How many times have you caught yourself rubbernecking to watch someone pulled to the side of the road, hood up, steam billowing from their engine as they hope to flag down a tow truck? How about at the local racetrack, as a competitor sits helplessly in his overheated car, waiting for a tow back to the pits? The tragedy is that both scenarios could have been avoided if the cars' owners would've taken some quick, easy steps to properly cool their vehicles. Heat kills, and proper cooling of engines, transmissions, and differentials is absolutely vital to their longevity. In this article, we list three popular platforms known for overheating in common circumstances, give some cooling tips for each, and expose some of the newest products designed to safeguard your engine and drivetrain during hot summer months both on and off the race track. Visit the "Tech" section of importtuner.com for two additional commonly overheating rides, and the best ways to keep them cool and making power. If your car's on the list, you can't afford to miss this.
Subaru Impreza STI (GRB)
Late-model ('08-'10) Subaru STIs are notorious for overheating in hot climates due to a number of reasons, starting with the factory hood scoop. Upgrading the factory top mount intercooler to a front-mount intercooler is a good step in cooling charge temperatures, but doing so allows incoming air to flow into the engine bay through the gaping, empty hood scoop rather in the front bumper's inlet, where it needs to pass through intercooler and radiator cores for cooling. To remedy the problem, use a block-off plate or reverse cowl scoop to direct airflow outward, reducing coolant and engine bay temperatures. Late-model STIs are also equipped with a much smaller radiator than any previous Impreza units, including the '92-'00 GC8. Good friend and South Coast Subaru parts manager Ferdie Eng experienced the limitations of the smaller OE core firsthand, when lapping Buttonwillow Raceway caused coolant temperatures to spike to 225 degrees Fahrenheit. Looking for a solution to keep the EJ25's temperatures in check, Ferdie contacted Koyo Radiators for their newest Hyper V Core, engineered specifically for the Subaru STI.
Contrary to popular belief, running a larger radiator doesn't always mean improved cooling. The key to cooling is found in the design of the radiator's fin pitch (number of heat-sinking fins per inch) and overall efficiency (how easily coolant passes through fins, and how much it's cooled in doing so). The Koyo 36mm core, with its high-density fin pitch, catches more air as it enters the core to maximize cooling. The newly offered radiator also comes with a 1/8-inch NPT plug welded on the upper end tank to fit an optional coolant temp sensor, so you don't have to cut your radiator hose and splice one in. Upgrading to the Koyo V Core radiator improved coolant temperatures in the Subaru during a Buttonwillow Raceway track session in 116-degree track conditions. Coolant temperatures remained consistent at 189 degrees throughout the day, with the highest recorded temp momentarily reaching only 213 degrees Fahrenheit.
Subaru OE Radiator measuring 16mm (0.63-inch) in core thickness
This Koyo V spec radiator cut-away (left) shows how its larger sized internal cooling tube
Mitsubishi Lancer Evolution X MR
The EVO X MR equipped with a Twin Clutch SST (sports shift transmission) using a 6-speed dual automated clutch system shares similar transmission gearbox technology used in the Nissan R35 GT-R. The EVO X clutches are hydraulically-operated but are told what to do and how fast to do it via two computers: the ECU, and the Twin Clutch SS-T computer. An example would be while accelerating in 2nd gear, 3rd gear will get preselected with the clutch ‘in’ and as soon as you “slap” the paddle shift. One clutch is opened while the second is closed simultaneously to deliver a quick responding transmission with no interruption of traction when shifting. Unfortunately the transmission has been known to overheating when driven on a race track. Numerous SST owners recall their cars unable to handle more than three hot laps around the circuit before entering limp mode as a “slow down” light on the dash followed by a warning chime would emit, forcing the driver to pit for a mandatory cool down session.
EVO owners, desperate for a fix to overcome their overheating problem during the early manufacturing stages of the car, attempted to modify the factory trans cooler by removing the driver side fog light to increase air flow to the factory core and adding a puller fan to the back side of the cooler. This modification seemed to temporarily mask the problem at hand but proved minimal in improving cooling issues for the already maxed out factory cooler.
Greddy offers a V-mount dual cooler kit using both the existing OE cooler and an additional Greddy core. The Circuit Spec Trans Cooler optimizes air flow to the V-mount kit using an aluminum shroud to filter air into both cores while an additional in-line electric oil pump provides increased oil flow to aid in eliminating heat retention. Extensive track testing at Japans Tsukuba Speedway by Greddy engineers revealed within 16 minutes of racing on the Tsukuba circuit triggered an OE equipped trans cooler EVO X into “safe mode” as temperatures climbed to 140 degrees Celsius (284 degrees Fahrenheit). Additional testing using the Greddy V-mount cooler improved transmission cooling dramatically as test data showed an improvement of 17 degrees Celsius (62.6 degrees Fahrenheit) during a nine minute track session and 39 degrees Celsius (70.2 degrees Fahrenheit) at 16 minutes in comparison to the stock transmission cooler.
Honda engineers provided the Civic with an economical plastic and aluminum/copper/brass radiator that keeps the engine cool while still being lightweight. But over time, dirt, corrosion, and even bits of rubber from hose breakdown can lodge themselves in the radiator, causing the unit to become less efficient and eventually overheat. Equipped with the D-series engine, the Honda Civic uses a half-width, single-core, 16mm (5/8-inch) thick radiator-sufficient for the 102hp DX and 125hp EX, but less than ideal on Civics with engine swaps or turbochargers. Using the factory half-width radiator on a high-output engine at the track can be catastrophic if the radiator isn't efficient enough to dissipate heat. Constant heat being built up in the radiator can cause coolant temperature to skyrocket and the engine to overheat.
