Oil does its best work within a specific temperature range. Too cold? Low flow problems. Too hot? Metal to metal game over. Cold engine startup is no time to get rev-happy and the hot end of the oil temperature spectrum is a danger zone of accelerated wear or outright engine destruction. Oil can run a little hotter than coolant but protection decays rapidly as temperatures climb. Enter the oil cooler. Factory-issue oil coolers do the job for factory-issue driving. Bumping up performance or towing heavy loads can not only create excessive heat in the engine but also down the powertrain line into transmissions, differentials and power steering.
Battered late-Eighties factory off-road heavy-duty oil cooling from Mitsubishi with plenty of room for improvement with a universal oil cooler like this fin and plate unit from B&M.
Engine Oil Control
Drivers of vintage Porsches and riders of air-cooled motorcycles already know that oil and air not only keep the engine cool but also prevent it from eating itself up. Consistent performance is an added bonus to longevity. The air-cooled VW crowd has long used external mount oil coolers to keep modified air-cooled flat-4 engines alive on Baja runs or slow uphill microbus crawls. Race cars bristle with oil coolers. The factory-issue oil cooler is making a comeback thanks in part to the great turbocharger resurgence. Modern production oil coolers generally fall into the air-to-oil variety or water-to-oil tube type coolers that live inside radiators.
Mustang turbo from Mishimoto shows off its coolers under the skin.
After its first great wave of turbo boosting from the late Seventies and into the Eighties, the factory turbocharger has returned to extract big power out of small displacement engines. Oil temperature control is back into the engine survival playbook. Cold start protection comes by way temperature bypass valves with thermostat control but red hot turbocharger housings can put enormous demands on motor oil. A larger capacity oil cooler can mean the difference between ongoing turbocharged motoring entertainment and a connecting rod poking through the side of the block after some unwelcome rod knock.
Factory issue oil cooler survivor from the first great wave of production turbocharging in a tight spot perfect for an auxiliary fan assist oil cooler upgrade.
Excess heat is not only the enemy of motor oil and engine parts but is also a known killer of transmissions. Sending more power through a transmission can overtax the gnashing gears, cogs and clutches inside the transmission case. Towing is another source of transmission stress and factory-issue tow packages include a larger capacity oil cooler as part of the deal. Automatic transmission fluid is oil of a different stripe. Even something as simple as a larger diameter wheel and tire combo are four good reasons to step up with a larger capacity transmission oil cooler.
Transmission coolers with auxiliary fans are ideal for tight locations with restricted airflow.
Differentials in Line
Sending more power down to the ground can create destructive heat inside differentials. Peer into a Sixties-vintage hemi-powered NASCAR super speedway car and there will likely be a massive oil cooler dedicated to the preservation of ring, pinion and rear axle for hours of punishment at 200-plus miles per hour. In modern times excess heat can also trigger modern built-in electronic safety measures. Development testing of the in-house Mishmoto Ford Focus RS saw heat buildup in the rear differential cause the computer to back down on output and rear wheel vectoring. Keeping the rear end gear oil cool not only helps the differential live but can help you live it up.
Heat is the enemy of differential gear oil in the from '60s-vintage stock cars to the rear differential in the AWD Mishimoto Ford Focus RS.
Power Steering Overheat
Race level driving can wreck havoc OEM power steering systems and easily outrun factory power steering parameters. Inside the power steering system? You guessed it - oil. Sometimes even ATF. The factory power steering system might be fine for interstate jaunts or one-finger fancy parking, but throw in drift day clutch dumping and high RPM autocross action and the smoke show from power steering overflow hitting the exhaust manifold won't be pretty. A power steering oil cooler upgrade adds capability and is a lot less expensive than replacing a pump and steering rack full of disintegrated pump bits.
Universal power steering cooler kits can help power steering systems survive high RPM race punishment.
Choice is Good: Stealth or Style
Stock oil coolers can get the job done but cost is often in competition with capability in the complex world of automotive manufacturing. Besides. Cranking up boost, towing, amped out driving behavior and/or race use can outpace even the best factory engineering. The good news is performance-minded folks like the crews at Mishimoto and B&M are hard at work figuring out what works and what doesn't. Everything from application specific factory fit with stealth black finish to race-inspired Shakotan-style external front mount hoses-gone-wild upgrades are out there. Make your choice. Keep your cool.
Photography courtesy of B&M, Mishimoto, and the RXSpeed staff.