So i was driving to work on the turnpike about 75mph and i look down and my temp gauge is spiked maxed out on hot. so I pulled over immediately and let the car cool off and I looked at it some. I am not the most knowledgeable with it comes to diagnosing the issues with cars so id like some help. The radiator fans are fine they both turn on, the coolant is still full but there is no pressure in the hoses going from the radiator to the engine while it's hot and on. I don't think it's an issue but possibly worth mentioning there is a small hole in the reservoir on the top of it.

 

I'd check your thermostat first and see if it works correctly. You'll have to drain some coolant out and then stick it in boiling water to see if it opens or closes.

After that check the other components and rent an engine block tester for like 20 bucks. You take some coolant out of the radiator top, start the car, and suck in air through the tester. If the fluid changes color inside it means your head gasket is messed up.

 

I checked the thermostat and it didn't open and close when i boiled it so i swapped that one out with a new one im still having the same problem, Also the heater doesn't work it only blows out cold air.

 

Take your sedan to a radiator shop in your area, have them pressure test the system. They can evaluate the flow of the fluid and discover what is causing your overheating issues. Might be as easy as a new radiator cap if your is losing pressure or clogged up radiator radiator shop can tell!
Gary

 

I'm always amazed that no one ever bothers to read the overheating troubleshooting in the FSM.

http://www.nicoclub.com/service-manu...6_G35_Sedan/co

See page CO-6

With a almost 12 year old vehicle the coolant, thermostat, radiator cap, and possibly the water pump,hoses and belts should all be replaced.

Do a pressure test and remove air from the cooling system.

Just my $.02

Telcoman

 

I'd try bleeding the system out of air, since you opened the system. The cold air in the cabin is a sign of air in the system, but doesn't mean the overheat didn't do anything.

Rent a pressure tester from the auto store. You can then test your cap and system. You could probably just replace the cap anyway, since it's old.

Are both the radiator hoses hot when you touch them.

 

I had the same issue, there was a small crack in the plastic in the top or radiator where it meets the metal, it was gradual problem until it split open and leaked everywhere. I had a new radiator and thermostat put in at the same time. Thermostat is cheaper than a radiator. maybe only $70 to do, IIRC.

Local shop charged $500 including parts for radiator and thermostat replacement. I felt it was worth it to go ahead and do both, I was in a hurry to get my car so that worked out the best from a time/cost perspective.