Now that warmer weather is here (to be followed by extremely hot temps in the dog days of summer), the chances of your street machine boiling over on the side of the road are increasing daily. It is time to maximize your cooling system.

Prestige Motorsports not only builds engines, but it can supply an entire cooling system.

But exactly how do you maximize your cooling system? There are a lot of factors at play, from the size and construction of your radiator to the fan or fans you use, and a whole lot more. Is your car naturally aspirated or supercharged/turbocharged? Does it have a higher-than-stock compression ratio?

We spoke to Doug Aitken, president of Prestige Motorsports (Concord, North Carolina), a company known for its powerful engine builds and meticulous hot rod construction.

Prestige Motorsports also sells cooling system packages designed to maintain normal temps even in the wildest machines in the hottest weather. The folks at Prestige have seen and heard it all. Making sure your cooling system is up to snuff is like an insurance policy when they sell you an engine — Prestige wants to be sure you don’t hurt the motor they built the first time you take it out.

This 427-inch Windsor is packed tightly under the hood of this 1969 Mustang. Like a lot of restomod projects, it has air conditioning, which adds lots of heat when in use. Prestige Motorsports spec’d out a proper cooling system, from the hoses to the radiator and dual fans to ensure overheating is never an issue.

But it is more than just CYA. It is about getting maximum enjoyment from your street muscle project. There are few things worse than sitting in traffic watching your temp gauge swing for the red zone, while you wonder if you’ll be stuck on the side of the road (perhaps with a wounded engine).

Truth: Horsepower builds heat in your engine. More horsepower means more heat.

If you’ve doubled or tripled the stock number of ponies under your hood, chances are the stock cooling system won’t be up to snuff, especially if your radiator is 50 or 60 (or more) years old.

Prestige Motorsports can go as far as building a custom cooling system for your car that will include everything from the radiator and proper-sized fan or fans, to the intercooler and heat exchanger if your car is super- or turbocharged.

The cooling system’s main components include the radiator, water pump, thermostat, cooling fan(s), hoses, and coolant. The radiator dissipates heat from the engine, the water pump circulates coolant, the thermostat regulates coolant flow, and the cooling fan aids in cooling the radiator. Hoses connect the radiator, water pump, and engine, while coolant is the fluid used to absorb heat.

Some mid-’60s cars like this ’65 GTO with a Tri-Power 389 had virtually no accessories, so a cooling system with a decent-sized radiator and fan shroud was more than adequate. Options such as air conditioning would tax the system, though. (Photo by Jim Campisano)

All those parts must work together in harmony, and they must be sized appropriately to do so. And don’t forget to use the proper radiator cap, which, of course, must be functioning properly.

Burp Your Baby

Doug Aitken, president of Prestige Motorsports, uses this Lisle funnel system regularly to burp cooling systems. It helps ensure there are no air or steam pockets, and accomplishes a complete fill without making a mess.

Aitken  is a big believer in burping your cooling system the right way to get rid of any and all air pockets. They start with a Snap-On vacuum fill kit for starters, then add coolant via a Lisle funnel kit.

Some older readers will not have ever heard of this, so we say watch this video before you proceed:

“We’ve been doing this for 25 years. I feel like what most people were doing (and we did it, too) was you first fire the vehicle up, and the coolant would drop in level, so you kept topping it off, and as soon as that thermostat would open, it comes gushing out and makes a mess,” said Aitken. “Then you capped it, which was bad. It’s been 20 years I’ve been using that Lisle funnel and the main thing is it serves two purposes.

“It’s really there to give you the highest point of fill, so if you’ve got a really weird combination or, say, the manifold is a bit higher than the radiator, well now you put the funnel on there and it becomes the highest fill point. For me, it’s the standard, but unbelievably in the industry, so many people just cap it.”

This Snap-On Cooling System Vacuum/Filler retails for $279, which is certainly not cheap, but it is an invaluable tool.

Aitken has gotten calls from customers who, whether it is one of their engines or someone else’s and they have a fluctuation in temperature or an overheating problem, the first thing he asks is how they filled the cooling system.

This Lisle Spill-Free funnel kit retails for under $50 and lets you burp your cooling system without making a mess.

“Usually, it’s the same thing. ‘Well, I filled it, then I capped it and started it’ or ‘I started it and then as soon as the thermostat opened I put the cap on,’ explained Aitken. “Then I ask did you cap it because it was making a mess, and they’re like, well yeah. That’s the system trying to remove an air pocket.

It is also important to have a coolant overflow tank. Not only is it environmentally friendly, but it will keep you from spewing coolant on the ground on hot days, thus ensuring your system keeps the right amount of coolant in it. (It is also embarrassing, and reflects poorly on your car.) If you ever go to the drag strip, you’ll need one to remain compliant with the rules at most tracks.

Thermostat: Yay or Nay?

This is one of the most highly debated topics. Should you use a 180- , 190- , or a 160-degree thermostat in your street car? Heck, do you even need a thermostat at all?

The answer is an unequivocal “yes” for your street car (even race cars use restrictors for this). Every engine has to have some sort of active temperature control via metering what water that it’s cooled systematically separately from where the water is being heated.

It is, indeed, true that the water will actually flow too quickly through the radiator without one. The coolant needs to be held in the radiator and have some sort of air pass through it to cool it, whether it be through driving or from either mechanical or electric fans. Coolant that does not stay in the radiator long enough does not dissipate any heat, therefore will constantly and slowly heat up until it is just too much. The thermostat regulates the coolant flow through the radiator.

“We use a high-flow thermostat like a Stuart,” said Aitken. “It has a lot more surface area when it opens, and it has bypass holes in it. Those bypass holes help with bleeding the cooling system. I think not running a thermostat is usually you’re doing that to Band-Air some sort of issue.”

