stock thermostat
The stock stat is actually stamped as "86C" on the unit, which would be a 186*F temp. GM claims it begins to open between 177-184*F. It is fully open by 190-195. The Hypertech 180 maintains the same running temps as a stock unit (I have tested this), so don't waste your money buying that one. It's called a "180" but that is only the temp it begins to open at, it's not fully open till 190+. No matter how cool the weather was at steady low rpm cruise, or how low I set the fans, neither the Hypertech 180 or the stock 186 unit ever let my running temps drop below 190-192.
These days I just use a stock stat and set the fans to maintain a cycling range of 194-204. That temp range has given me the best overall results on a stock to medium modded LS1. If you are running much higher compression, boost, or a lot of extra timing, you might want to run cooler.





