The engine has copper head gaskets with O-rings in the block and reciever grooves in the heads. The gaskets were .020" thick, which is not really thick enough. Forgetting to retorque the head bolts didn't help either! The gaskets were pushed out in all directions, allowing cylinder pressure to enter the cooling system. This caused the upper radiator hose to burst, making a nice mess under the hood. I thought I had blown it in two! I'm now using .040 thick gaskets and they are holding up much better.