My anti-freeze kept going down . I added about 4 liters in 30 k. The dealer said the head gasket MAY BE the problem.There was no external leaks anywhere. They preasure tested the system. They sent the heads out and had them checked. OK. Head gaskets OK Dealer replaced everything and charged me $2690.00 and said they MAY have solved the problem. So far the coolant level is staying the same but I can still smell anti-freeze. My extended warranty was about 2000 over the limit of course. I am not happy!!!!!!!

My Truck is still relatively new and my warranty just ran just before the engine begin knocking, I�ve heard from many people say that this is a common problem with the Silverado class and it�s not a major concern. But the more research that I do the more that I worry that this is not a small concern or just the Octane level of the fuel that I use. Knocking (also called detonation or spark knock, or pinging) in a spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front