less tube gaps in the radiator core. Tube gaps are the spaces between the tubes and act like speed bumps that restrict the air as it flows across the core.

So how do electric fans fit into this picture? Let’s start off by talking about CFM rating. When you look at the CFM rating on a fan, they are rated in what is called a no-load condition. That means if the fan was held in the air with no restriction in front of it, that’s how much CFM it would move.

If a fan has a 1500 CFM rating, that means it will move 1500 CFM with restriction in front ot it. Which is a unicorn scenario because when you actually install the fan onto your hotrod, it will have a heavy load on it. That fan has to suck air through your radiator core and your A/C condenser, if so equipped.

This is where the misunderstanding about electric fans comes in. And this is how most people are duped into buying cheap electric fans. A 1500 CFM fan, once bolted to your radiator, is not going to pull 1500 CFM. It’s going to pull a lot less, typically at least ⅓ less. On a typical 2-row aluminum radiator with 1.0” tubes, the actual flow of the fan drops by 30% once it’s installed onto a shroud and mounted to the core.

So that 1500 CFM is only going to pull 1000 CFM once it’s installed on your radiator core.

How can that be? It’s like sucking air through a straw. If you suck on the straw and then suck on it again while you’re pinching it, it’s going to move a lot less air through it.

Using our same 1500 CFM and strapping it a 3-row radiator with ½” tubes, the same fan might only move 700 CFM. Typically, the flow on a 3-row radiator will drop off by 55%. How can that be when the 3-row radiator is thinner than the 2-row aluminum radiator? Let’s review the core thickness details:

3-row radiator: 3-row of ½” tubes = 3 x ½” = 1.5” + 2 tube gaps at 5/16” = 1.5” + ⅝” = 2-⅛” thickness

2-row radiator: 2-rows of 1.0” tubes = 2.0” + 1 tube gap at ¼” = 2.0” + ¼” = 2-¼” thick.

Yes, the 3-row radiator is thinner and is still much more restrictive to airflow, because it has an extra tube gap. These tube gaps are HUGELY restrictive to airflow. I really can’t emphasize that enough.

This is where the fan gimmick can really wreck your summer hot rod experience. Let’s imagine, for a moment that you weren’t one of the well educated hot rodders that read our newsletter. So, you went out and bought yourself a 3-row aluminum radiator. Now to finish off your new radiator purchase, you purchase an accompanying gimmick fan shroud assembly with dual gimmick electric fans. Now you have the Super Gimmick Combo.

Gimmick 3-Row Radiator + Gimmick Fans = Pure Misery

Not satisfied selling just gimmick radiators, the snake oil salesman started selling gimmick electric fans to go with their gimmick radiators. Fortunately, there are some easy ways you can spot a gimmick fan before they lighten your wallet and cause you lots of grief.

The most common gimmick is to over rate the fans CFM. Lots of the big speed part retailers with thick catalogs are notorious for this. However this is quite easy to spot by looking at the current rating of the fan. A good rule of thumb for 12 volt fans is that it takes 1 amp to move 100 CFM. So you have a 2000 CFM fan, that fan should pull 20 amps or more.

Here is an ad from E-bay that we can dissect:

Screen Shot 2016-06-01 at 12.36.56 PM

This ad states that this fan pulls 2500-2800 CFM and only draws 10-13 amps. Doing the math:

2500 CFM / 10 amps = 250 CFM/amp.

Rule of thumb: 100 CFM/amp.

Somehow, this cheap fan on Ebay has managed to defy the laws of physics and move over 2.5 times the rule of thumb. They are either stretching the truth (by a country mile) or they have discovered a new breakthrough in physics that allow them to defy the laws of nature.

I’d sure like to learn this magic trick…

However, I’m going to put my money on they are stretching the truth and selling you a gimmick. In reality, this 2500 CFM fan is more like a 1200 CFM fan. For a moment, let’s assume you weren’t educated and decided to purchase this gimmick fan and strap it to a gimmick radiator.

So now we have a 1200 CFM gimmick fan. From our example above, we can see we are likely to lose about 30% of the airflow when we strap it to a 2-row aluminum radiator with 1.0” tubes. So our 1200 CFM fan is now only putting out roughly 800 CFM. This is with a 2-row aluminum radiator. Now, let’s see what happens when we strap that same fan to a 3-row radiator.

The results are a bit shocking. The 3-row radiator is only going to move less than half of the 1200 CFM and likely only pull 550 CFM. 550 CFM is not enough to cool a 300 horsepower V8. And you’re likely going to find this out the hard way quickly when your motor won’t stay cool.

This might sound extreme, however in reality, we are being conservative with the gimmick fans. They are actually even worse because they are made with cheap electric motors. On a good quality fan with a good quality motor, the RPM of the motor will drop off slightly when it’s placed under a load. On a gimmick fan with a cheap motor, the RPM will fall off HARD when it’s placed under a load. So our example is actually quite conservative.

There we have it. Hopefully we’ve saved you from wasting your time, money and aggravation on the super gimmick combo of a 3-row aluminum radiator and gimmick fan combo.

At this point, you may be wondering if there are any cooling system gimmicks left that the snake oil salesman employ? As it turns out, there is one more that will cause you grief and that’s gimmick fan wiring. We will cover that in our next post.