i am going to begin a blown head gasket repair on my 89 toyota supra turbo. i know i'm suppose to drain the radiator coolant first, but am i suppose to drain the engine oil too? i konw that after i'm done, im suppose to put new engine coolant and new engine oil because they may have mixed due to the blown head gasket. are these the only things that need to be drained? thanks for listening and for any replies.

You answered your own question so what do you want me to say? :p Defintely drain everything except the A/C lines, get everything you can out of the way and it will be much easier to work on. Don't skip on the small stuff either, do all the tune-up work like plugs, wires, filters, ect. while your fixing the BHG now and you can keep track of it easier in the future.