How To Keep Your Classic Corvette from Overheating
Photography by the author and courtesy of Legendary Motorcar
There are few classic cars that conjure up excitement in the same way as a vintage Corvette. Whether it’s a solid axle, midyear, or shark, the idea of thundering down a stretch of two-lane blacktop, wind in your hair, with the sun setting on the horizon, is the stuff dreams are made of. But, if your prized Corvette overheats and dies by the side of the road, that dream can quickly become a nightmare.
Given that even the youngest classic (1953-1982) Corvettes are now almost 30 years old, chances are they need a bit of tender loving care once in a while. And, although it’s not often the first thing that comes to mind, the cooling system should be at the top of the list.
COOLING SYSTEM OPERATION
Coolant circulates through jacket passages in the engine block and cylinder heads, the flow controlled by a water pump mounted on the front of the motor. As it passes through the engine, the coolant absorbs heat. In order to prevent the engine from overheating, the coolant is then directed through a hose into the radiator, where fresh air flowing into the front of the radiator (via fins) cools the antifreeze as it passes through tubes in the radiator (connected to the fins). The “cooled” liquid is then fed through another hose back into the engine, and the process starts all over again.
However, there are a few other components in your Corvette’s cooling system designed to make it work effectively, one of them being the thermostat. This small circular device, mounted near the upper hose on top of the engine, regulates the temperature of the antifreeze. When the engine has just been started and the fluid itself is also cold, a valve on the thermostat prevents the antifreeze from reaching the radiator. Instead, it allows it to circulate, usually via a bypass hose and back through the block and heads, until the engine has reached operating temperature. Once that happens the thermostat opens, allowing the fluid to flow through the radiator, which keeps it cool while the engine is running.
To prevent the engine from overheating, the coolant flowing through it is pressurized via a spring-loaded radiator cap. The cap is designed to regulate pressure in the cooling system, ensuring that it does its job effectively, but also to prevent the pressure from building up too much that it causes parts of the cooling system to fail, i.e., the hoses to collapse. It does this by automatically releasing pressure via a spring-loaded valve, set to a pre-determined level of pressure when the coolant reaches a certain temperature. Excess pressure and coolant is then bled off; on some classic Corvettes such as original fuelie cars and big-block models, the excess coolant is captured in an aluminum expansion tank.
Because there is now less coolant in the engine, a vacuum is created; therefore a secondary valve on the radiator cap allows the excess coolant to be drawn from the expansion tank back into the engine as it cools down.
Besides regulating the temperature of the engine, the coolant or antifreeze is also used to provide heat to the interior. A small radiator-type device found behind the firewall, the heater core, is linked to the engine cooling system by two additional hoses. One allows heated coolant to be drawn into the core, while another returns it back to the block. Once the heat is drawn into the core, it is then, usually via a fan or blower, drawn through ducting into the passenger compartment, heating it. Various doors, in the form of dash-mounted levers, allow the heat to be regulated; for example, a blend door allows heat from the core to be mixed with cooler outside air, while others allow the air to circulate through dash vents to clear the windshield, or heat the cabin. In order to prevent too much heat from entering the cabin, especially on hot days, a heat control valve, located in one of the hoses, blocks the flow of the coolant from the engine to the heater core, often when the Corvette’s air conditioning system is engaged (if the car is equipped with it).
Besides the heater core, another important aspect, particularly as it relates to most classic Corvettes, concerns the fan. All Corvettes from 1953-1982 came from the factory with an engine-driven clutch fan, essentially one that’s driven off the front of the water pump and constantly turns when the engine is running. A clutch drive, mounted on the fan, controls its speed via a viscous coupling, allowing the fan to spin faster at idle to force more air through the radiator, and slower by disengaging direct drive of the fan from the crankshaft when the vehicle is in motion, to reduce parasitic loss. A shroud, usually bolted to the back of the radiator housing, surrounds the fan and is designed to help the blades flow cool air back into the radiator; without it, the fan would just simply spin hot air through the engine bay at idle, and the engine would overheat.
