Oil cooler

I have a 2005 dodge sprinter 3500 how do you test an oil cooler for leaks? Notice oil in the radiator gonna flush out tomorrow, but not sure how to check out the oil cooler

Flush it out and if it comes back then its your oil cooler

It is behind and below the oil filter,disconnect the coolant hose, remove 4 bolts, be carefull of the gasket, remove and clean, blow with mouth into the coolant pipe while covering the other coolant outlet on other side if pressure escapes its leaking
murray