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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.

In fact, we’ve got an entire article on this subject. Read it here: Evans Waterless Coolant: Better Engine Protection When Things Heat Up

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 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.

Your cooling system is under pressure for a reason—to keep your coolant boiling point as high as possible. You want the highest pressure cap rating suitable for your application. Older vehicles like 7 to 12 pounds. Newer vehicles need more like 12 to 18 pounds. (Image/Jim Smart)
vent recovery tube port on radiator filler neck
Always have some kind of coolant recovery system going. When you vent coolant to the pavement you are putting animals at risk as well as your engine from coolant loss. Antifreeze in any form is toxic and dangerous to animals. They love the sweet taste and it can kill them via kidney failure. (Image/Jim Smart)
engine radiator standing upright alone
The OEM was never much on cooling capacity with two-row core radiators. That’s why a three- or four-row core radiator like this one from Summit Racing Equipment increases capacity without any special modifications. (Image/Jim Smart)
The new radiator is a drop-in replacement for the factory original. (Image/Jim Smart)
Aluminum radiators are popular for motorsports. However, did you know they make terrific drop-in replacements for factory copper/brass radiators? You can leave them in a raw aluminum finish or paint them a satin black and no one will know the difference. (Image/Jim Smart)
Truly the best heat exchanger is a crossflow radiator, which allows for better heat transfer to the atmosphere. Crossflow radiators became more common around 1970 and have been commonplace ever since. Installing a crossflow radiator in a classic vehicle original designed for a conventional flow radiator can be tricky. Never install a radiator metal to metal. Always have some form of soft support. (Image/Jim Smart)
close up of a radiator cap
Radiator caps are available in many forms. (Image/Jim Smart)
person holding a radiator cap
Choose a radiator cap based on pressure and how much pressure is desired. Older cars and trucks like lower pressures in the 7 to 13 pound range. Newer vehicles like 12 to 18 pounds. (Image/Jim Smart)
anti collapse spring inside a radiator hose
The endless debate over anti-collapse springs ends with this: Bottom radiator hoses on vintage vehicles must have a stainless or galvanized steel anti-collapse spring. An anti-collapse spring keeps the lower radiator hose from collapsing at high rpm when the water pump causes negative pressure and hose collapse. If you experience overheating on the highway and normal cooling in town, you need an anti-collapse spring. (Image/Jim Smart)
Thermostat selection depends upon application. Although enthusiasts typically choose a 160 degree F thermostat to treat overheating issues, this isn’t what the 160 degree thermostat was originally conceived for. The 160 degrees F thermostat was originally intended for alcohol antifreeze back in the day. The best thermostat for classic vehicle applications is the 180 degrees F. If you’re experiencing overheating with a 180 T-stat, you have more serious problems—radiator capacity, fan size or installation, or engine related issues such as water pump, compression, a blown head gasket, etc. Late-model computer controlled vehicles mandate the use of a 192 to 195 degrees F thermostat. (Image/Jim Smart)
Opt for the best stainless steel worm gear clamps you can buy. If you’re going racing, double up hose clamps with two at each end of the hose. (Image/Jim Smart)
Coolant filters, installed in the upper radiator hose, are a great idea especially with new engines where iron and aluminum particles can clog radiator tubes. The Gano filter is a good investment in durability and you can see what’s inside. (Image/Summit Racing)
There’s another coolant filter from TRAP, which has to be opened for inspection. If your engine starts running hot over time using a filter, check the coolant filter. (Image/Jim Smart)
brass freeze plugs installed in engine
Always use brass freeze plugs with the deepest dish for best results. Most builders use RTV sealant to secure freeze plugs. Marvin McAfee of MCE Engines in Los Angeles used JB Weld back in the day to secure these plugs. He also opted for screw-in oil galley plugs in all locations. Racing applications get retaining screws at all freeze plugs. (Image/Jim Smart)
Summit Racing carries a variety of high flow water pumps from Edelbrock, Weiand, and other aftermarket brands. Aluminum water pumps save weight and they conduct heat better than iron. Be mindful of forward- and reverse-rotation water pumps. Reverse-rotation water pumps are serpentine belt driven. (Image/Jim Smart)
There are many ways to channel coolant between engines and radiator. The Summit Racing Stainless Steel flexible hose is one of the most durable paths possible for hot coolant to travel and it looks sharp. Installation is simple and it can be done in an afternoon. (Image/Summit Racing)
It is those invisible things we don’t notice immediate that can cause overheating. The word “FRONT” on a head gasket means exactly that. Small block Fords, as one example, are unforgiving of improper head gasket installation because you will block cooling passages. (Image/Jim Smart)
cylinder head gasket laying on engine deck to show coolant passages
Another issue can be MLS composite head gaskets aren’t always happy on older iron head engines. You can run into coolant seepage issues. (Image/Jim Smart)
Here’s another “gotcha!” element: intake manifold gasket installation. Cooling passages must be clear between intake manifold and cylinder heads. Gasket cooling passages must be trimmed in some applications to allow coolant flow. (Image/Jim Smart)
electric fan and radiator in a late model car
Pay close attention to what the factory does in any application. One rule we see broken time and time again is fan spacing and shrouding. In most cases, cooling fans should be shrouded for proper vectoring of air velocity through the radiator. This is a late model Mustang GT with 5.0L power and a factory clutch fan with shroud. Note the fan is half way into the shroud via proper spacing. (Image/Jim Smart
The most efficient cooling fan is the thermostatic clutch fan. It engages only when it is needed and free-wheels when it isn’t. At speed, the fan isn’t necessary. Slipstream air through the radiator handles the cooling. (Image/Jim Smart)
Although this six-blade fan is effective it is also inefficient and noisy. If you’re going racing or live where it gets extremely hot, this fixed-blade fan answers the call of heat. Note this fan is properly positioned half way into the shroud. (Image/Jim Smart)
Pulley ratio is crucial to proper water pump and accessory operation. It is advisable, depending on what type of vehicle you have, to have a 1:1 ratio between crank and water pump pulleys. Check your manufacturer’s specifications for proper pulley sizing. (Image/Jim Smart)
We like this cool accessory drive package from Trans Am Racing for small-block Fords. It is a low-maintenance serpentine belt drive, yet conventional. Note the 1:1 crank to water pump pulley ratio. (Image/Jim Smart)
electric fan on a white surface
Few things beat an electric fan for operational quiet and efficient function. This is a Flex-a-Lite 15-inch 3,000 cfm electric fan for a wide variety of radiators in the 20 inch range. Electric cooling fans should get switched power with ignition on only. Always use a fan relay kit in the interest of safety. These fans pull a lot of amps. (Image/Flex-a-Lite)
Flex-a-lite has expanded its line of direct-fit Flex-a-fit aluminum radiator and electric fan combinations for full-size trucks including the 2004-07 Ford Super Duty F-250 and F-350 with the 6.0L PowerStroke turbodiesel engine. Other applications are available. This is really a nice package that includes a clutch-fan emulator that plugs into the existing control system, sending feedback to the truck ECM and avoiding potential check-engine codes. (Image/Flex-a-Lite)
Flex-a-Lite’s new #185 radiator/fan combo for the 1979-93 Fox body Mustang is a nice twin-fan package you can install over a weekend. The Mustang X-TREME electric fan moves 3,300 cubic feet per minute, draws up to 18 amps and dissipates over 50 percent more heat than competitive 16 inch fans. This guy measures 21-1/2″ x 17-1/2″ x 4-3/16″, covering over 45 percent more radiator surface than the original Mustang fan. (Image/Flex-a-Lite)