Other critical aspects in a classic Corvette’s cooling system include the freeze plugs (more correctly called core plugs): literally steel plugs that look like lids, which are pressed into the sides of the block when it is manufactured. The plugs fill holes created during the block casting process, where sand that’s used to form the water jacket passages is drained out. Although the plugs are designed to last the life of the engine, if the antifreeze isn’t regularly changed, it can allow corrosion to develop on the plugs causing them to leak, which usually requires removing the engine to replace them.
The water pump is generally one of the most reliable pieces of your classic Corvette’s cooling system. These GM water pumps are mechanical units, using an impeller mounted on a shaft that draws the coolant from the lower radiator hose, into the engine block. Meanwhile, a pulley mounted on the outside of the pump is attached to the belt that’s driven off the crankshaft. A seal on the back of the pump between the housing and the engine block is designed to prevent coolant from leaking as it flows through the pump.
COPPER AND BRASS
Of course, probably the most obvious aspect of any vehicle with a liquid-based cooling system is the radiator, particularly when it comes to classic Corvettes, especially C2 and C3s as we’ll find out shortly. Originally these cars came with copper/brass radiators, the most common type used for passenger cars from the ’20s through the ’80s. These radiators consisted of a copper core, with brass end tanks soldiered on each side. Copper was chosen because it’s a good conductor of heat, as well as being a soft metal to work with, and one that’s easy to repair. Within the core were tubes running from top to bottom, allowing the coolant to flow from the top of the radiator down to the bottom in a single pass, reducing its temperature as it reached the bottom radiator hose. Although the tubes always provide primary cooling, as mentioned earlier, the fins have a role in directing cooler, outside air to the tubes, from the clutch fan or outside air (when the car is in motion).
Early copper/brass radiators contained fairly narrow tubes, but as engines became larger and more powerful, better cooling was required. One solution was to increase the size of the radiator cooling tubes, but doing so actually created cooling dead spots or pockets in the radiator, which affected circulation and actually caused engines to run hotter. GM was one of the first American automakers to address this problem by going back to using smaller-diameter tubes, but in greater numbers. By the early ’60s, this practice was standard on most GM passenger car radiators including Corvettes, but as we shall see, even when new, original style copper/brass radiators could prove problematic on a performance car such as the Corvette, especially as more powerful small-block and (from 1965 onward) big-block V8s took up residence under the hood.
The larger the engine and the faster it spins, the more heat it generates. So, if you’ve got a large performance engine in a relatively small car (say a 1966 Corvette 427), there isn’t a lot of space for that heat to escape. Combine that with a small, narrow grille opening, 40-plus-year-old technology, and a bit of neglect, and it’s easy to see why you’d be reluctant to drive your prized possession more than a few miles, for fear of overheating and cooking your engine. So what can be done to improve matters? Well, as it happens, quite a lot.
Corvette enthusiasts are some of the best served in the marketplace when it comes to restoration and performance parts, even when it comes to the cooling system, so there are a number of ways you can ensure your Corvette runs at its best, and it doesn’t necessarily mean having to fork out for a monster aluminum radiator and dual electric fans, especially if originality or correct appearance is a primary concern. To find out some common cooling issues on classic Corvettes – and the steps to remedy them – we talked to Bob Clemmens at Legendary Motorcar in Halton Hills, Ontario. Bob is the shop’s resident Corvette specialist: a former GM technician who spends his days servicing and fixing some of the most prized muscle cars and exotics in the world.
“A lot of guys will replace the radiator and, if they’re not too concerned about originality, invest in an electric fan, but that doesn’t always solve a lot when it comes to cooling,” he says.
“One of the biggest things is regularly servicing the cooling system, draining out the old antifreeze and replenishing it with a fresh mixture. If you have a vintage Corvette with one of the old-style aluminum overflow tanks, it’s common to forget to drain the entire cooling system; you can get a lot of trapped air, which can compromise the cooling system’s effectiveness; you have to make sure it’s properly bled and when you refill, that the correct level is maintained; these old Corvettes need all the cooling they can get and if you don’t have enough antifreeze in the system, it’s going to be harder to maintain a consistent operating temperature.”
