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Cooling System Tips - Cool Info For Hot Cars

Don't let your cooling system leave you stranded this summer. Here's how to keep things from boiling over

Doug Marion Sep 6, 2007
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For the record, a V-8's cooling system is the most forgotten and neglected part of any hot rod. We speak from firsthand experience. It used to be that you could replace a factory 195 degree thermostat with a 160, then swap the factory four-blade steel fan for an aftermarket 5-, 6- or 7-blade aluminum or fiberglass fan and be done with it.

While these tricks may help some, the times have changed and the available power levels have increased immensely. We're thinking mainly of the larger and more powerful crate engines that are oh-so-popular, but more and more people are building 700-, 800- and 900-horse street cars. And, not only do they want them to go fast, but they also want them to idle in summer traffic without overheating. Much of this story is meant to be a wake-up call to all of you who plan to install a new, more powerful engine to your otherwise stock Chevrolet.

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Flex-A-Lite's new "Flex-A-Fit" radiators (with optional twin electric fans) have a two-row core in three different core sizes, with inlets offered on either side. There are six different radiator series and sizes.

Think about this: Your stock and high-performance gas-powered V-8 engines create combustion-chamber temperatures of 5,000 degrees Fahrenheit. It gets there faster when it's supercharged, or when the high-performance engine is at full-throttle. The cylinder's "heat energy" produced can be subdivided into 25 percent usable horsepower, 35 percent unusable that goes out the exhaust, and another 10 percent absorbed by the engine oil. The remaining 30 percent of the heat is absorbed by the cooling system-which we have some control over. By controlling the overall design of the cooling system, we are simply attempting to control the "working temperature" of the engine to suit our means.

For the record, your gas engine will also generate about 150,000 BTU of internal heat at 2,500 rpm. Less the emissions particulates, this is enough heat to keep a six-room house a comfy 70 degrees while the outside temperature is 0 degrees. All things considered, the hotter your street engine runs, the more efficient it will be, the more horsepower it will develop, and the less overall emissions it will emit. If your street engine runs too cool, it will eventually create an excessive amount of emissions followed by sludge (from raw gas, exhaust blow-by, crankcase moisture/condensation and related deposits).

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The center of this 350 head gasket and the 350 Monte Carlo it was in saw 12 years of project car use, then it sat idle for 7 years-without enough antifreeze. The coolant's acids silently munched away at the gasket. Upon re-use, water soon entered the number two cylinder. Both head gaskets were then replaced. Had we remembered to use the right amount of antifreeze, we would not have had this problem. All it takes is a small hole in the head gasket to cause major problems.

Excessive cylinder wall taper (from the top half of the engine block being warm from combustion heat, while the lower half is cooler) causes the cylinder walls to wear at different rates, resulting in uneven cylinder wear, and thus decreased efficiency and output.

Engine Coolant
Water has been proven to be the best disperser of heat. Its molecular structure is spaced far apart, which allows large amounts of heat to be absorbed quickly. Unfortunately, water is also highly corrosive to all of the metals within the cooling system. Additives (antifreeze) are therefore mixed in to help correct the water's pH balance to make it non-acidic. Now, the cooling system's metals aren't slowly eaten up and rust is not created. Experts agree that a 50/50 mix of antifreeze and water works best, all things considered. Various manufacturers have introduced extended-life antifreeze. Texaco Havoline's Dex Cool is good for five years or 150,000 miles. Not to be confused with regular green antifreeze, it's colored orange. It might be just the thing for race and show car tow vehicles and for people always on the go.

TIP: Cooling system inhibitors and additives (just like engine oil additives) wear out over time and need to be replaced. It's recommended that the stock coolant be replaced and the system flushed every two to four years, depending on mileage and wear. If the antifreeze is allowed to "wear out" and is not replaced, serious damage to the cooling system and engine will result from rust and corrosion. In addition, the radiator and cooling system can become plugged with depleted additives and inhibitors, resulting in engine overheating and possible serious damage.

