Where is the thermostat housing on a 99 Chevy Malibu?

The thermostat housing on a 1999 Chevy Malibu is located at the front of the engine, on the top of the engine block. It's generally near the upper radiator hose connection point. It's a relatively easy-to-reach location once you've opened the hood. However, the exact location might vary slightly depending on the specific engine (3.1L V6 or 3.8L V6). You'll need to look closely at the upper engine area to pinpoint it. A repair manual or online diagrams for your specific engine will be very helpful in confirming the exact position.