I'm working with my brother on his 1997 Caddy DeVille Concours. It has the 300 HP Northstar engine. It consumes coolant without any apparent leaks. I read that these engines blow head gaskets and the coolant is forced out of the engine. We did a compression check on the easy cylinders 2, 4, 6, 8. Cylinders 2 and 8 are approximately 120lbs. Cylinders 4 and 6 are near 100lbs. Does anyone know what the healthy pressure should be. This engine has approximately 135,000 miles on it. The car is in very good shape and we would like to repair it. Thanks.