You might use this "tank valve" which is less than $3 at O'reillys. screw it into the 1/8 NPT coolant temp sensor & add some psi from your air chuck & grab your tire psi gauge & pump in 5 or 10 psi. use short blips with the air chuck cuz you can reach a critical psi quick & blow out some coolant hoses real quick (it ain't like airing up a tire). it'll make the leak leak