Is Your Radiator Big Enough?

Prestige Motorsports does not use a particular formula for picking a radiator; it makes suggestions based on decades of experience. It relies almost entirely on Wizard Cooling Systems for customer builds. A dual core radiator is usually more than capable of doing the job, either with a single 16-inch brushless fan or dual 11-inch small brushless fans. The key is getting a radiator that fits in the core support.

“I always do a brushless fan from Wizard and we’ve never had an issue,” Aitken said.

Make sure your radiator and electric fans will clear your accessory drive. This Mustang got an aftermarket air conditioning setup, which will further tax a cooling system, but it won’t be a problem with this Wizard setup.

A lot of people try to stick with their factory cooling systems, but as we noted earlier if you are driving a ’68 Camaro or a ’55 Chevy, you’re talking about components that are 55-70 years old.

Even if the radiator is well maintained, the possibility of a failure is pretty high. If you have doubled the horsepower of your car, the chances that the factory radiator and fan are going to be able to keep up are slim. In 1993, my daily driver was a supercharged Mustang GT with an automatic and 3.73 gears. The minute we added the blower, the car ran dangerously hot. Adding a high-flow water pump, lower temp thermostat and coolant additive did precious little. The factory radiator was simply inadequate.

That was then. Building a 600-800 horsepower street car today is easier than being distracted by your cell phone. Adding any supercharger to a Gen IV Coyote-powered Mustang or LT1 Camaro or Scat Pak HEMI will net you 750 pump-gas horsepower with proper tuning and no other changes. The stock cooling system on a late-model car can handle these upgrades, but if you are putting said blown Coyote/LT/HEMI into a vintage muscle car, you will need to design your cooling system accordingly.

Putting a supercharged Godzilla into this 1971 Mustang’s engine bay would require a much better cooling system than this car used stock. (Photo by Jim Campisano)

“I could always tell if your cooling system was good or the radiator was efficient if you have an electric fan. Obviously, it will kick on whatever predetermined temperature and most of them will never shut off. If the fan won’t shut off, then that’s basically telling you it is just working its ever-living daylights out to keep it at that temperature,” Aitken said. “If you have a good system, you should hear that thing cycle on and off, or ramp up or ramp down.”

What about the two-row vs. three-row radiator debate? Aitken feels two rows should usually be sufficient —not to mention more efficient.

“Typically, the more cores that you have, they’re smaller and less efficient. More sounds better when you’re talking about horsepower, but cores don’t work the same way,” said Aitken. Traditionally, a good dual inch-and-a-quarter, inch-and-a-half core is perfect. You’ve got lots of surface area for cooling. If you go to a three or four [core radiator], they’re just making the cores smaller and you actually have less surface area of cooling — and you actually have less surface area of cooling, and you have more restriction within the radiator.

“Not to mention if the radiator thickness gets thick, now the fan becomes even more important. If you look at newer vehicles, most of them have a very large single-core radiator because the single core and the thickness of the radiator doesn’t restrict the fan flow so you don’t need a nasty fan on it.

If you are driving a “bottom breather” like a 1968-later Corvette or a third- or fourth-gen Camaro or Firebird, you need as much fan as possible because there’s no air going through the grille. On the plus side, they have a lot of room under the hood, so there’s plenty of room for a good fan and shroud.

And what do you put in the radiator? Aitken and Prestige like to keep it simple: Use whatever the factory coolant is or was. If you are swapping a Coyote or Godzilla, HEMI or LS/LT into a vintage car, Aitken recommends the factory fill. Good old glycol in everything else.

If you race your car and the class prohibits traditional coolant, you are probably using distilled water with an additive, such as Red Line’s Water Wetter or Royal Purple’s Purple Ice, or a product like Evan’s Waterless Coolant.

Fan-Tastic

Then there are your fans. Clutch fans, flex fans, electric fans (brushed and brushless. Factory clutch fans work well, especially at slow speeds, but they do eat up a bunch of power.

“A lot of people throw around numbers. ‘I got 3,000 cfm fans,’ and most of the time, that’s not true. That’s just a marketing number they gave you. SPAL is the best one to use for understanding how much airflow a fan can move. The way they rate it is with static pressure. If you have a draw-through system, which is what we’re typically running — we’re drawing air through the radiator with the fan — and with the static pressure or restriction applied, fans that some would rate at 3,000 cfm move, at best, 1,800 cfm or so. I don’t know how some of the overseas fans are rated, but they are hugely over-exaggerated.”

The Beast is the latest brushless fan from SPAL. It is the most powerful flush-mount brushless fan the company offers. It is a 16-inch, seven blade, configuration.

Aitken continued, “Go to your fuse holder and tell me what fuse is in it. If it’s got a 15-amp fuse, there’s no way. If you have something in a 2000-plus cfm range and it’s a non-brushless fan you would need over a 40 amp fuse, otherwise it would pop at start up.

Doug generally won’t recommend anything but SPAL brushless fans anymore.

So, what is the difference between a brushed fan and a brushless fan? Both designs have their advantages. When it comes down to it, cost is probably the biggest factor. Brushed motors are mass-produced and less expensive. The advantages of brushed motors beyond price are:

• Simple to operate
• Reliable
• Available in many sizes and ratings
• Easy controls
• Good on lower duty cycles

If your application requires a greater level of control and utility outweighs cost, a brushless motor may be the better option. The advantages of brushless are:

• Precise speed control
• Better suited to continuous or long-running duty cycles
• Longer life
• Less maintenance
• High efficiency

For what it’s worth, Aitken generally will only use brushless fans at this point. Wizard Cooling Products‘ fans are all SPAL brushless at this point.

So, are you ready to maximize your cooling system? You still have some time before the real dog days of summer are completely taxing your hot rod’s ability to keep cool.