When I purchased the vehicle, I was aware that it was running hot.
As a TECHNICIAN, I performed extensive diagnosis on the vehicle. The first thing I found is that the heater control valve seemed to be the culprit. After repairing that (used a h/c valve off a 94 Chevy Caprice), the system held too much pressure. After performing a compression test and cylinder leak down test, it was revealed that the head gaskets were blown/leaking. I removed the engine, and to my surprise I must say that it is a VERY uncomplicated design. The only thing that I would have done different is not submerge the engine oil cooler in engine coolant; good theory, but not practical for real world application.
The day before I pulled the engine, I noticed that the oil gauge dropped to zero while sitting at a traffic light. Upon disassembly of the engine, I noticed that the pressure relief valve was stuck.
Also on the same day, upon take off from the traffic signal, the transmission, for the first time, was very sluggish.
For all those out there who don't know, all these problems are directly related to one thing!! Many people trust their vehicles to their favorite mechanic. However, today's car require a competent, experienced, and fearless TECHNICIAN!! And folks, there is a difference!! A mechanic is anyone who is mechanically inclined. He knows how to remove and replace parts. A TECHNICIAN knows how all those parts WORK and RELATE to other parts on the vehicle.
As much as many people trust their vehicles to dealers, I am sorry to say and I am sure that most of you are embarrassed and in some cases too angry to admit, the level of expertise you expect is just not there. I won't attempt to explain this phenomenon here. You should know though, that there are in many cases only mechanics in dealerships, and sadly enough, many are ASE Certified.
I am a TECHNICIAN!! This is what sets me apart. Don't believe me, ask me anything, and you will readily see the difference. These car's are built on a German platform; enough said. The engine is all GM. While in opinion I think some things could have been designed differently, I would readily buy another one! They are very capable sedans! They are luxurious and swift! I would love to exchange comments and answer questions about your Catera. My e-mail address is apexindustries at yahoo dot com. I am more than happy to help you change the perception of your Caddy with Zig!