Two problems related to timing tensioner have been reported for the 2008 Hyundai Sonata. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Hyundai Sonata based on all problems reported for the 2008 Sonata.
When vehicle is started from a cold start, there is a noticeable rattle coming from engine that lasts about 3-7 seconds. Also while accelerating, the rattle is persistent with throttle input. I was told that the problem is the timing chain tensioner and that the Hyundai Sonatas have defective timing chain tensioners. I went to the Hyundai dealership and they quoted me $1,100 to fix the problem and made me aware that there was a TSB but not a recall on the part even though there is a revised tensioner. This is a ongoing issue and a hazard because the chain could have to much slack and cause the the timing to be off and future damage for the engine.
On startup when cold, engine makes knocking or tapping noise. Noise goes away after +/- 30 seconds. I'm told it's a timing chain tensioner, a known problem in these 3. 3 v-6 engines, but Hyundai will not recall them. The reason, I'm told, is that the engine must almost be completely removed from the car for repair.