My 05 G35 while driving on the highway lost power and noticed the temperature guage showed car was hot. Towed it home, started the next day and it sounds normal, no noise what so ever. it idles fine but once I try to drive it, it starts to overheat. I changed the thermostat and it still overheats when you start to drive it. No heat coming out. Friend said might be air in cooling system, we opened the bleeder screw and made sure we it over flow whIle filling the radiator but still same issue. I noticed just one fan keeps running so I unplugged both and plug it back on. I started it and both came on but the same one quickly went off again (drivers idea fan). I don't know what to do with the problem, please help!
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Common failing parts of the cooling system are the radiator, radiator cap, thermostat and the fans. Air in the system is also a big issue but shouldn't be unless you have recently emptied the coolant from the system and then put it back in. Even though your car has low miles any of these could have failed or be failing.

Before you replaced the thermostat did you pull it out and test it? If not what was your reasoning in replacing it? When you replaced did you drain the cooling system? The G is notorious for being very difficult to bleed correctly and I suspect that's your issue with the no heat in the cabin issue. When the car is warmed up do either of your radiator hoses (upper and lower) stay cool to the touch? If your radiator is failing you will probably see signs of leakage somewhere in the engine bay, a pressure test can confirm whether or not it has a leak. Fans are tougher to diagnose, the fans and motors can fail independently and on a 14 year old car this might be an issue even though you have low miles. There's a ton of info about these issues on here so hit up the search button or Google to find out more. I replaced my radiator, cap and fan assembly between 120-130K miles because they just wear out over time. YouTube is also a good resource for DIY videos, be specific with your searches if you head over there to check it out.

 

I realized it wasn't the thermostat but i had already installed the new one. I never empty the coolant but what i know is only 1 fan comes on and thats the passenger side fan with AC/heat on. there's no leak and engine sounds just normal but overheats ones i start to drive. Before it was blowing cold air but after i got use a funnel on the radiator to purge the water out, the heat works as it should but still overheating.

 

Does the other fan never turn on even once it begins to overheat?

 

Why are you not following the cooling system troubleshooting steps as outlined in the FSM?

http://www.nicoclub.com/service-manu...5_G35_Sedan/co

See page CO-6

Did you use a proper OEM thermostat?
Did you pressure test your cooling system?
Have you replaced the radiator cap?
How often has the coolant been replaced/flushed on your thirteen year old vehicle?
Possible defective water pump?

Telcoman

 

FOR SOME REASON, i called a shop to drop it off and they told me they cant see the Car until 2days due to being busy. So as far as me being mad, i went outside and started the car and watch it run for 10mins...didnt see any overheating so took it on the highway with the heater fully blasting holding my breath. To my surprise, It stopped overheating. I believe it was the air in the coolant and after purging it out about 10x it started working again. thanks yall for all the help.