I have recentlyt had two of my perfect running vehicles blow their engines! The first was my camaro and it had just got new tires and the oil changed. The oil was changed without my consent an PENZOIL was put into the engin with a WIX filter. These two brands are ones that i would never consider putting on my engine. Then the second incident was with my 86' K10. The motor has less than 8,000 miles since me and my dad rebuilt it. It started out in his stock car that he raced at a local track(shut down now). But the deal is that both of these vehicles were running fine until I left them somewhere. In the time that i left them unattended could some jackass add something to my gas,oil, or anywhere to make the engine blow up within 12 hours??