I noticed a few days ago that the engine have been running hot on the factory gauge when I'm just putting around and idling, but is perfectly fine at cruising speeds. There was never a problem during the summer or anything, it just started happening. I checked the radiator today after I got the EU working correctly and it was full, so I really don't know what exactly could be going on?

Could it be that the thermostat is sticking or something random like that, or could their be air bubbles in the system that just aren't showing themselves?

BTW, I changed the coolant last December when I did the TT install and haven't changed or messed with it since.

 

Sounds like it may an air flow issue across the radiator. Is anything blocking the radiator (I doubt) or has one, or both, of the fans died.

 

Could be the thermostat. I had my stock one fail on me...

 

Did it fail open or closed?

 

It failed closed...and pissed me off too. Same kind of issue...car run normal temps...albeit outlet temps were a litte lower then I thought they would be..now I know why...started slow..car running a little warmer at idle...at cruise fine. The one day BAMM..thermostat wasn't opening. Confirmed by stock gauge going to max hot while my water temp gauge showed low heat on the outlet pipe from the motor...Swapped thermostat...flushed in some water and Watter Wetter with some anti freeze...fine again...for another 2 months...same thing happened again..This time I just flat out removed the thermostat altogether...I have been running no thermostat for about 3 months now and am much happier...My coolant temp from the return hose shows a 15 degree drop in temps by removing the thermostat.

 

I doubt that removing the thermostat work for us folks on the east coast that need the car to warn up on cold days. Personally, I would never remove it since the engine may never reach the optimal operating temps but, if your car is running good, stick with it.

 

Well Nissan says operating temp is 195. My outlet temps are usually around 185-190. Oil temps are about the same...

 

So what would you say I should do, just go ahead and change it out with a Nismo unit?