how can i tell if my motor is my original motor in a dodge caravan??

If you mean you recently had a rebuilt engine installed, it will be clean and shiny, no oil dripping etc. If you mean a used engine, might not be so clean but still should be able to tell. Yet another scenario is if you mean it was 'supposed to have been replaced' but before you bought the car and not recently that gets in to sticky situation. Not being able to look at the car makes it even more difficult. What was-is the problem?

Whats the problem you have