Okay so this is my first time being on a forum so bear with me if I do something wrong. About 2 months ago I picked up a 2004 g35 sedan, the guy drove the car to us and we test drove it with no issues. Checked for leaks and flaws and saw nothing.
the minute we got this car on the parkway it started to overheat. I needed to drive it half an hour home so I poured out the reservoir and kept going, with the temp balancing out.
eventually, the reservoir filled back up to the top and would overheat and boil. This process happened a few times. Where I would either empty a little fluid out, bleed the car, or just let it sit.
Finally after changing the thermostat and bleeding AGAIN, no change. Took it to my mechanic. He said he just bled it but it was a nightmare and took him an hour. But after he drove it for 25 minutes, no issues. I got the car. Drove it for about 45 minutes to an hour... overheat but not much just a tad over normal temp
driving home from work today it finally overheat all the way back up to the top line. I have no idea how it could be getting air in the system, but if anyone has any idea what could possibly be the problem, please let me know. I'm dying over this.

My mechanic letting me know shes good

45 minutes after mechanic

Overheat after driving from work [auxiliary mode dont mind the other lights]

 

These cars can be very temperamental to bleed air out of, consider asking your mechanic if he used a no-spill funnel and bled air out of the rear bleed point near the firewall by the battery. It’s a very difficult car to bleed correctly.

 

+1 to previous response, over the years I have replaced my coolant I have experienced the temperamental nature of getting all of the air out of the system. Based on personal experience, it is possible that you may have a small leak some place that isn't evident and is letting air into the system. Not sure if or when your coolant hoses have been replaced.

 

I am almost certain he did, and I also have myself a few times. Somehow air is remaking it's way in after the bleed with no sign of what's causing it. I've noticed a tiny amount of radiator fluid in the fan shroud once before but nothing that stood out like a massive leak to me.

 

Have you followed the trouble shooting steps in the FSM?

https://www.nicoclub.com/service-man...F2004%2Fco.pdf

See page CO-6

A pressure test may help you?

Good luck

 

I have done a majority of these things to no avail.

Also an update, last night the car got hot again. It seems my radiator hoses sometimes have liquid [or pressure] in them and other times don't. Like sometimes they're easier to squeeze than others. But here is my radiator reservoir overfilling last night after the overheat

 

What were the results of the pressure test?
Are you using the correct radiator cap?

What happens when you start your vehicle when cold with the radiator cap removed and the engine warms up?
Does any air bubble out?
Are the fans running?
Did you test the thermostat?
Does your vehicle still have the original water pump?

 

Still waiting on money for a pressure test,
brand new radiator cap, and thermostat. It does have the original water pump, however I'm not sure if the pump was replaced with the engine when the engine was swapped, previous owner swapped the engine at about 175k miles with a newer vq35de and it seems the fans turn on immediately when the car turns on but I'm not sure if they stay on while driving or not

 

Did your mechanic check for a blown head gasket?

You may have air in the system and you keep pouring coolant out and drawing more air in when it cools.

I'd suggest getting a new oem rad cap (my friend put your style on a 04 Maxima and it gave him problems) and spending a few hours on a Saturday bleeding the system properly by jacking up the front of the car as high as possible, and going through some warm ups/cool downs while squeezing the upper hose like you're choking a turkey that owes you money.

If this doesn't work, your best bet is throwing in the towel and bringing it to someone with the proper equipment to find your problem.

 

What you are doing wrong is not downloading the FSM Cooling system and completely following the troubleshooting steps in a logical manner.

https://www.nicoclub.com/service-man...F2004%2Fco.pdf

Thus far you have failed to perform a required pressure test, used an OEM radiator cap, and used the proper Nissan recommended coolant so why are you surprised that you are still having a problem?
You have an almost twenty year old vehicle and almost all of the parts are at or near end of life.
If you can't afford to complete a pressure test then I suspect that you are over your head and purchased the wrong vehicle?

Good luck you

 

I would start with a pressure test as well as making sure the fans are actually spinning on high speed.

You can easily test the high speed function, start the car, turn on the AC. This will force the fans into high speed regardless of engine temp. If it doesn't go into high speed range it could be a bad relay.

Also take a flashlight and physically look at the fans, do they look like they're spinning VERY VERY fast and generating a lot of air movement/noise? Sometimes when the motors are old and weak they don't spin very fast.

 

I also had the issue with the reservoir bubbling, pushing out coolant and overheating. Turns out I had a blow head gasket. I bought a combustion tester for $40 and it confirmed it was a head gasket issue. Hope this helps.