Hi. I own a 2004 Nissan 350z that overheats when going uphil in a hot day. After cleaning the radiator, flushing the system, and making sure no air pockets remained in the heater line, the car still overheats in the aforementioned conditions. The water flows out when the radiator cap is off and the engine running. I ran a radiator pressure test and it held about 30Psi. Then ran a compression test which gave 200Psi for all cilinders. All this to make sure the head gaskets are ok. What could be the problem here?

 

Even though the radiators full put some coolant in the reservoir that fixed my problem.

Also could be thermostat or water pump.

 

9 out of 10 times it's air in the system. They are crazy tough to bleed.

 

This is also very likely. I bled mine for awhile even though I never touched anything for awhile there and the bleeding and putting water in the reservoir did the trick.

 

Not sure how these cars work dealer flushed my Z never had a problem. But I had a older work truck over heat on me ended up being the thermostat was stuck and this was after I flushed it. Good luck

 

Drive the car until it starts to get hot then feel the lower radiator hose. If it's noticeably cooler than the upper hose, you need a T-stat. Common for them to fail closed on a VQ35.

 

this is smart...

I had heating issues a little while back and I removed my thermostat element to cycle coolant 100% and also bled/vacuumed out air (in a mad scientist sort of way) before my issues cleared up.