For as long as there have been internal combustion engines, there have been cooling systems—either air or water cooled. (Air cooled engines aren’t mainstream unless you own a Corvair, VW, or a motorcycle, so we’re not going to talk about them here.)
As the internal combustion engine has evolved, we’ve become versed on how to deal with overheating (and underheating) issues in fluid-cooled engines. In fact—we’ve become better at it in recent decades with better radiators, water pumps, and cooling fans. Solutions have even transcended the cooling system with electronic engine control, improved cam profiles, oil coolers, and even better exhaust scavenging.
Did you know the average engine gives up 75 percent of its heat to the air? Your engine gives it all away via the cooling system, exhaust system, and heat transfer to the air around it.
Yet, the question remains:
Why Do Engines Overheat?
To be effective, a cooling system must give up more heat than it takes on from the engine. To do this effectively, you want sufficient coolant flow through the water jackets, yet at a reasonable speed to where it takes on and transfers enough heat to remain at a constant temperature.
There are many misconceptions about engine cooling yet there’s one basic truth. Your engine’s cooling system is there to do one thing—to extract enough heat to keep an engine happy yet maintain enough heat to keep an engine efficient. An engine’s cooling system has a tricky juggling act of keeping an engine in the 180 to 210 degree F window. That temperature range is achieved with a right-sized radiator and fan combo, along with appropriate water pump speed and coolant flow between engine and radiator.
For engines to operate properly they need a constant temperature range in which to operate.
There are hidden reasons why engines overheat. We’ve seen trash in water jackets from factory machining operations and freeze plugs carelessly knocked inside water jackets during teardowns. Debris in the water jackets will cause overheating. Make sure your water jackets are clear. Incorrectly installed cylinder head gaskets and intake manifold gaskets can cause overheating. Excessive compression ratio and incorrect valve timing can cause overheating. Double check your work.
6 Cooling System Myths & Solutions
Engines overheat or run too cool because we keep making the same mistakes again and again.
Removing the Thermostat One of the greatest cooling system myths is to remove the thermostat to eliminate overheating. Removing a thermostat only adds insult to injury. When coolant never has a chance to give up heat via the radiator it gets hotter and hotter especially if you’re stuck in traffic. Even on the open road, coolant never has a chance to park in the radiator long enough to give up heat energy to the atmosphere. Never operate your engine without a thermostat.
Water is the Best Coolant Another myth is “water is the best coolant.” While that IS true, the caveat here is that water is also the best source of corrosion. Straight water in your cooling system is a bad thing. If you’re running straight water, always add water pump lubricant and a corrosion inhibitor. Also use a coolant enhancer like Water Wetter, which improves surface tension and heat conductivity.
You Don’t Need an Anti-Collapse Spring There are those, including hose manufacturers, who believe you don’t need an anti-collapse spring in the lower radiator hose. Truth—you must have an anti-collapse spring in the lower radiator hose if you have an older vehicle with a conventional cooling system. Because the lower radiator hose channels coolant to the water pump and engine, it is susceptible to negative pressure and collapse at high rpm. The anti-collapse spring prevents hose collapse. Another hose manufacturer states you don’t need the anti-collapse spring because it was used only for factory-fill purposes. This has never been true because there’s positive pressure on the lower hose during fill. Always run an anti-collapse spring in the lower radiator hose.
Fans: More Blades & Faster Rotation When it comes to engine cooling fans, one belief is the more blades you have the better. Another is the faster a fan turns the better. Not completely true. At high speed, the radiator slipstream should be enough to carry heat from the radiator to the slipstream. When air is moving too fast, you get into boundary layer issues where heat doesn’t get carried away because air isn’t actually touching fins and tubes. You want air to move slowly enough across fins and tubes to where it carries heat away. At speeds above 40 mph your engine doesn’t need a cooling fan. Therefore, a thermostatic clutch fan or electric fan works best.
More Fans (Pushing & Pulling) Are Better Some folks believe more fans are better, but this isn’t completely true either. You don’t really need a fan behind the radiator and a fan in front. Ideally you will have a fan or fans behind the radiator that provide cooling capacity based on coolant temperature. If your vehicle needs cooling fans on both sides of the radiator, there’s a way deeper problem than fan capacity.
The Stock Radiator is Good Enough It has been proven the automakers didn’t design enough cooling capacity into factory radiators back in the day. Most had two rows of tubes and not much capacity across their width. Aftermarket four-row core copper/brass radiators improve cooling dramatically. Aluminum radiators do it with fewer rows and wider tubes. What’s more, aftermarket radiators are often identical in appearance to original equipment, which makes them an excellent investment in durability.
Understanding Engine Coolant
When it comes to engine coolant there are a lot of beliefs out there. Although water is the best heat conductor there is, it is not the best choice. Coolant manufacturers often suggest a 50/50 mix of ethylene glycol and water, which will protect your cooling system down to -34 degrees F. If you’re expecting any colder than that, you need a block heater or a warm garage.
Mark Jeffrey of Trans Am Racing in Southern California tells us he runs 100 percent ethylene glycol and no water without consequence and has been doing it for many years. His logic is coolant temperature runs only marginally higher and this approach eliminates any risk of corrosion.
I personally have run 100 percent ethylene glycol without consequence with no overheating, freeze ups, or corrosion based on Mark’s advice. Of course, you can buy antifreeze already mixed with water for the sake of convenience. If you’re going to run an ethylene glycol and water mix, it is suggested you run distilled water to keep minerals out of your cooling system.
There is another coolant option known as Evans High Performance Waterless Coolant (EVN-EVNEC53001). This is the last coolant you will ever have to buy because it is permanent antifreeze. You run 100 percent of it in your vehicle’s cooling system without running water. Begin your Evans regimen with new hoses and cooling system components and a system that is bone dry. If you’re servicing a system with traces of ethylene glycol and water, the Evans Coolant Conversion Kit (EVN-E2197) is the best way to get started.
Hoses, Water Pumps & Other Critical Cooling Components
When you are replacing cooling system components such as hoses, water pump, and thermostat; don’t do it on the cheap. Spend good money on the best components and sleep better. Goodyear Super Hi-Miler cooling system hoses last longer than your average off the shelf hose. And when you couple the Hi-Miler hose with high-quality worm gear clamps you cannot miss when it comes to durability. A trip to SummitRacing.com reveals a wide variety of water pumps for nearly every application imaginable. Regardless of what brand of pump you choose, always opt for a high-flow water pump and be mindful of pulley ratio (pump speed). A water pump that turns too fast moves coolant too quickly through the cooling system, hurting heat transfer.
Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.