Fred, it was an acute loss of coolant. My wife was on the highway doing about 70 per and a seal in the water pump let go. She didn't pick it up in time and the engine got real hot, aluminum head lifted and !voila!, head gasket went. Hope you dont get to live thru one of those experiences. BTW, Mike, there is no filter element that will get you a 20 hp increase. At least not on this planet..
1987 BMW 325