He also says that checking the condition of the radiator and heater core hoses, as well as the fan and drive belts, is also one of the easiest things you can do, but also one of the things that’s most often overlooked. “Because the cooling system is under pressure, any weak links will also affect the ability of the antifreeze to circulate and properly cool the engine. Over time, hoses become brittle and they can crack, causing leaks. Constant pressure also causes them to swell. Take a look at the hoses on your Corvette; if you see them ballooning at one end or they feel soft, or have dry rotted cracks, its time to replace them. It’s a lot cheaper to change a hose than be faced with blown head gaskets or an engine rebuild because the motor overheated because a hose failed.” Belts are less crucial, but should still be checked.
“Technically, as long as the belt from the crank to the water pump is still working, you can still just about drive a C2 or C3 Corvette,” says Clemmens. “But it’s hard to drive it for any length of time without power steering or an alternator, so you should make sure all the belts are in tip-top shape. If the car is an older driver with A/C and the compressor has been bypassed, it can eventually seize from lack of use and you’ll have to dismantle the air conditioning system and replace the compressor, which can work out to be quite expensive, especially if a shop is doing the work.”
Another problem can be a sticking thermostat. If it’s stuck closed, the engine will overheat quickly; if it’s stuck open, it won’t warm up properly. On cold days, that can result in hard starting and stalling, with too rich a mixture that will adversely affect fuel economy and a cabin that won’t warm, because the heater core relies on the temperature of the coolant to deliver heat to the interior. However, if the car runs hot to begin with and is only used on nice, sunny days, sometimes going with a cooler thermostat is an option. “Switching from a 180-degree to a 160-degree unit can help keep your engine cooler on warm days, improving throttle response and power. If the car is an automatic, a cooler thermostat can also be a benefit, since heat is a transmission’s worst enemy,” says Clemmens.
As far as heater cores, they can be another problem area. Over time they can become plugged or corroded and eventually leak, causing the windows to fog up on misty or cold days and the car to run hotter on warm ones, since antifreeze is leaking out of the core and the amount of coolant flowing through the engine and radiator is reduced. If plugged, they can also prevent the antifreeze from circulating properly, which will tax the rest of the cooling system.
However, when it comes to classic Corvettes, Bob says that the C3s can be the most problematic when it comes to cooling, or rather overheating, issues.
“Because of the conventional grille opening, the early solid-axle Corvettes are pretty much like any other Detroit passenger car from the ’50s and early ’60s. Provided the cooling system is in good working order, the radiator is good, belts and hoses are good, the fan is operable and isn’t slipping, and the coolant is drained and replaced regularly, there shouldn’t be any problems.”
C2s, with their angled radiators, can pose a few more problems. The MK IV big-block engines generate a lot of heat, and the angle of the radiator means it’s more susceptible to collecting debris from the road, which can damage the fins and block the flowing of the coolant. “Once that starts to happen, the engine can quickly overheat; the debris collects mainly at the top of the radiator, affecting circulation and not allowing the antifreeze to pass properly through the tubes so it can be cooled. If that happens, the engine will heat up fast, especially at idle, and there’s very little you can do, except turn the motor off and wait until it cools.” Checking to see if the cooling system is maintaining pressure is another one. If the radiator cap can no longer hold sufficient pressure, the car is also likely to overheat.
On C3s cooling is even more critical, largely because of the shape of the nose and the even steeper angle of the radiator. “Third generation Corvettes are probably the least efficient when it comes to cooling,” says Clemmens. “Because you’ve got a small grille area and that steep angle for the radiator, it’s even more important on these cars to make sure the cooling system is in good working order.” And some things to consider might not be that obvious, one of them being the chin spoiler.
“C3s have a small chin spoiler mounted below the valance,” says Bob. “The purpose of this is to direct air from underneath the car and up into the radiator. If the spoiler is broken or missing, then the radiator is basically being starved of cooler air, so even at speed, the temperature will quickly build up.” Another, quite major issue concerns the rubber seals mounted on the top of the radiator.
