Be careful with these cars, They are notorious (and many of other Mitsubishi vehicles) for having big-time "top engine" troubles. Some of the more common problems are bad valve guides, which cause low compression and oil burning. They may also have warped heads and/or blown head gaskets. This is usually traceable by noticing white smoke from the tailpipe. This can be hard to detect though. Get your mechanic to give the vehicle a compression check before buying it! These cars are also notorious for shredding timing belts before the scheduled replacement interval, which, which, when it breaks, causing the valves to crash into the pistons, and all sorts of big $$ repairs to occur. Get your mechanic to inspect the timing belt. ALSO, if the engine has ever been rebuilt because of this failure, it will never be a stable, reliable engine again...avoid at all costs!
The engines most common to these malfunctions are the 3.0 liter V6 engines, but the 4 bangers can have almost as many problems. These problems also plague the Dodge and Chrysler versions built on the Mitsubishis! Mileage is not a consideration, since these failures can happen on very young engines...likewise, there are a few high-mileage ones that have never had any problems too! Considering the Eclipse is a high-performance car, used models will probably be driven hard and dogged to death, increasing the chance of these big-time engine malfunctions!