Upgrading A C3 Corvette Cooling System - Cool It To Use It
One of the most critical and yet overlooked systems to be found on a classic Corvette is the cooling system. Anyone who has clocked any serious seat time in one of these machines has inevitably experienced the anxiety of steadily climbing temperatures, and the worry and grief that goes along with it. Nothing ruins a summer outing like a vehicle that simply won't keep its cool. Add a modified engine, lower gears, or even normal stock equipment like air conditioning, and the potential for heating problems is only exasperated.
With most new vehicles, we tend not to give it a second thought, flying down desert highways in the searing heat of summer, A/C blasting, with nary a worry in a world. Contrast that to sweating with the A/C long switched off to preserve cooling capacity, fretting and concerned as the temperature gauge continues to climb. Sometimes, evasive action is called for, slowing to a fraction of the flow of modern traffic, or even turning on the heater in a desperate bid to shed additional BTUs with the meager capacity of the heater core. Take the opposite scenario, you're trapped in the snarl of urban traffic with nowhere to go, idling and crawling with no possibility of escape; the temperature gauge begins to soar. You suffer the impending doom, again perhaps trying the heater trick, or continuously clutching, or going to neutral and holding some revs in a frantic effort to shave critical degrees. If enough heat reaches the carb, you'll experience the double indignity of an engine boiling the fuel and continually trying to stall. A nightmare scenario? Actually, it's all too common.
These kinds of problems are so prevalent, in fact, that in many cases the tendency to overheat is a primary reason many owners simply will not drive their classic Vette. A few bad experiences as those just described are more than enough for many owners to opt for permanent dry-dock in the confines of a garage. So, what makes a modern machine so capable of coping in situations which may push our older Vettes over the edge? There are a variety of factors, not the least of which include higher overdrive gearing to reduce the revs, and the seldom considered effects of built-up rust and corrosion in the water jackets. Be that as it may, almost all modern machines feature large aluminum radiators with high-efficiency electric fans.
For the ultimate cooling in a classic Vette, it pays to take a page from the advancements put forth by the modern OEMs. First, consider that at best, many older Vettes were marginally equipped in cooling capacity, even when new. Although there are many factors involved in cooling efficiency, such as airflow, the fan/fan clutch condition, thermostat, and water pump, the bottom line comes down to one major factor-the radiator's ability to shed heat. When it comes to real cooling ability, this is the big-daddy factor that really counts the most. If that capacity is not there, you can fool with thermostats, trick water pumps, fans, airflow shields, gaskets, or all manner of magic elixirs and potions added to the coolant, and still come away frustrated. By contrast, bolt-in a radiator with heroic capacity to dissipate BTUs and fans to really move the air, and success is virtually guaranteed every time.
A perfect example of all we've aforementioned is our '76 Stingray. With only a mildly modded 350, this machine has ample get-up and go, but the combination of relatively low gearing and a marginal factory cooling system made it undrivable from any practical standpoint. At normal freeway speed, the temperature would climb precipitously, punctuated with convulsions of boiling and frothing when parked at the end of a run. On the other hand, crawling through traffic was a certain death sentence, sure to end with coolant breaching its confines to spill gracelessly on the tarmac below. Basically, the car was useless, but we knew what to do. Here there was no room to compromise; the plan was simply to bolt-in the best system we could find-a modern high-capacity radiator, complete with precisely controlled electric fans.
Corvette cooling experts at DeWitts have just the items to make all these problems fade to distant memories. DeWitts truly specializes in Corvette cooling components. Although the company sells correctly-detailed restoration cooling parts and radiators for pure OEM restorations, they are famous for their exceptionally capable Direct-Fit replacement aluminum radiators. These units are designed for maximum heat-rejection capacity, while configurations are available for Corvette applications to bolt-in exactly as a conventional OEM radiator. DeWitts pulls no punches and hides nothing when specifying the capacity of these radiators. Their ability to reject heat is given in the appropriate BTU numbers, instead of using vague and non-specific "horsepower" numbers that really give no indication of real cooling ability.
For our application, we ordered a DeWitts No. 73A radiator, which provides a 30-percent increase in cooling capacity compared to a factory radiator, and actually only weighs half as much. This radiator features superior aluminum construction, and has factory-type press-formed end tanks, a dual row-core, serpentine fins, and the factory-type upper-and-lower channels. The beauty of DeWitts Direct-Fit philosophy is the radiator will fit into the stock core support with the original brackets and isolators, and uses the original factory hoses. In an automatic transmission car, the cooling lines thread in perfectly, just like with the original radiator. Absolutely no modifications are required.
Although the DeWitts radiator will work with the original mechanical fan and shroud, we were more than eager to get rid of both, for good reason. The enormous and ungainly factory shroud makes it difficult to work at the front of the engine or suspension, and besides generally getting in the way while in place, it is a bear to remove. There is also nothing really attractive about the factory fan. Its removal promised less power drag, a cleaner, uncluttered look, and better access at the front of the engine. The solution, of course, is DeWitts electric fan setup.
We opted for the top-of-the-line Spal dual electric fan arrangement, complete with the Spal fan controller. While the stock factory fan moves air based on rpm, with some variability provided by the fan clutch, the programmable electric setup is based purely on temperature, and we can't think of anything more logical than that. With the dual fans and controller, the primary fan kicks in at the programmed threshold temperature and begins to run at 50-percent speed. The fan speed increases with temperature, as needed, if the temperature rises. At the programmed upper threshold temperature, the primary fan reaches 100-percent speed, and the secondary fan kicks in to help. As the temperature drops down, the secondary fan cycles off, and the primary slows as needed. All of this happens seamlessly, and the practical result is the temperature remains nearly constant, with more fan capacity jumping in only when needed. With the air-conditioning input wired, both fans will trigger to work at full capacity with the A/C on. Although the fans can be ordered separately and are very easy to mount, DeWitts will mount the fans to the radiator if ordered as an assembly.
So, the bottom line is what did this arrangement from DeWitts do for our Stingray? We got exactly what we hoped for-uncompromised cooling under all driving conditions. While this Vette was utterly unusable with the tired factory cooling system, it has now become our go-to daily driver. We installed a 160-degree thermostat and set the fans to start at 165, with the high threshold set at 190 degrees. The combination of DeWitts' high-capacity radiator and controlled fans keep the temperature virtually constant at about 180 degrees, whether screaming down the freeway at a constant 3,800 rpm or idling endlessly in traffic. In fact, the enormous heat rejection provided by the radiator results in the coolant seldom reaching the high threshold at 190 degrees to call into play the secondary fan.
The fact this cooling system transformed this Vette from a garage queen to a fully functional go-anywhere machine makes it the best modification we could have done, proving that capacity is king when it come to cooling.

Photo Gallery: Upgrading A C3 Corvette Cooling System - Corvette Fever Magazine

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