“With the hood closed on a C3, the idea is to create an almost sealed vacuum for the air to be directed into the radiator, so alongside the chin spoiler, you’ve got rubber seals mounted on top of the radiator, either right at the top of the support, or between the top of the radiator and support,” says Clemmens. “These actually serve an important part in cooling the engine on a C3, as they help cool air reach the top of the radiator. Being made of the rubber, over time they will dry out and become brittle, sometimes they’re even missing. If that’s the case and the radiator is clogged with debris (it’s easily thrown up and gets stuck at the top thanks to the steep angle at which it’s mounted), then you’re going to have problems.”
Another is the fan shroud. It might come as a surprise, but some owners find that it’s often easier to cut the shroud when replacing the radiator. “When a replacement radiator is installed, sometimes a shroud isn’t fitted, or just what’s left of the old one, usually the top part, is used. That renders the clutch fan just about useless, because all it’s doing at that point is rotating hot air in the engine bay, instead of vectoring it into the radiator.”
OE clutch fans can also suffer from fatigue over time. “If the radiator is blocked because of debris, then air pressure builds around the radiator. Because the fan is constantly turning while the engine is running, at speed that pressure can be strong enough that it pushes the fan blades backward and forward, to the point they can crack, sometimes even break off.” Clemmens recalls a couple of specific incidents where he’s seen damage as a result of fan blades snapping off and going right through the hood while the car was at speed.
But what about electric fans: are they a good alternative on a vintage Corvette? Clemmens says yes and no. “Electric fans are now standard on most modern cars, simply because they provide much less parasitic loss, since the engine doesn’t have to turn them. They can be programmed to turn on and off only when absolutely needed, which saves energy and fuel.”
But on a classic Corvette, which originally came with a clutch fan, there’s no denying that electric fans can look like ugly afterthoughts and out of place, especially if the car is largely stock.
“It really depends on the owner and the car,” says Clemmens. “If you’re going to use electric fans and your car didn’t originally come with them, you’re going to have to incorporate them into the wiring.” Some owners will rig up a dash-mounted switch, allowing them to turn the fans on and off. On newer Corvettes, like C4s, C5s, and C6s, the fans are programmed to come on when needed and operate via signals sent from the ECU, relayed through temperature sensors when the coolant gets too hot.
If you’re building a resto-mod Corvette, i.e. you’re using a late-model, fuel-injected crate motor and you’ll be using the wiring harness and ECU, an electric fan is arguably the only way to go, since originality isn’t a primary concern. You’ll also have to think about the power draw. “Installing a modern system with dual electric fans and a shroud will have a much higher amperage draw,” says Clemmens, “so the car’s electrical and charging system needs to be up to the task. If you’re using a stock-style alternator, it likely won’t have the capacity to provide sufficient energy to the battery to power the fan and you’ll likely be suffering from constant charging issues.”
If originality is important, but so is dependability, then the best option is to go with a replacement, factory-style clutch fan. Eaton Corporation still makes them, and they should be available through most Corvette specialists; Paragon Corvette Reproductions is one that did carry them at the time of writing.
“When working correctly – and provided both the clutch and the fan are in good shape – the factory system is extremely reliable,” says Clemmens, “as long as the factory shroud and seals are in place.” Some classic Corvettes, like L88s, came without shrouds, but considering they were primarily built for racing, they weren’t designed for street use. As mentioned above, in order to provide adequate cooling with an original-style clutch fan, the shroud is essential to help circulate air from the fan into the radiator.
But what about radiators – are factory style units adequate, or should you upgrade to a bigger, aluminum aftermarket unit? Clemmens says yes and no. “At the end of the day, it depends on what you want to do with the car. Because many classic Corvettes are valuable, most owners don’t like to stray too far from the OE setup. From my own experience, if you want to drive the car and it needs a new radiator, the best thing to do is either use a new, thicker copper/brass core mated to the existing end tanks or purchase a reproduction aluminum radiator that looks like the factory original.”
