The Stock Thermostat runs at 195 degrees.  My new replacement unit is set to 178 degrees. Current logic is that a colder engine will produce more Horsepower.  Well, that's not exactly how thermostats work, but it's worth a try anyway.

The installation is pretty straight forward - two 10 mm bolts hold the factory housing in place. The gasket is part of the housing. The only problem after locating the radiator drain plug, is draining the Dex-Cool out of the radiator (the drain plug is on the passenger side on the bottom of the engine side of the radiator).

If the car cannot be raised, the low clearance of the C5 makes it almost impossible to get anything underneath to drain the coolant into. I found a plastic tank gizmo at the local auto parts store that fits under the car nicely - it is from Wedco, holds 12 liters (12.5 quarts), has a funnel thingie on top and costs only nine bucks. Or you can use a shallow pan and drain enough fluid out to fill the pan and then empty it into another container. See Radiator Draining instructions below.

When no more fluid comes out, close the drain cock and install the new housing/thermostat combination. All you need to do is remove the hose (sometimes wrestling with the clamp is a pain - get good clamp pliers); then remove the two 10 mm bolts and pull the thermostat off.  Installation is just the reverse.  Tighten the bolts to 10 N-m (that's 89 lb-in for those challenged by the metric system).  Ensure all hoses are properly connected and clamps tightened. Then filter the drained fluid or buy new fluid and pour it back into the radiator surge tank. See Radiator Filling instructions below. I recommend that you only install this thermostat on a COLD engine (hot on the fingers!).

Initial testing shows the car running about 10 degrees cooler than stock. Having the car run cooler should help considerably during future Dyno runs.

This is also a good time to install the throttle body coolant bypass kit if you have one handy.

Radiator Draining instructions (adapted from the Helms CDROM documentation):
1. Park the vehicle on a level surface
2. Follow the steps below to remove the radiator surge tank fill cap: .

Slowly rotate the cap counterclockwise

Stop and allow the hissing to stop (relieve any pressure)

After all hissing stops, continue turning counterclockwise to remove the cap.

Radiator Filling Instructions (adapted from the Helms CDROM documentation):
1. Fill the system through the surge tank opening.
2. Fill to the top of the tank
3. Start the engine
4. Idle engine for 1 minute
5. Install surge tank cap
6. Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99 C (210F)
7. Shut off the engine
8. Remove the surge tank cap as in Draining step 2 above.
9. Start the engine
10. Idle engine for 1 minute and then fill surge tank to 1/2 inch above COLD FULL mark on the radiator surge tank.
11. Install the surge tank cap
12. Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99C (210F)
13. Shut off the engine
14. Top off coolant as necessary, 1/2 inch above FULL COLD mark on the radiator surge tank
15. Rinse away any excess coolant from the engine and the compartment.