How much oil in the oil cooler please?

[RedClive]

My next task is to spray the front of the engine with engine paint. 


I recently changed oil and filter.  Does anyone know, if I take off the oil cooler to clean and spray around it, how much oil I will lose?  Will I need to drain it first or will it just be what's in the cooler, in which case I can top up afterwards?


Thanks.