Hey guys, I just recently got my first G35 the other day and have been battling the cooling system since day one. First off, it's a 2004 G35X and it does not have a blown head gasket. I went and had it checked out right away. Anyways, I'm losing coolant and I havent noticed any leaks. I'll top it off, go for a 5 minute drive and the reservoir will have drained about 50%. I have driven further and it will just keep draining. I have changed the thermostat and pressure tested it. It seems to hold at about 12-13psi. I have burped the radiator multiple times with a spill free funnel and the bubbles never stop. I've ran it for over an hour and they just won't stop. I tested the thermostat in boiling water before install and it worked just fine. However, the only time I've noticed the thermostat open up is when I remove the radiator fan relay and let it idle for a few minutes. Not sure if that's normal? I've ran it for hours with the fan on and the lower hose is always cold. My coolant levels have also dropped over night while the car is off. Never all the way when it's off though. Sorry for the ranting but I just want to paint a detailed picture for you guys. Any suggestions you guys could give would be extremely helpful. Thanks!

 

Update:

I topped off the reservoir last night when the engine was cold, I took a look this morning and it hadn't gone down at all. So the coolant isn't leaking, it's burning?

 

The lower hose being cold generally means a bad thermostat or air in the system.

 

Just to verify the problem, you are NOT overheating at all but you are LOSING coolant correct?

You probably have a leak and it's escaping as steam or dripping on something hot and turning into steam and thus isn't dripping from under the vehicle, pressure test the radiator CAP first because that's the most likely culprit. If the cap passes then pressure test the entire system, be warned though you might end up causing a small leak to rupture so be prepared to fix something like the coolant bleed valve on the heater core hose which is a notorious point of failure.

 

Correct, the car has never overheated. I have done a pressure test on the radiator already, the cap itself looks fine. The gasket isn't torn and is still pretty soft, the spring is okay too. I might just get a new cap to be safe?

 

I figured it out! It ended up needing a low temp thermostat and a new radiator cap. Now the coolant levels are steady again.

 

Good deal. I'd say the thermostat was the issue. Not necessarily it being low temp, but it being the t-stat. Rad cap is a wear item IMO. When they start to fail they fail quick. It's an easy $5 part to start with.