my 2003 jeep liberty sport 3.7/5 speed check engine light gave a P1281 code(not in Haynes manual) apparently its a manufactures code for a coolant problem. says that engine not reaching proper operating temp usually due to thermostat sticking open constantly letting coolant flow. there for cat converter not getting hot enough making it run rich and get poor mpg. New thermostat has less than 500 miles on it since engine has been completely, professionally rebuilt from top to bottom and water pump was done. temp gauge shows half and if I leave it running for a few mins cooling fan kicks on do these two things mean the engine is reaching operating temp? and this could be something different? Im about to change oil and flush radiatior after break in period of 500 miles should I just change thermostat and see if light goes off? engine runs fine except the check engine light and mpg I just did all 4 o2 sensors per prior check engine light (it went off and mpg got better) then light came back on and gave this code.