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.