Good evening.
First of all, additives for head gaskets rarely work. They complicate things by clogging the radiator and heater core. The proper repair is to replace the head gaskets.
As far as the procedure. You need to drain the block of all coolant. Then add water. Then add your sealer. Let the engine run until it gets to normal operating temperature. Then drain all the water out and fill with coolant.
If you add it to the coolant, it will nothing. The coolant cancels it out.
Yes, the oil/filter needs to be changed to get the coolant out of the oil. If you do not change it, you will damage the main and rod bearings.
Roy
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Saturday, September 22nd, 2018 AT 3:51 PM