Hi. first time poster here. I tried to do a search for thermostat, operating temp, engine not warming up but those searches didnt result to anything helpful.

About a week ago I started my car and immediately noticed the SES light (and no did not just fill up my gas) and ever since then my car does not get to full operating temperature unless I'm at a stop. But the moment I start going on the highway or driving, the temperature drops again. Do I need to replace my thermostat? Or is there something else that would cause the light and my car not to fully warm up?

thx

 

That sounds weird. I can't imagine how the engine temps would drop when you start running it, as the temps obviously rise when you start climbing the rpm's. It has to be a faulty sensor.

 

Well, one of a couple things are happening. Either your thermostat is stuck open which would cause your car to only reach operating temp at stand still while running or in stop and go traffic. On the highway, the movement of air across your radiator, along with the circulation of your coolant while your thermostat is stuck open would cause a a greatly reduced operating temp of about 110-120 degrees. If this reduced temp is monitored for a certain length of time by your car's ecu then your service engine soon light will appear. I forgot the specific error code but the definition is "coolant below regulated temp". More than likely this is your case. Simply change your thermostat, along with a new seal then top off coolant. Also, for some reason most auto part stores dont seem to have thermostat for our cars. My suggestion for the best bang for the buck would be a mishimoto which is about $65 on ebay. Its a new product and is half the price of the Nismo version.
Good Luck!
-M