Aluminum is most widely used today for radiators because it costs less to manufacture in larger quantities. Although aluminum isn’t as effective at heat transfer, nor as resistant to corrosion, it is less dense and in performance applications where weight savings is of crucial importance, you can employ a thicker radiator with more tubes and fins to aid cooling, in relation to a copper/brass equivalent. For classic Corvette owners, popular suppliers of aftermarket units include DeWitts (which specializes in aluminum radiators for these cars); while companies like Ron Davis Racing can custom-build one to your particular requirements. In terms of availability through vendors, Zip Corvette can supply you with a reproduction aluminum radiator that closely follows the contours of your original unit, and it can even be date-coded to match your particular car.
However, these days going with aluminum isn’t necessarily better. Aluminum radiators, while lighter and capable of packing more cooling capacity within the same dimensions, are also more difficult to repair if damaged and cannot be recycled as effectively as copper/brass units.
Also, given advancements in copper/brass radiator technology, one example being CuproBraze, it is now possible to produce a copper/brass radiator that is much lighter, stronger, and efficient. As its name suggests, CuproBraze uses brazing instead of soldering to join the copper and brass elements of radiators together. Because brazing contains no lead, it results in a lighter as well as stronger bond than soldering, resulting in a much lighter, sturdier radiator; one that’s finally a worthy alternative to an aluminum unit.
As this article went to press, a company out of Pittsburgh called Universal Auto Radiator Manufacturing has started producing CuproBraze radiators designed for OE passenger car use, capable of lasting 100,000 miles or more. Will we see a resurgence of copper/brass units in the collector car hobby? Time will tell, though the indications are that after spending time in the doldrums, the copper/brass radiator is staging a comeback.
Special thanks to Bob Clemmens and Ted Greig of Legendary Motorcar for their assistance with this article.
This might not be the most exciting gauge in the display…
But whether your taste in classic Corvettes runs to a solid-axle car like this 265 powered ’56….
Or a thundering big-block 427 Sting Ray like this ’67 Roadster, one of the most important aspects of keeping it running is a properly functioning cooling system.
Performance engines, like this original 283 fuelie V-8, generate a lot of heat in a small engine bay, so anything you can do to help keep them cool will prove beneficial, including replacing the coolant regularly, checking the belts and hoses, and replacing the radiator and fan if they’re old or worn out.
C1 Corvettes have a major advantage over C2s and C3s when it comes to cooling, thanks to the large, toothy grille opening.
Behind the radiator, all classic (1953-1962) Corvettes feature a steel clutch fan and a shroud to help funnel cool air into the engine, especially when the car is stationary. As long as it’s functioning properly, it’s generally a very reliable setup. Shown is the arrangement on a solid-axle Corvette, in this case a ’57.
On later Corvettes like C2s, because of the radiator location it’s even more critical that the cooling system is properly maintained. That’s particularly true of big-blocks like this ’66 427, where there’s little room for the heat to dissipate. This puts extra stress on the factory radiator, hoses, cap, and water pump.
Due to the rotation of the water pump, heated antifreeze is passed into the radiator from the intake manifold where it is cooled by tubes before returning to the engine. This factory-correct GM replacement hose is virtually new. If the hose looks swollen at one end, or feels soft to the touch, it’s time to replace it.
To prevent the coolant from boiling over, it’s pressurized with a spring-loaded radiator cap helping to maintain that pressure. If the cap can no longer do so, the engine will quickly overheat, with steam and antifreeze escaping through the top of the cap.
On C2s, a fairly narrow grille opening below the headlights helps direct cool outside air into the radiator. However, given that it is small, you want to make sure the grille and the radiator are kept free from debris or obstructions, to ensure adequate airflow.
As traditional ethylene glycol/water-based antifreeze ages, it changes composition. Over time it becomes acidic, which can actually cause it to start eating away at some engine parts, particularly aluminum components such as thermostat housings, intake manifolds, and cylinder heads. This will result in leaks and can lead to a major engine rebuild.
The clutch fan is mounted on the front of the water pump assembly, and is driven from the engine crankshaft via a rubber belt. If the belt snaps and the fan stops rotating, on a C2 the engine will quickly overheat, especially at low speeds.
The factory radiator shroud is a common cooling issue on older Vettes, says expert Bob Clemmens. When many of these cars are serviced and the radiators are repaired or replaced, the shrouds are often damaged or not put back in.
