Years ago I had a head to block leak on a Plymouth K-car. I tried a sealer, probably Bars-leak. The leak was only temporarily slowed. I eventually had to have the head gasket replaced. It was then that I discovered that the leak sealer had also plugged up the heater core. I had to have the core cleaned out.

I doubt that leak sealer will help much where the leak is between the cylinder and the coolant passages. It might be ok to try but don't expect miracles and don't use too much or you may have the heater system problem I had. Better to just repair the head gasket problem.

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1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog