Part 1 : Let's talk about the standard Subaru oil cooler .

The main functions of factory oil coolers in turbocharged Subaru models include:

1. Temperature Regulation: Factory oil coolers help maintain stable oil temperatures, ensuring that the oil does not overheat during demanding driving conditions, such as racing or driving in hot weather.

wrx 2.5 standard oil cooler shown below 

2. Enhanced Lubrication: By keeping the oil at optimal temperatures, the cooler ensures effective lubrication of engine components, including the turbocharger, which is vital for performance and longevity.

3. Rapid Heating of Oil: The factory cooler also assists in bringing the engine oil up to its optimal operating temperature more quickly, which is important for engine efficiency and reduced wear during cold starts.

4. Integration with Coolant System: The factory oil cooler functions as a heat exchanger, utilizing engine coolant to help control oil temperatures, thereby enhancing the overall cooling system's efficacy.

5. Improved Reliability: By preventing overheating and ensuring proper lubrication, the factory oil cooler contributes significantly to the reliability and durability of the engine under various driving conditions.

These functions are particularly crucial in turbocharged models, where higher power outputs and heat generation put additional stress on the engine's lubrication system.