oil coolers

[aucky]

hi guys got a couple questions about oil coolers.i no you use a thermostatic sandwich plate so the cooler only cools oil when it gets up to temp,the things am not sure about is

1 do you need to fill cooler with oil or just do engine oil as normal.

2 if you dont have to fill with oil then when oil starts going into cooler wont your oil drop bellow empty mark and damage engine,starve engine of oil,also will it effect oil pressure and will that run risk damage.

thinking off adding one to list mods for my car,thanks guys.