Daughter got in a fender bender with a tow-ball on the rear of a pickup. We've had the 2003 G35 sedan forever and has been a great car, hope to keep it. BUT, after trading license info with the truck driver the car started to steam and overheat so she pulled over when this happened (a few miles down the road after the accident.) I went to meet her and had her move the car off the street into a parking lot, it was leaking a bit of fluid on the way. The radiator appears to have lost no fluid, the fans are working fine. It will idle in front of the house forever, but when I take it for a little spin the temperature starts to go up a couple miles from home. The motor started to stutter with engine light on as I pulled into driveway. Steam was coming up between fan and radiator though I haven't found the leak yet. I'm guessing I've got a leak in the system (?) but why is the radiator full?

 

Sounds like she punctured the radiator and/or a coolant hose somewhere. First and foremost, you need to find the leak and repair/replace components as necessary.
These cars are notorious for getting an air pocket/bubble in the cooling system, thus causing overheating issues like you are experiencing. The radiator can appear full even if there is air present in the system, as the heater hoses run above the engine block. Thus, air bubbles will rise the to the top (heater hoses). With the engine cold, open the bleed port (passenger side rear of the engine bay) and see if there is coolant present. Be careful as the bleed ports are known to break or strip out! If no coolant is present, you will need to purge the air out of the system.

 

Thanks for the feedback Andrew. I will check this out.

 

Rent a coolant pressure tester, typically the auto parts houses just require a security deposit and don't actually charge you for the rent when you return it. Pressure test the system and look/listen for the leak.

It's super easy, about as difficult as filling a basketball with air, check out a youtube video.