For a 96 Saturn SL1, is the engine all aluminum or is it an aluminum head with a cast iron block? Has anyone on the list had a head gasket fail on them at high mileages (~175,000) even though the car was never overheated, coolant/oil was kept changed? I can't figure out why the head gasket failed on this car (oil gets into the coolant... it runs just fine) but I am wondering if the cyl head is aluminum and the block cast iron, that perhaps the two different metals somehow caused the head gasket to fail after all the heating up and cooling down with many miles of normal use. I've never heard of a head gasket failing on a car unless it was overheated.