The block of the engine may be aluminium, but there are hundreds of parts in the engine that aren't. Not to say that the sentry is actually effective or worth anything, but an 'aluminium' engine is anything but.
That goes with the magnets to purfiy water, give you better gas milage on you gas line and better health if you wear them.
I think my refg is Colder because we have magnets on it.
Save your money and change your oil......