Summer’s Hot Topic: Can Your Cooling System Overcool Your Hot Rod?

Our home office is in the desert of Southern California, a region the locals have designated “The Inland Empire.” Most Americans are familiar with California’s “high desert” area because the Mojave Desert dominates the area. They don’t tell you that the high desert’s heat often pushes west, down the San Bernardino Mountains in the Inland Empire. The blast of warm air is the equivalent of Satan exhaling deeply across the open range for three or four months. We’re talking stupidly hot. Ermahgerd hot!  

Keeping V8-powered cruisers, hot rods, and street machines cool is a real chore, and Southern Californians have become experts in engine cooling system design. In fact, Champion Cooling is located at the undefined western edge of the Inland Empire in Lake Elsinore. Cooling has become such a HOT topic that legendary parts manufacturer Holley Performance Products jumped into the ballgame with its Frostbite line of performance cooling products. We also tapped into Edelbrock’s veteran technical expert, Smitty Smith, for some help. Modern aftermarket cooling products sometimes work so well, we couldn’t help but wonder, could an engine actually be cooled too well? So we went in search of an answer to that very question.

Is Overcooling An Issue?

Almost every automobile’s stock engine cooling system is designed with overcooling capacity for typical daily drivers. It’s when “go-faster” performance parts are added that things can get a little heated. Too much heat is an engine’s worst enemy. Many enthusiasts install high-flow water pumps to help combat heat issues. Others say high-flow pumps move the coolant too fast, causing more of a problem than it fixes. 

… adding excessive coolant flow will cost horsepower to drive it, but not increase cooling capacity. – Smitty Smith, Edelbrock

Too much flow causing overheating is a myth, according to Edelbrock’s, Smitty Smith. “There is a whole lot of science behind heat exchangers, but the bottom line is more flow will never cause a decrease in cooling performance,” he said. “But, there are definitely diminishing returns. Increasing coolant flow is good, but adding excessive coolant flow will cost horsepower to drive it, and not increase cooling capacity.” 

cooling system

High-flow water pumps have helped enthusiasts cool their engines in the modern era.

When asked if a high-flow water pump could cause an overcooling issue, Holley’s Evan Perkins said “Probably not. If everything else in the system is in place and correct, like the thermostat, there’s no reason the engine should not get to operating temperature.”

The fact remains, engine overheating causes damage, which is why so many car builders spend hours designing engine cooling systems that will work well for their car build. Yet, few of these car builders ever consider overcooling or any damage from running too cool. “For a street vehicle, overcooling is not as much of a problem as it is for a performance vehicle. Granted, if your engine is running too cool, it will not be running as efficiently as it could,” said Champion Cooling Systems’ Michael Harding. 

engine cooling

Thermostat – a common culprit of many cooling issues.

About Thermostats

Many experienced mechanics have dealt with Gen I small-block Chevy engines with non-functioning or missing thermostats. This allows the coolant to bypass a temperature regulator (thermostat) and flow directly into the radiator This prevents the engine from reaching normal operating temperature. An engine must reach a satisfactory operating temperature to enhance combustion. The better and more complete the combustion, the more power, and better emissions levels output. “A thermostat provides some resistance in the flow so that the engine doesn’t run too cool,” Harding explained.

Our Experts For This Article

  • Holley Performance Products has automotive enthusiasts covered in the cooling department with a line of accessories by Mr. Gasket and Scott Drake, Weiand Water Pumps, and Frostbite Radiators. Holley and its product lines are among the most respected companies in automotive performance history.
  • Champion Cooling Systems was founded to manufacture high-quality cooling products at affordable prices. This was done to allow more people to enjoy the nostalgia of restoring a classic car. Offering radiators for almost everything driven on the highways in the past 70-years, from American Motors to Willys. If they don’t have it, they can custom make a solution for your application.
  • The Edelbrock Group was created in 2020 with the merging of two performance aftermarket legends, Edelbrock LLC and COMP Performance Group. Both companies represent nearly 130 years of building some of the world’s best-known performance parts for racers and enthusiasts.

What Makes A Good Engine Cooling System?