Here’s another view of a C2 Corvette grille – you can see just how small it is. Because the frontal area is relatively small, the radiator on these cars is set on an angle to help maximize airflow, but that also makes it more vulnerable to clogging from foreign objects, especially at the top.
Another problem area can be the heater core. Antifreeze flows from the engine into the core, and back out via these outlets. If the heater core becomes blocked, or begins leaking, it will affect coolant circulation, putting additional pressure on other parts of the car’s cooling system.
This view of a big-block 427 shows the bypass hose that circulates the antifreeze back through the engine instead of sending it to the radiator when the motor is cold. Seals on the water pump can become brittle over time, causing coolant to leak, so checking the water pump should be part of your regular cooling maintenance schedule.
Here’s a typical vintage GM water pump. Like most aspects of classic Corvettes, it’s a mechanically driven unit, off the crank via a belt. An impeller mounted in the back pushes the antifreeze from the bottom of the radiator, back into the engine through passages in the block and cylinder heads, before it makes its way back to the radiator.
If you’re using traditional antifreeze, corrosion can actually cause deposits to form in the antifreeze. These deposits attract heat, raising its temperature and causing flow blockages through the jacket passages and the water pump.
Out of all the classic-era Corvettes, third-generation cars are generally the most susceptible to cooling issues. Pictured is a ’73 Stingray.
This particular car is a good example of a C3 “driver.” It’s powered by a small block 350 V8 but sports a few upgrades, including an electric cooling fan. However, although it starts and runs, it was suffering from a few cooling issues.
In this picture, you can see that the angle of the radiator in a C3 is even steeper than those found in second-gen Corvettes. “That means it’s even more prone to damage or blockage from foreign objects,” says Clemmens.
On C3s, when the hood is closed small rubber seals mounted on the top half of the radiator help direct cool, outside air into it. Being made of rubber means that they will eventually dry out and become brittle, sometimes even breaking. That was the case on this ’73, which certainly wasn’t helping when it came to cooling issues.
Having removed the radiator cap, we inspected the coolant level. It was at the full mark, but we still weren’t satisfied.
So we decided to test it to see if it was still safe to use.
Our results indicated that it was still within spec, with a freezing point beyond -40 F. Another good idea is to test the acidity of the antifreeze using pH test strips. If the pH level is below 7.5, the mixture is becoming increasingly acidic and needs to be changed. As a general rule of thumb, you should replace ethylene glycol antifreeze every two years.
Some antifreeze mixes already come formulated like this. If you have one that requires mixing with water, it’s best to use distilled water to minimize corrosion and lime scale buildup in your car’s radiator, water pump, and jacket passages.
Before deciding to replace the radiator or fan, it’s a good idea to test the radiator cap to see if it’s maintaining pressure. On our ’73, because it was suffering from cooling bothers and we hadn’t yet pinpointed the problem, we decided to do just that.
Using a pressure tester (available from most auto parts stores), we found out this was the root cause of our cooling problem. Because the cap could not maintain adequate pressure, it was causing the antifreeze to exceed optimum temperature, which led to the engine running hot.
And here’s why: the rubber seals on the bottom of the spring base had degraded, preventing the cap from sealing. So it was tossed and a new, replacement cap was installed.
Although the radiator in C3s isn’t particularly accessible, you can inspect its condition by opening the hood and peering through the gap between it and the front valance. Debris tends to collect at the top of the radiator, and damaged or bent fins can severely hamper cooling. On this one, only minor damage was observed.
C3s also use a small, under-nose chin spoiler to help direct cool air into the radiator. However, the location of the spoiler means that it’s easily broken, often from curb damage. If that’s the case, the radiator can’t effectively harvest air from outside when the car is at speed. Replacing the spoiler, if it’s missing or damaged, should be a priority.
On this big-block C3, you can see that the rubber seals are mounted under the radiator top support instead of above it. You can also see the seal at the front of the hood, which helps create a spoiler effect for the air when the hood is closed. Unlike those on the ’73 illustrated previously, these seals are in good shape, meaning that as long as everything else is functioning correctly, cooling should be adequate on this particular car.
