1) leaking head gasket
2) a lot of short distance driving so the condensation inside the crankcase doesn't evaporate
Leaking gaskets
Usually a lower intake gasket leak only has one symptom,coolant mixed with the oil.The oil dipstick will have a white milky substance on it which looks like a milkshake.If the head gasket is blown or the head is cracked,you will normally have numerous symptoms rather than just one like an intake gasket shows.Wet spark plugs,overheating,coolant mixed in oil,coolant level continuously drops,white steamy smoke from tailpipe,after removing radiator cap with engine running coolant will rise and fall constantly inside radiator as you watch it doing so.These are all blown head gasket symptoms but not all have to be occurring.More than one symptom usually appears though rather than only one symptom.Driving a vehicle with a internal coolant leak for too long will damage the engine.Antifreeze and engine bearings don't get along with each other.Coolant will eat the main,rod,and cam bearing surface material right off the bearing within 500-1000 miles,so take care of the leak pronto
A cracked block.
Intake manifold or plastic plenum cracked / gaskets.
A head gasket would leak oil into the coolant.
Coolant pressure is at 15 psi, oil is at 30-50 psi.
