WD40 is a kerosene based penetrant and lubricant that was (is) still used widely in aviation. It has penetrating qualities that are great if used correctly and it is a water dispersant. I use it in a number of applications, freeing up "frozen engines is not one of them. If the frozen doesn't "loosen" with an application of fuel to in internals then I strip it. "Frozen" diesel engines a common place thing, castor glugging up the works mostly, a judice use of heat plus fuel usually fixing that problem. So what I am saying is don't discatd WD40 out of hand read up on what it's intended use is and use appropriately. Another product I use when it is "cheaper" or WD40 is not available is RP7.