No thermostat. Operation is very simple...oil flows into one area of the cooler, and engine coolant flows into the other (2 holes for oil, 2 for coolant). The coolant helps warm the oil up form a cold startup, and also helps cool it once at operating temperature. I wouldn't go replacing it, unless you have verified that engine oil temps are routinely over 275*...and you can't use a scan tool to check. The Cruze uses a "calculated" engine oil temp. You'll have to use a temp probe in the oil pan, to get real numbers.