1995 Buick Riviera with the 3.3L supercharger Where is thermostat located?

The thermostat on a 1995 Buick Riviera with the 3.8L supercharged engine (it's a 3.8L, not a 3.3L) is located on the engine, at the lower passenger side of the intake manifold. It's usually in a housing that's relatively easy to access once you've opened the hood. You'll likely see a couple of hoses connected to this housing; one going to the radiator and one to the engine. The thermostat itself is inside that housing.

However, accessing it might require removing some components depending on your comfort level. It's a job best done with the engine cool, and you may need tools like a socket wrench and possibly pliers. A repair manual specific to your year and model will be very helpful for detailed instructions and diagrams.

Important Note: While I've given you a general location, always consult a repair manual specific to your 1995 Buick Riviera 3.8L supercharged engine. The exact location might vary slightly depending on specific engine configuration or any aftermarket modifications.