So I have a 2009 g37x with 120,000 my car only overheats when going uphill on a freeway but then I turn heater on and temperature going back to normal daily driving is perfectly fine I have changed thermostat, cap, fluid flush, and fluid in reservoir is always normal any suggestions

 

What "overheating" symptoms are you experiencing?

Are both of your radiator/condenser fans working?

 

yes my fans are kicking on properly. And overheating as my temperature gauge goes all the way up

 

did u figure out or fix this problem