1996 Oldsmobile Cutlass Cutlass Ciera Overheating

First of all, I am not a certified mechanic but I have always repaired my own cars for the past 23 yrs. I have the same car as you. GM 3.1 V6 enigines are known for developing leaks at the intake gasket. Your heat likley does not work because of loss of water somewhere (I think mine is going out the exhaust pipe ultimately). Check the color of your oil and the cap on your radiator. I dont have full contamination, but evidence of my problem is a yellow film on the oil cap (mixture of moisture and oil) and a black sludge on my radiator cap (also cross-contamination). If I had fulll contanimation of water into my engine, the oil itself would become a milky yellow color. That's bad because water into the oil can cause main bearing failure and other problems. On some online boards I have seen people mention loss of water around that gasket to the outside area or their engine. Is this the origin of the steam you see behind your engine. Hot water from the engine finding an exhaust pipe or something? A less likely scenario is that you have a head gasket failure or crack in the head or block. I hope this helps you or someone else diagnose your problem.

OK, sounds interesting; how hard is it to replace the intake manifold gasket? My oil is a milky yellow color. Why is it unlikely that it is a crack in my block or a blown head (of course I am glad to hear that it is unlikely)?

I should rather say that it is not impossible that you have a head gasket problem or crack somewhere in the head or block. However, the intake gasket is such a common issue with the 3.1 and 3.4 issues it is far more likely to be the intake gasket problem. These engine are pretty hardy with the exception of this gasket issue. Don't drive your car much, if at all, with the oil contaminated. Get the repair done first and then do a complete oil & filter change.

I am sure there are many links of interest for this issue.