Some Civic owners prefer using a half-width radiator to reduce weight, save money, or make space for a custom turbo setup or equal-length header. Upgrading to an aluminum radiator like the Koyo R-Core, with its 53mm (2.08-inch) dual core, allows for better efficiency in dissipating heat from its larger coolant capacity. The Koyo radiator's tubes, fins, end tanks, and brackets are brazed in a state-of-the-art Nocolok furnace, bonding all components to resist damage from vibration, oxidation, and road debris. Road-raced Civics require a much more stout cooling system, due to the extended periods of time spent under hard driving as opposed to the quick spurts of hard street driving or drag racing. For endurance drivers who require the best in cooling, we recommend upgrading the half-width unit to a properly engineered, full-sized radiator that offers more flow capacity and improved efficiency.
Nissan R35 GT-R
On the track, the R35 GT-R is infamous for overheating issues with its twin-clutch transmission. When driven under extreme conditions, high temperatures switch the trans into auto mode, automatically up-shifting to Sixth gear until it has cooled off. After numerous laps around Japan's Fuji Speedway, HKS engineers data-logged the factory R35 GT-R's transmission oil temperature as it triggered a "fail safe" mode at 140-145 degrees Celsius (284 to 293 degrees Fahrenheit). Elevated clutch temperatures also caused the vehicle to automatically switch from all-wheel drive to two-wheel drive, even when the transmission oil temperatures were recorded below 140 degree Celsius (284 degree Fahrenheit).
HKS' recently released DCT (Dual Clutch Transmission) Cooler Kit effectively cools the transmission and keeps oil temperatures low even during prolonged circuit use. Integrated with the factory water-cooled transmission cooler, the DCT Cooler Kit also assists in reducing the GT-R's overall engine coolant temperature.
HKS designed the DCT cooler core to fit within the car's front left fender, and sit enshrouded in a specially designed Fiber Reinforced Polymer (FRP) air duct which directs airflow into it. The transmission's stock heat exchanger and HKS thermostat are integrated into the DCT Cooler, along with a specially designed oil outlet attachment that allows the cooler to stabilize oil temperature in a shorter amount of time than the OE unit. A set of -10 AN oil lines replace smaller factory lines to reduce resistance and increase flow, ensuring proper oil supply to and from the transmission. During testing at Fuji Speedway, water temperature was reduced by an average of five degrees Celsius (41 degrees Fahrenheit), enabling the GT-R to make continuous laps around the circuit while maintaining a constant oil temperature of 127 degrees Celsius (260 degrees Fahrenheit).
Just like other major components in a car, the radiator cannot work on its own. It has supporting parts that help it perform its function more efficiently and among them is the factory fan shroud. Believe it or not, Nissan didn't put in the fan shroud just to take up room or “ugly” your engine bays appearance. The 240SX shroud facilitates the function of the radiator fan as it helps your cooling system to perform at its peak. Many 240SX owners make the mistake of removing their cars fan shroud thinking it doesn’t have an important role in the cooling system or the engine bay would look “cleaner” without it. Removing both the shroud and replacing the stock-pulley driven fan with a pair of electric fan "upgrades" has been known to actually flow much less than the stock fan as it increases the probability of overheating. A properly functioning shroud like the factory piece should be designed to extend all the way past the fan or else it won't pull sufficient air through the radiator. Improper shrouding will cause the fan to pull air from the area of least resistance, which means most of the work the fan does will simply be swirling air around inside the engine compartment rather than drawing cool air through the radiator. Unless your vehicles cooling system is modified, we recommend keeping the factory plastic shroud to prevent overheating, no matter how unsightly in appearance it may be.
Radiator Shootout: OEM VS. Aftermarket
Factory radiators were designed to perform well in daily driven conditions, but have a tendency to fail under strenuous heat cycling and endurance situations. To show the advantages of upgrading to an aftermarket radiator, we conducted a series of temperature tests with an EVO IX using its factory radiator versus a Koyo aluminum radiator to see if upgrading the radiator is a worthwhile investment for most owners. We headed down to HB Speed in Fountain Valley, CA, to make use of their Dynomite data acquisitions dynamometer to datalog coolant temperatures during test runs with each variant installed. Before testing, we set up four high-powered fans and retrofitted two HKS temperature adapters with K-type thermocouple sensors on upper and lower radiator hoses to monitor the temperature of coolant flowing into and out of the radiator. A thermocouple delivers a quicker, more accurate response to rapid temperature changes in comparison to common in-dash water temperature meters.
The EVO was given four hours between each dyno run to completely cool off and was tested using only water, to maintain consistency. HB Speed's Jon Drenas assisted in data logging temperatures on the dyno, and ambient air temperature, cylinder head temperature, and idle temperatures were logged before and after each session.
Pitting the OEM radiator against the Koyo R-Core aluminum unit, our first test commenced with a full-throttle dyno pull to redline. With an ambient air temp of 95-degrees Fahrenheit, the data graph showed the 53mm-thick Koyo aluminum unit displaying a clear advantage over the stocker. Both radiators began testing at 175 degree Fahrenheit, and comparative data between the two radiators showed the aluminum Koyo radiator maintaining coolant temperatures three to four degrees cooler than the OEM unit throughout testing.
The final comparison was an endurance test in which the EVO was spun on the dyno at a constant 4,000 rpm at five pounds of boost for an elapsed time of 60 seconds to simulate a gradient uphill climb. With our Koyo radiator in place, coolant data collected from the upper radiator hose to the cylinder head ran about seven degrees cooler, and coolant entering the engine was four to five degrees cooler than stock.
HB Speed, Inc.
10595 Lawson River Ave.
13401 S. Main Street
GReddy Performance Products
Koyo Cooling Systems