Hi all! So Im preparing to do my timing belt installation for tomorrow and notice in the coolant overfill container there is oil in there and its pretty bad, luckily no milky colored oil on the dipstick or filler cap! Im guessing the oil has been in the cooling system at the most 1 month, because that was the last time I had to fill up on coolant because there has been a slow leak.

Im doing the T-belt, water pump, etc.. Im also putting in a new radiator, Im going to try that first and I believe that is where the problem lies and not in the head gasket. I want to clean this system good. What do I put in there so I can run it, drain it, fill it, run it, and drain it again until clean? I obviously don't want anything caustic that will harm any rubber or gasket material.

Thank you for your suggestions!