Because antifreeze expands as it heats up under pressure, at a certain point it has to be released to prevent parts of the cooling system from failing, such as the hoses collapsing. Consequently, a relief valve in the radiator allows the excess to be bled away. On some vintage Corvettes and virtually all modern ones, that excess is captured in an expansion tank (shown here in original aluminum form). When the engine is switched off and cools down, the excess antifreeze is drawn back into the radiator. When flushing the antifreeze on a Corvette equipped with one of these tanks, it’s vital that the entire system is bled; otherwise, residue left in the tank can cause air pockets, which will affect cooling.
Back when they were new, road testers, particularly Car & Driver’s Steve Smith, complained of cooling problems on big-block C3s, so if you own one of these cars and drive it even sparingly, you need to pay special attention to the cooling system. This 435-horsepower 427, installed in a ’69 Stingray roadster, sports tri-power induction, ranking this particular car as one of the most desirable Corvettes in existence.
Until the ’80s, most cars, including Corvettes, used copper/brass radiators. Copper was chosen because it’s relatively abundant and also a good conductor of heat. On most automotive radiators from this era, brass end tanks were soldered to each end of the core. Today, original-style copper/brass radiators are still available, but if you intend to drive your Corvette any long distances, looking at a modern aluminum radiator or thicker copper/brass unit is probably your best option.
Inside the radiator are tubes, which allow the antifreeze to cool as it passes through them. Small fins on the outside help direct outside air to the tubes, to provide secondary cooling. If a sizeable number of the fins are damaged or clogged, it will hamper airflow to the radiator, which means it’s time to replace it. In this picture you can see a few fins are already showing signs of damage.
If the radiator is old, it can be suffering from serious corrosion or lime scale buildup, as seen here. That means that some of the tubes are clogged and it can no longer function properly, and needs replacing. This one came out of a car that had apparently been “restored.” It proves that when buying any classic car, including a Corvette, you need to examine the car very carefully.
Another problem with original OE copper/brass radiators fitted to Corvettes and many other now classic cars, was that the number of tubes to provide cooling was rather limited, and the cores themselves relatively narrow.
An increasingly popular option today for many classic car owners, if they want to drive the vehicle but maintain a correct look under the hood, is to use a thicker three or sometimes even four-row radiator core, mated to the stock end tanks. That way you get better cooling, while maintaining an original outward appearance. This radiator had just been re-cored and returned from a radiator shop when this picture was taken.
On classic-era Corvettes, the engine-driven fan uses a viscous coupling clutch to disengage direct drive from the crankshaft. This allows it to spin more slowly to funnel more air into the radiator, especially when the engine is turning faster. Over time however, the clutch wears out and starts to slip, eventually causing it to freewheel. You can tell if the clutch is worn out by grabbing the fan and rotating it when the engine is shut off; if the fan rotates freely, it’s time to replace it.
Another common problem on classic Corvettes concerns the fan blades. If the radiator is blocked, it can cause pressure buildup between the radiator, fan, and shroud. As the fan turns, the blades are pushed forward and backward by the excess pressure; to the point that fatigue will set in and they’ll eventually crack. In some cases blades can even break off while the car is at speed, causing a real mess. Checking the condition of the blades should also be part and parcel of regular cooling system inspections.
The thermostat is another item to check before splurging for a big fancy radiator or electric cooling fan. If it’s old, sometimes the thermostat will be stuck closed, not allowing the coolant to flow into the radiator. If that’s the case, as soon as the engine reaches operating temperature it will likely overheat.
Installing a cooler thermostat can be beneficial, especially if the car is a summer day pleasure driver. Going with a 160-degree unit can help the coolant circulate faster through the system, lowering the operating temps. It’s one trick to think about, especially on Corvettes that have marginal cooling to begin with, like original big-block cars.
Provided regular maintenance is performed on the cooling system, this is where you should be spending most of the time in your classic Corvette, not under the hood trying to fix it.
DeWitts 517-548-0600 www.dewitts.com
Legendary Motorcar Company Ltd 905-875-4700 www.legendarymotorcar.com
Mid America Motorworks 866-350-4540 www.mamotorworks.com