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Most electric fans today have foolproof wiring. But you may find some older units out there that can be accidentally wired backwards. Seen here is a test to make sure the puller fan is indeed pulling air through the radiator. We once saw a Pro Street '66 Nova electric fan that was wired backwards. It somehow ran OK in town but it overheated on the highway. Its puller fan was pushing air, causing almost no air to pass through the radiator.

Electrochemical Degradation
Another common problem with all cooling systems, no matter how custom, is electrochemical degradation. ECD, as it is known, takes place whenever a conductive fluid (water, in this case) comes in contact with different types of metals that make up the cooling system. This reaction is caused by the pH balance of the coolant having a higher than normal acidic balance. When the pH balance slips to the acidic side, the acids begin attacking and destroying the parts of the cooling system including the radiator, heater core, water pump, head gaskets, freeze plugs and coolant hoses. This is yet another major reason to replace the engine coolant at least every four years.

TIP: One of the biggest misconceptions about antifreeze is that if some is good, more is better. On the contrary, antifreeze itself does not provide any direct engine cooling benefit; the water does most of that. The antifreeze is there primarily to correct the pH of the water, eliminate freezing and to internally maintain a clean cooling system by preventing the formation of rust, scale and hard water deposits. Because today's factory cooling systems are designed with very small margins of error, even a slightly dirty cooling system will cause overheating. A 10 percent loss of cooling system capacity because of deposits is enough to cause modern engines to overheat, as most have a 195 degree thermostat.

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When engines get too hot they overheat, which can cause head cracking as seen here. This head was Magnafluxed to see if it had any cracks. It was easily welded, then put back into service.

Radiator Pressure Cap
This is a very important part of the cooling system and should not be overlooked. It holds pressure in the cooling system made via heat increase of the coolant. This in-turn raises the system's boiling point. For every pound of pressure present, the boiling point increases 3 degrees. A modern cooling system with a 16-pound pressure cap should have a coolant boiling point near 260 degrees F. Water not under pressure boils at 212 degrees F at sea level. Today's stock factory engines usually operate between 200 degrees and 220 degrees to improve efficiency while also reducing emissions. And with pressurized fuel systems for fuel-injection induction, vapor lock has not been a concern. This 200-plus degree coolant temperature does to a degree enhance the potential of cylinder detonation due primarily to lean fuel mixture, as well as "oxygenated" gasoline.

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Atmospheric Pressure, Radiators, Mechanical Fans & Thermostats
The engine itself is also affected by atmospheric pressure. The density of the surrounding air affects the amount of horsepower potentially available. At sea level, your stock engine has a compression pressure of 256 pounds per square inch after ignition (with 8.0:1 compression ratio). But you just drove to Denver, Colorado, which is 5,280 feet above sea level. The compression pressure is now 194 pounds per square inch after ignition. Then, you drove up Pike's Peak to 14,000 feet above sea level. Your engine's compression pressure is now 120 pounds per square inch after compression. This means your engine is trying to do the same with less than half the available horsepower it originally had at sea level. This makes the engine generate all kinds of extra heat as it's working harder to do less. The water in the radiator will begin to boil much sooner. At 5,000 feet, the boiling point is 201 degrees F, and at 10,000 feet it's 193 degrees F. If you factor in temperature and humidity, it becomes easy to see how the cooling system becomes overloaded. One other heat contributor is airflow, or, to be more precise, the lack of it. Once the heated coolant reaches the radiator, it needs to dissipate immediately. Air passing over the radiator fins makes it happen.

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Speaking of radiators and electric fans, there are many to choose from. Contact the fan manufacturers for their recommendations, do your homework and don't be afraid to ask friends and fellow car club members for their recommendations.

There are at least four important considerations when designing a cooling system:

1. Water pump and its flow rate. You don't want it to be the restriction.
2. Radiator fan. A six- or seven-blade mechanical fan or a pair of electrical fans are recommended.
3. Radiator core. It needs to match your engine and driving conditions by having the correct airflow, correct number of fins-per-inch, as well as large enough internal tube size.
4. Thermostat. It must be able to flow the same amount of water as the water pump-otherwise it'll be a restriction.

