I have a 2006 Kia Optima LX, 6 cylinders.
I was told to replace the timeing chain at 60,000mi by one mechanic and 90,000 by another. What is the truth?
Timing chains do not need periodic replacement.
I tried looking in the Gates catalog and was unable to find your engine listed, which makes me suspect that you do, in fact, have a timing chain. You can confirm this by looking in the recommended maintenance schedule that came with your owners’ manual. If you have no reference to a replacement, than you have a chain and do not need to have it serviced. If the maintenance schedule does list a timing belt replacement interval, than you have a belt and the replacement should be done in accordance with that schedule.
You need to tell us the answer to two questions:
Does the car have a timing chain or a timing belt?
What does the Owner’s Manual have to say on the topic?
It is more likely that the car has a timing belt, rather than a timing chain, but simply looking at the maintenance schedule (probably contained inside the Owner’s Manual) will give you the information that you need. If it has a belt, the maintenance schedule will list the interval (in terms of both odometer mileage and elapsed time) for changing it.
If it has a timing chain, there will be no change interval listed, as timing chains normally last for the life of the engine, or are good for at least 175k miles, as long as the owner changes the oil often enough and avoids a lot of full-throttle acceleration runs.
The truth lies inside your Owner’s Manual.