Impala 3.4L

• Automatic transmission
• 50,000 miles

This is the latest of many problems with this car. It is no wonder that GM is dead. I only wish that I was not paying twice - once to fix this heap and once to delay GM's well-deserved demise.
The dealer wanted $2000 for the repair. I found a great mechanic who did it for $1400. His explanation of the cause makes sense. But it sure makes no sense to build an engine like this.
The engine block is made of cast iron. The cylinder heads are made of aluminum. The two different metals are bolted together with the head gasket in between. If the engine ever gets hot, the difference in the expansion of the two metals destroys the gasket. From high school physics, I remember that this has to do with the coefficient of thermal expansion. I looked up the values for iron and aluminum. If turns out that aluminum expands twice as fast as iron as the temperature rises. Did the GM engineers think about this? Even if it is not a problem at normal engine operating temperatures, they need to consider the very real possibility that the engine will overheat at some time and make sure that this does not cause such a major failure. I do not recall any overheating, except of course once the head gasket had already blown.