You have either an air pocket in the cooling system or a head gasket issue, or even possibly a restriction caused by the stop leak gunk. I always try to eliminate the easiest thing, which is an air pocket but you can also get a block test kit at your local parts store which consists of a clear cylinder and a blue solution that you place over the radiator fill hole while the engine warms up, and if it turns color it will indicate combustion gases in the coolant, or in other words a head gasket issue.
Thursday, April 25th, 2019 AT 7:39 PM