I'd always been told to avoid chemiweld if at all possible due to it blocking your radiator... I have used 'irontight' though on a few motors and had much success! You put a lot less irontight into the radiator vs chemiweld, so there's no way it can really block up.

We ran a L20B on gas for 3 years with a crook head on irontight. Just gave it a dose once a year, and when we finally pulled it apart, the head was actually very bad, but the iron tight had sealed it up ok. Also kept a corolla and a 4 cylinder BMW going with the stuff for up to 12 months after they had been boiled badly.