TIP: Most factory thermostats flow between 8 to 10 gallons per minute at idle, while high-performance thermostats flow 12 to 14 gallons. How many of you have installed a high-performance radiator and water pump, but kept the stock thermostat? Yeah, me too. It is ultra-important that the pressure between the engine block and the radiator be as equal as possible. The key is to have a top quality, high-performance thermostat.

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TIP: Stant's "Balanced Sleeve" thermostats do not react to sudden changes in pressure. Tests reveal that at high rpm, coolant temperature and pressure can sometimes fight for control of the thermostat. The secret is a balancing seal inside a 1.5-inch sleeve. The seal eliminates the effect of water pump pressure on the thermostat's opening temperature. The result is a thermostat that distributes coolant uniformly at any engine rpm. On computer-controlled engines, a 5-7 percent loss in thermostat performance will change the fuel-to-air ratio, decreasing performance.

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Here is a four-core radiator run for a few years with no antifreeze. Straight water also plays havoc with aluminum and low-grade steel thermostat housings. Follow the directions on the antifreeze bottle. Don't use too much. A 50-50 mix is usually recommended.

Electric Radiator Fans
Electric fans operated by a pre-determined temperature-sending unit or by manual switch have proven to be worthy even on the large-cubic-inch, high-compression engines. They increase the load on the electrical charging system, but they increase engine power by an average of 5-7 hp. (That's the horsepower it takes to drive a standard 4-7 blade fan attached to the water pump and driven by a fan belt. Electric fans also work better/faster during stop-and-go conditions where normal air movement through the radiator is low due to low mechanical-fan rotational speed. Others have stated that electric fans work best at under 40 mph. This is true. Experts also say to mount your chosen electric fan as high up as possible. Why? The hot engine coolant flows into the radiator at the top. In cross-flow radiators that are wider than they are taller, two electric fans in tandem are highly recommended over one big fan.

Electric fan airflow is rated at cfm, but it is unclear if all manufacturers test with the same method. What really matters is how much air is coming through your high-performance 3-4 core radiator with 8-14 fins per inch. When reading up on the electric fan motor, ball bearing motors are said to be the best. They last much longer and require less electrical current to rotate-compared to a motor with bushings instead of bearings.

Most big electric cooling fans today have 10 blades. Note that the "pitch" of each blade is important. The more aggressive the angle or pitch, the more air moved-but the bigger the fan motor required.

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Depending on the manufacturer, or if you might buy a pre-owned electric fan assembly, you may have to fabricate custom mounting brackets for your specific radiator. We overlooked this dilemma many times over the years. For those of you who have no fabricator you rely on, it's good to have a few feet of aluminum bar or soft steel bar laying around, plus a good electric drill, drill bits, plastic tie wraps, nuts, bolts, screws and a bench vice.

Pushers Versus Pullers, Blades
Experts generally agree that puller fans are 20 percent more efficient than pusher fans mounted in front of the radiator. Straight blades are said to be the most efficient, but also the noisiest. "S"-shaped blades are quieter.

A '57 210 Called "Project X"
Back in 1980, I was 36, the oldest of three experienced magazine staffer mechanics working on a yellow 1957 210 post called "Project X" at sister publication, Popular Hot Rodding. A new hot 350 with a Dyers 6-71 supercharger and ported, 2.02/1.60, Turbo heads had recently been installed and raced (high 11s). It was now slated to star in a movie with Tony Danza and Michelle Pfeifer called "Hollywood Knights." I was asked to trailer Project X to the movie location on Van Nuys Boulevard and "wrench" on the car as needed from 5 p.m. to 5 a.m. (the hours the movie was actually filmed). It had a hefty Nash five-speed transmission and a 9-inch rearend with a 5.14:1 ratio with spool.

