What is the difference between the two?How about their engines? and their MPG?
I`m talking about a 1998 Model.do they have 4.6 or 5.4 engines.l think some expeditions have a 4.6 maybe; but how about the navigator.What are the features that the navigator has better then the expedition?

l think just the inside is different, basically going for looks

they're the same thing. a navigator is just a rebadged clone of the expedition. engines are the same which means MPG will be the same. Lincoln and Ford are both branches of the Ford Motor company. The navigator and expedition will look a little different though, and the navigator will probably have more features.

here is a side by side comparison for you;
http://fordvehicles.com/suvs/expedition/compare/details/?vehicles=19378|19827|19379|19828

Did you know that they both come in an Extended version now ?

My Best guess would be the price.