bump... I hate to bump an old thread but was this ever figured out by anyone? My problem arose when i was doing an engine sway. I bought the Mishimoto radiator and thermostat that opens at 62C. I have been reading that the thermostat is opening sooner than the ECU says the car is at normal operating temps, but i doubt mishimoto would sell it without expressing that problem.

I keep getting the code and getting it cleared. The car is staying well within normal temps. Most of the time, way under because its been so cold lately. Other symptoms i am having are with my heater. I think there is air in the system.. but cannot seem to get it tracked down. I have been driving the car daily and everytime i open the radiator, the neck is full.

Thanks

 

That thermostat is way to cold, 62 deg. C = 143 deg. F The factory thermostat in the 350 Z is set at 180 deg F. Your engine will be too cold to operate efficiently and is taking too much time to get to operating temperature which is why you are getting a code.

 

I just got P0128 3700 miles after my stroker. Mishimoto Radiator,T-Stat, & Forged fan shroud & fans went in.

I was on the freeway at 3k rpm, it was 6am and 5x degrees. Coolant was at 165 degrees and the car was running fine.

Should I be concerned?