My dad's been a lecturer for years and he's been stuck on the top grade of the pay scale for the last five. It's a difficult job, you'll always get trouble from some kids, they'll change the curriculum on you with no notice, and there's always some 'meeting' you have to go to at 9am when you've got no classes til 2pm!
Also, you need to be able to explain things to the kids in so many different ways. It's no good telling the kid 'this is this because it is'. They'll ask why it's that way, why do we do it like that, and you have to be able to explain it to them. I think you mentioned putting oil in a car as an example, yes you can tell them where it goes, and how often to put it in, but kids will want to know why the car needs oil, where the oil comes from, what's the oil made from, etc. Your job as a teacher is to be able to answer all of those questions.
Having said that, I can imagine the satisfaction from teaching them something, and them understanding it is fantastic. I've got a 5 year old son who's constantly asking questions, and I patiently explain everything to him, and it gets annoying sometimes. But when his teacher, or his grandparents come and tell me he's told them something I taught him, it makes it all worthwhile.
Shit, that's a long post... Oh well.