[Shortbus]

The Check engine light should not have anything to do with the coolant. You will want to get that checked out.

If you have oil in the coolant then you have coolant in the oil.

Check the top of the oil filler cap and the dipstick indicator for signs of a heavy milky buildup on either of them.

You may just have a lot of rust in the radiator core.

They make a flush additive the can break a lot of the rust free from the system and clean it out, but you may need to have the core rotted out by a proffessional.

Also make sure that the recovery bottle is not fooling you. A lot of times a rust colored slime will build up on the inside walls of the coolant recovery bottle and make the coolant appear to be extrememly dirty. I assume you have the orange dexcool antifreeze.

Check those and get back to us with some more details.