The Serpentine Squeeze – On Your Cooling System

I hope your July 4th weekend was rad and involved good times, good family and of course, good hot rodding.

Up here in the north, where the palatable hot rodding season is short, I finally got a chance to pull my Harley out and take it for a ride. Ahhhh… there is nothing like horsepower to keep your soul fed.

Speaking of July 4th, it’s almost pretty much so hot everywhere. In the south, it’s retched hot. This time of year in Texas and Florida, if you step outside, you just about instantly start on fire. That pretty much so means that if you have A/C on your hot ride, you’re probably clicking it on anytime you get in your ride.

Modern A/C like Vintage Air is a great addition to modern hot rodding. Another great addition to modern hot rodding are serpentine belt drive systems. More and more, customers doing fresh builds are going this route. Like this.

Unless you don’t stand up to pee, you can’t look at this and not think it’s super cool and want one. Fact: looking at machined billet aluminum has been proven to increase male testosterone levels by 500%.

While they look cool, they also are low maintenance. Instead of having to worry about throwing belts like on an old school v-belt setup, they are pretty much so set-it-and-forget-it. Change the belt every couple of years and you will likely never have to worry about it.

However, this is where the benefits can end and the unintended cooling problems begin. Serpentine systems can cause two major problems for cooling your high horsepower ride. The first is kind of obvious, but the second is not so obvious.

Let’s start with the moret obvious problem – clearance. Since serpentine systems use wider belts, they are thicker. They also tend to push the accessories away from the motor and towards the radiator. Which leaves a lot less room for a radiator and fan combo.

What usually ends up getting compromised is the fans. The amount of CFM a fan moves is essentially proportional to how thick it is. More clearance allows space for larger, higher RPM motors and more aggressive blade profiles. In the world of cooling fans, most fans in a certain size (11”, 12”, 13”, 16”, etc.) are available in three profiles:

  • High performance – The highest performing high CFM fans
  • Mid profile – thinner fans, fit in tighter areas but give 35% CFM 
  • Low profile – the thinnest possible fans, typically give up 55% CFM

Thinner profile fans will start to kill off CFM. By a ton. For example, a 2000 CFM 16” high performance fan that is 3-¾” thick becomes a 900 CFM in a 2-⅛” thick thin profile version. Ouch! You will notice that on your temp gauge – big time.

So going to thinner fans is going to KILL CFM on the fans. Fortunately, we have a few magic tricks we use to address these to make your situation coolable.. 

Once again, the cars that have the most issues with this should be quite obvious: those with shoe horned big blocks into places they weren’t intended to be. Or cars that just had really tight clearance to start with.

A few common examples are many of the late 60s and early 70s Mopars big blocks. In the GM world, the 66-67 Chevelle big block cars are also a guilty party in the list of hot rods with serpentine curses. 

However even swaps that should be fine, such as a modern LT swap into a 67 Nova, can be problematic. Because not all serpentine setups are created equal – some keep the accessories nice and tight to the motor. Others move the accessories away from the motor, which tends to be very problematic.

If you’re thinking of a serpentine system, and don’t want one that will cause you cooling nightmares, give Frank or Joe a call (773)599-3067 or drop us an email. We know which ones work well and which ones will be a nightmare.

Another issue with these drive systems is where they place the accessories. Let’s look at our photo again.

From experience, I know this one above is going to be problematic, because of where the tensionser is. On a dual fan setup, it’s going to be smack-dab where the passenger side fan motor is. And it’s going to cause problems. 

Problem number 2 – the much less obvious but the one that will cause you just as much grief as the first. Now, many of the serpentine kit manufacturers feel that as if having a bunch of cool machined billet on the front of your motor isn’t enough. So you need another incentive to justify spending $2500 on an accessory drive.

And what is that? Horsepower. That’s always an easy sell. And how they sell it is by under driving everything by 15-20%. Including your water pump.

We encounter this ALL-THE-TIME. In some ways, I feel like we’re stuck in 1989 with under drive pulleys that added 5 horsepower to your 220HP 5.0L GT Mustang. It’s insane – the LAST thing anybody should be doing on a high horsepower big block motor is underdriving the water pump.

In fact, you want to be overdriving the water pump. 

To verify this is an issue, we’ll have customer’s measure the crank pulley and water pump pulley, then compare results. You can do the same thing in 2 minutes. This is a problem many people with these systems have, but don’t know they have. 

So these are the unintended consequences of running serpentine systems. If you have one of these, or are thinking of buying one, give us a call.

Depending on your car and motor setup, we can recommend which one to buy that will cause the least amount of cooling  issues. Or help you solve a cooling problem created by one of these.

(773)599-3067 speak with Frank or Joe about your project.

Comments 1

  1. Hi Mr Frank this Andre I bought a radiator and fan set yesterday I’m thinking about getting the serpentine conversion kit which one do you recommend

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