To understand the issue, we needed to know what makes a good engine cooling system and the theory of how the components work. At the very basic level, there are two types of engine cooling systems: Air cooling and water cooling. Air-cooled engines are typically those engines that are exposed to the outside — like motorcycles and small aircraft. Obviously, air-cooled systems have fewer components and are lightweight. There is no chance of a coolant leak, but these systems are less efficient than liquid-cooled systems

A water-cooled system is more efficient and dampens engine noise by virtue of the water jacket surrounding the cylinders. The uniformed cooling promotes better fuel consumption and a more complete combustion burn. Early car models used a natural circulation of hot water rising to the top of the water jacket where it was passed to the radiator and cooled. The cool water collected at the bottom of the tank and was pushed back into the block’s water jacket by more hot water entering the radiator at the top. 

cooling system

A liquid-cooled system must have a heat exchanger to work properly. This radiator takes hot liquid and forces the coolant through channels where it is cooled by air flow.

Over time, engines got larger and ran higher RPM, and engineers discovered the need to faster circulate water through the engine. By inserting a small engine-driven impeller pump in the water jacket, the circulation rate of the cooling water was improved. The next step was to include a belt-driven centrifugal pump that attached to the engine. This is essentially the system we have today. 

With the addition of a spring-loaded pressure-retaining radiator cap and vacuum valve, the system became the pressurized cooling system that we have in most modern cars. The cap is air-tight so water vapor is unable to escape. The working temperature of the water and engine rise to operating specs, which provides better thermal efficiency. The pressure valve opens when the internal pressure of the system exceeds the predetermined pressure of the valve. This allows the steam to escape and avoid excessive pressure buildup in the system. Once the engine is cooled, the vacuum valve opens and coolant from the overflow tank re-enters the system to compensate for the loss. 

Older And Newer Engine Operating Parameters 

It is no secret that engines in late-model cars tend to run warmer than the vintage iron-block engines from the muscle car era. “With modern engines, a lot of that has to do with alloy compositions of the parts,” notes Perkins. “A lot of these newer engines are 100-percent aluminum, so things expand at different rates. There’s a lot more silicon used in the pistons in modern engines, so they are more thermally stable. They can run hotter and be more efficient without causing problems.

“As we discussed earlier, street vehicles aren’t going to be affected as much by overcooling as vehicles used for racing,” Harding reminded us. “The one problem that running too cool has, is that you don’t get the best efficiency because it will affect your air/fuel ratio and all that. It’s not as much of a problem as it sounds, but you definitely want to get up to operating temperature as soon as you can.” 

cooling system

Modern engine blocks and cylinder heads are more stable in higher temps than ever before.

“For street cars, an engine doesn’t run well at 60 degrees,” said Perkins. “An engine runs well when the cylinder heads are warm and it can actually atomize the fuel to create proper combustion. If you create a situation where it takes excessively long to heat up, the overall driving experience is going to be worse.”

As for the overall operating engine temperature, Harding says, “People need to understand that your engine will get to its operating temperature for the conditions that it is in. Once it gets to a normal temperature range, as long as your engine temperature doesn’t continue to fall or to climb, you really don’t have a problem.” He was quick to point out that “normal temperature” is different for each vehicle. For the sake of assigning a number to it, normal is the coolant temperature when your engine gets to its typical operating temperature. Harding’s vintage muscle car runs at 165 degrees during everyday travel. His daily driver, a modern pickup truck, runs at 220 degrees. 

As long as your engine temperature doesn’t continue to fall or to climb, you really don’t have a problem. – Michael Harding, Champion Cooling Systems

In Summary

“Personally, I’ve never had a problem with something running too cool,” said Perkins. “It has always been the opposite.” Our experts unanimously agree that cooling is based on the engine type and what you are doing with it. There’s no one-size-fits-all for cooling. Each engine type needs a cooling system built for the application. That’s where tips from the pros help out. Anyone can visit Champion Cooling Systems, Holley Performance Parts, and Edelbrock to find cooling solutions for every situation. Check them out and don’t be afraid to call their tech lines. If you would like to read more about engine cooling, you can click here. Meanwhile … don’t be afraid to let the coolant flow!

Article Sources

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
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