Oil in radiator , but there is no oil and water mixing in sump

Cleaned water system, washed all pipes, cleaned water pipes, flushed radiator ,filled clean water. As soon as i started the engine and opened the radiator filled cap, oil was mixing in the radiator . Strangely there is no water mixing in in the sump .

What model could be intake gasket broken

I am assuming its motor oil and not transmission fluid, right ?
You can have a leaking intake gasket or head gasket and get oil in the coolant without getting coolant in the crankcase.
Same thing opposite. The bigger the leak, the better the chance of getting both at the same time.