Unfortunately buying a brand new Buick is out of the question for me at the moment. I have been doing some used car shopping and found a 2003 Century that seems great.

Like all Century's it has the 3100 V6. Can anyone give me some feedback on this motor? I have had other vehicles that have the old tried and true 3800... is the 3100 as good? I haven't been able to find a whole lot of info (good or bad) on it.

In my experience, the 3400 is better, both from a fuel mileage standpoint and longevity. If the vehicle has been maintained properly, the 3.1 is a fine motor. The Century is one of the safer used car bets, both from the standpoint of the vehicle's reputation, and for the demographics of who buys them. Contrariwise, a Z24 would be one of the WORST picks IMO, for the latter reason.

the 03 motor would be the "3.4 part enhanced" motor over pre 2000's. my 99 MC 3.1 has done fine (from 100k to 143k) in the 4+ years we've owned it, (only a few quirks my car has)

ask if the motor has had the intake gasket replaced recently, look for any oil residue in the overflow reservoir.

how many miles this century have?

The 3100 and 3800 are about equal in reliability in my eyes, the 3400's got some more issues than the other two such as head gaskets....

The 3100 had Head Gasket problems pre-1997 before the Gen III Engine came out...

Overall, anything with the 3100 Gen III or 3800 is a good bet... the Century was the most reliable Midsize Car according to JD Power for almost the entire span of the final generation between 1997-2005.

Unfortunately buying a brand new Buick is out of the question for me at the moment. I have been doing some used car shopping and found a 2003 Century that seems great.

Like all Century's it has the 3100 V6. Can anyone give me some feedback on this motor? I have had other vehicles that have the old tried and true 3800... is the 3100 as good? I haven't been able to find a whole lot of info (good or bad) on it.

Check out some Chevrolet Corsica and Beretta sites, that was the V6 that those cars used, and they were used for many years. I've never heard of a major issue with them.