Why is coolant mixing with the oil in your 2001 Hyundai Elantra?

Answer 1

At best you have a blown head gasket that is letting coolant into the cylinders and from there past the pistons into the sump where it becomes emulsified with the oil and will destroy the rest of the motor if you run it.

Or it could be a warp or a crack in the head same symptoms but a lot more expensive to fix.

And then there is the possibility of a crack in the block that's really expensive.

No mater which one it is it has to fixed before you run it again because the coolant in the oil will destroy every bearing in the motor.

It can also commonly be a ruined Intake Manifold Gasket. This is a more common problem in GM vehicles, but can also occur in others as well. This is still not a cheap fix, but less expensive than new heads or head gaskets.