Once had a minivan that developed a head gasket leak. Fortunately, it leaked to the outside of the block, not internally. The leak started off very small but soon became a gusher (happened while on vacation). It would empty the radiator in about 30 minutes. A Goodyear mechanic poured in a bottle of K&N Block seal. It held from New Orleans to Atlanta at which point I drained the system and used another can of K&N. This time I followed the directions on the can to the letter. It held for 3 years, may still be holding but I traded the van in on a new car.