Tony Danza and I would both drive the '57. He owned a '65 365hp 327 Corvette coupe and took to the '57 like it was his own. To make a long story short, the GMC Roots-type 6-71 supercharger, due to its pumping characteristics, put more heat into the engine than the stock radiator could deal with. After the third "take" on a race against a 427 Cobra, the coolant temperature was 220 degrees F and climbing-ultimately puking coolant onto Van Nuys Boulevard. My next-day remedy was to replace the 9-pound pressure radiator cap with a 16-pounder and install a huge 15-inch diameter electric puller fan to the back of the double-sized, three-core radiator. With twice the number of cooling fins, the '57 soon afterwards got a third member gear change, then a B&M Megablower, and was ultimately driven all over the U.S.-never to overheat again.

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This smart fan manufacturer saw that two large electric fans were mountable-if crooked or offset. It also crafted in rubber flappers to let otherwise trapped air move through the plastic housing. Being extended a few inches, the fans do indeed pull air through the radiator portions not directly in front of either fan.

Flex-A-Lite as a company goes way back, almost as far as I do. I vividly remember buying one of its new fans for my new '66 L79 Nova as a way to increase horsepower. A scant five years later, it was a customer of mine when I worked for an all-cargo airline in Seattle. All the guys and gals I used to know have since retired, but Flex-A-Lite today is bigger and better than ever.

Residing much of the year in Nevada, driving in the hot, arid desert has taxed my 1970 Monte Carlo's cooling system. After 9 a.m., forget it! It had an aged 1970s fiberglass seven-blade mechanical fan in normal West Coast summer weather. But not in the Mohave desert. No way. I decided to invest again in a company that has never ever failed me as a regular paying customer: Flex-A-Lite. Its dual electric fan setup solved my 350's cooling woes and I can drive the car any time of day.

Alumitech Reproductions & Doc's Blocks To The Rescue
We also plan this year to update our "hot" 1970 383/4-speed/4.88:1 Chevelle. It's a non-numbers-matching, fun, work-in-progress street and drag car. It's a fun car to work on too, although it's garaged in arid southern Nevada next to my '70 Monte Carlo. Alumitech offers a choice reproduction aluminum radiator with or without high-performance twin electric fans. Just what the doctor ordered. If your Chevy is highly modified or about to be, or if you drive in sweltering heat, a good source for cooling system and A/C fittings, lines and connections is Doc's Blocks. It has a terrific online super store and it offers a free catalog, too.

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Our Nevada-based '70 Chevelle has a big, heavy, six-blade mechanical fan, which will soon be replaced with an Alumitech aluminum radiator and twin electric fan setup. Also seen is a chrome-plated metal shroud, which is there to keep fingers from contacting the metal fan blades. Don't confuse it with a fan shroud. This setup cannot cool the potent 383 engine. The mechanical fan probably takes 7-8 hp to operate, so we're going to cool the engine and lower the e.t. (by increasing horsepower) at the same time.

Competition Engine Cooling
Over the last 20 years at Orange County International Raceway and Pomona County Fairgrounds, one of the names on Chevys we photographed the most was Meziere. This whole family is high-performance oriented and it also has many championships to back it up.

More recently, we were involved in the buildup of a supercharged, big-block Comp Eliminator dragster when the subject of cooling and race turnaround time came up. In a blink, owner Jerry Shumard uttered, "Meziere!" As both a racer and a shop owner, he knows them very well. Soon thereafter, his blown, big-block dragster was sporting one of Meziere's Extreme Duty electric water pumps. It has never let him down. Meziere Enterprises also specializes in creative, well-engineered cooling system packages. Lastly, they have an electric street water pump that is said to offer better low-rpm and high-rpm cooling with extra horsepower generation. They even offer a 2-year warranty. You can't beat that. With folks like Meziere, cooling problems are a thing of the past.

Most of you know that when trying to cool, much less romp, on an engine during 90 degrees F weather is not easy. Ignoring your cooling system or taking it for granted-even if it is only a few years old-can lead to problems, certain downtime and untimely repairs. We've been there and done that a bunch since 1960. Here's hoping you don't "go there."


Flex-a-Lite Consolidated
Milton, WA 98354
Meziere Enterprises Inc.



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