Engine oil does more than just lubricate the bearings. It carries heat and is a part of the cooling system as well. Added power, track days, and just driving the car hard on the street puts extra heat in the oil and rest of the cooling system. As oil heats up, the viscosity decreases, i.e. it gets thinner, which weakens the protective layer of oil between your crankshaft and bearings. Too hot, and that layer can no longer support the load and you get physical contact and damage. Also known as a spun bearing.
In our experiece, there are a few things that can be done to make a Subaru more reliable in extreme conditions like a race track- Keep oil going to the bearings, keep the temperatures in check, and keep the engine from knocking. As long as you do this, you can drive it pretty hard for a long time. An oil pan upgrade, bigger radiator, good tuning, and good fuel are all options. Gauges to monitor oil pressure, oil temperature, and coolant temperature allow better monitoring of engine conditions.
To truly know whether additional oil cooling (many Subarus have a small water-oil cooler above the filter) is needed, oil temperature should be monitored, but for any car that sees track use and/or makes a good amount more power than stock, it's a safe bet.
While many people build their own kits, Perrin offers a complete, ready to bolt on setup for most Subaru models. Some kits offer components of questionable quality, but Perrin has started with Setrab core and Mocal thermostatic adapter. This provides optimum cooling with a minimal pressure drop, and only passes oil through the core when temperature are above 185F (over cooling the oil is not desirable either, it needs to be in the right range). To make all this fit, they include custom-machined mounting brackets to fit specific models, pre-made oil lines with heat shilding where they pass the header, a spacer block to provide clearance past the timing covers, and even a new OEM oil filter.
When installing a Perrin oil cooler, we recommend removing the stock oil-water cooler if equipped. Otherwise there is too much stuff hanging down below the block, exposing the oil filter to potential damage. This can be done by simply routing the line exiting the bottom of the block to the crossover tube that returns to the oil pump. Optionally you can install an 08-14 WRX water pump, which only has 2 inlet ports, and a plug for the bottom of the block.
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Manufacturer Perrin Part # PSP-OIL-099 Made in United States MSRP $745.00