Flex-a-lite introduces a solid performance cooling solution for the ’87-’01 Jeep Cherokee (XJ). This new radiator/fan combo featuring a two-row core replaces the stock cooling system without any modifications. When you opt for the electric fans, you get three 10 inch electric fans, moving a total of 2,400 cfm of airflow. (Image/Flex-a-Lite)
fabricated coolant overflow recovery tank
There are plenty of coolant recovery systems available in the aftermarket, so there’s likely one that’s perfectly sized for your car or truck project. We like this compact coolant recovery tank (BCI-70053) from Be Cool. It is easily installed in most engine compartments or you can even hide it in a fender well with easy access for servicing. (Image/Jim Smart)
aluminum coolant recovery tank
This Canton coolant recovery tank can be fastened to your radiator or fan shroud with room to spare. The sight tube makes it easy to check coolant level. (Image/Jim Smart)
Although the Canton CTR-80-231 coolant recovery tank is designed specifically for the Mustang, you can engineer this piece to fit your application. It hugs the fan shroud and is easy to service. This is a 1967-70 Ford Mustang fan shroud for the large 24 inch radiator. (Image/Jim Smart)
If you’re dealing with tight quarters, a universal coolant recovery catch can like this is often an easy install. What’s more, you can install as is or paint/powdercoat to your liking. (Image/Jim Smart)
pouring engine coolant into a radiator from a jug and funnel
One mistake we see a lot out there is either underservicing or overservicing coolant. When you are servicing a cold engine, fill to one inch below the filler neck to allow for coolant expansion as the engine warms. Coolant can rise as much as one inch as the engine warms up. (Image/Jim Smart)
coolant level in a filled engine radiator
Start the engine with the radiator cap removed and coolant one inch below the neck. Then, observe as the engine warms. Allow time for the thermostat to open and for the engine to burp any stray air. (Image/Jim Smart)
jug of evans waterless coolant
Have you tried Evans Waterless Coolant? This is the non-aqueous coolant you will never have to change—ever. Evans Cooling high performance waterless engine coolant is a proprietary base fluid with a specially-formulated inhibitor package designed for all gasoline, light-duty diesel, LP, and CNG engines. It contains no silicates or phosphates, and requires no supplemental coolant additive. (Image/Jim Smart)
pouring evans waterless coolant into an engine radiator
This coolant has a boiling point of 375 degrees F and will not vaporize. The low vapor pressure reduces stress on the engine cooling system components. Evans Cooling high performance waterless engine coolant will also eliminate corrosion and offers protection to temperatures as low as -40 degrees F. (Image/Jim Smart)
Few of us ever think about this aspect of engine cooling, but did you know engine oil is also a coolant? Your engine can run for a time without coolant. It cannot run very long without oil. Not only does engine oil lubricate it carries heat away from the hottest surfaces in your engine. Synthetic engine lubricants are simply better for your engine because they can withstand higher temperatures and last longer between oil changes. (Image/Jim Smart)
Beware of trash in the water jackets of new and remanufactured engines. We’ve seen freeze plugs carelessly left in water jackets by rebuilding operations, which hinders cooling and causes overheating. (Image/Jim Smart)

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Author: Jim Smart

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.