oil in water
Get new motor
May just be blowed head gasket,but like poster said above,once water is on crank the motor probably not worth it,unless you do a total rebiuld top to bottom.
If it just started Change the oil & filter, drain the radiator and block of coolant and turn over engine but don't start it to coat the internals with oil while you wait until you have time to open the motor for look/see that way if its a head gasket it can be saved.
This isn't an answer. Still more of the question really. We already drained the block, left the oil drain plug out and for the heck of it put a hose in the radiator and it came straight out the oil pan like a faucet. More problem than a head gasket right?
The last intake gasket I replaced let entire radiator drain into the crankcase.
I would fill it back up with oil unless your sure it ran for a while like days & months with milky oil.
The internal are milled metal and rust exposed to coolant and air.
Leave the radiator empty for now so. Cheapest oil is fine. Engine may be gone but may not as well.
Never the less there is a major problem. For coolant to flow threw into the oil pan that fast is not good. More than likely a cracked or extremely warped head from over heating. enginecreator is telling you what to do to determine the extent of the damage done to the crankshaft, and camshaft bearings. Your not going to get away with an easy fix. The motor should come out and torn apart and inspected, more than likely rebuilt or replaced.
If it is a V-6, check the lower intake gaskets.
Intake gaskets or head gaskets. Likely intake, unless you ran it hot. Then see first answer, get a new or rebuilt engine.
Looking for a Used Mustang in your area?
CarGurus has 41,065 nationwide Mustang listings starting at $900.
Search Ford Mustang Questions
Ford Mustang Experts