I have been contemplating gushing my cooling system but I don't want the strong acid inside of the Heater Core.

So I have been looking on other sites. One guy on another site suggested cheap Vinegar white is usually %5 acid.

Harbor Freight has a hand fluid transfer pump which I have used in the past for Fuel, Water or Coolant. I figure I can use that to circulate the Vinegar through only the heater core and the Vinegar is not likely to eat up the Heater Core.
I think using the hand pump is also safer then using a garden hose. It gives circulation without a lot of pressure.

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84 300D, 82 Volvo 244Gl Diesel