First, that stuff does not work. It does nothing but clog the radiator and the heater core.
There is no such thing as a head gasket repair additive. I know they make them but they never work and cause more problems.
The only correct repair is to have the head removed and repaired as needed. The fact it will not start tells me you have coolant in the cylinders and unfortunately water will not let an engine run.
Sunday, November 18th, 2018 AT 3:27 PM