Sigma 3.5LThe Sigma 3.5L is one of the oldest engines in Kia's repertoire, although it was only available in Hyundai models for years after its debut in 1995. It wasn't until 2003 that it started appearing in Kia branded vehicles such as the Kia Opirus, allowing the engine to enjoy some brief time in the spotlight. However, these engines stopped being manufactured beyond 2006, meaning they're unlikely to be found in any modern vehicle today. Even beyond reliability concerns, this means any official support or information about these engines will be difficult for used car buyers to find.The 3.5-liter variant is especially noteworthy. Those who owned Kia vehicles with this engine had mixed opinions on it. While some have found that it was subject to failures, others have reported driving models such as a 2004 Kia Amanti up to 200,000 miles, which is a testament to its ability to hold up over time. Of course, pretty much every car with this engine will be around two decades old, so there might be greater issues to worry about than the engine itself.