Anyone know the best way to clean the inside of the radiator and overflow tank to get rid of the residual oil from the blown head gasket?

The radiator is best to go have it hot tanked.Same for the overflow.

Any of the detergent-based cooling system cleaners should work.

the older subaru section loves to use DAWN dishwashing liquid.

 

 

nipper

FYI, I used Prestone Radiator Super Cleaner not too long ago, and man that stuff makes the coolant foam like it's a washing machine.

 

I built my own cooline system flusher with a 3/4hp pump from Harbor Freight, some PCV piping and valves, and hose, and flushed about 10 gallons distilled water through a couple times, and it was foamy like washing machine discharge. [remove thermostat, reinstall housing incl/ gasket, pump into water pump intake, collect discharge at radiator outlet] -Louis