Well for starters you only get a 90 day warranty on a used (Abused) engine. The next thing is you don't know how the last person treated that engine! Did they take care of it or just drive the crap out of it? The next thing to consider is that a used engine is just THAT >>> USED! It does have some worn parts in it too. Now granted it may not have the same worn parts as yours, but it still may require some TLC in the very near future too. Basically you have to add up all the costs & compare: Price of new & used. Price to fix up used to make worthwhile. Warranty length.