Originally Posted by kerry

No, it heats the engine as the heat rises thru the coolant from the hose and into the engine. Doesn't heat up quite as fast as the block heater but fast enough to decide not to bother trying to remove the plug on my other cars that needed a heater.

If I had the manifolds off with easy access to the plug I might think otherwise. However, the amount of effort people have described using to loosen that plug has made some people think there is the possibility of cracking the block during the removal procedure.