2007 g35x sedan 135k miles. It is currently hot here in IL (88 degrees) and it’s starts to over heat at idle with the A/c on. So I did a coolant flush and thermostat, on the day I did that it was low 70’s. I bled the system and went for a very spirited drive, got home and let it idle for 20 mins with a/c full blast, the car temp read abt 206.40 with the hood closed and 203 with it open. It seemed completely fine. It is now hot again and it’s doing the same thing, slowly creeping up(I usually end up shutting the car off at 221) so I’m kinda stumped on this one. Both fans are working(albeit they are the original fans and this is a Chicago car with no belly
pan) So I’ve ordered new fans, after I ordered the fans I noticed the fans seem like they aren’t sealing perfect(noticed a 0.5 cm gap on the inner side of ds fan “shroud”) it also seems like they’re isn’t two speeds for the fans, but idk if there is supposed to be. I’m completely stumped, fans are working, new t-stat, new temp sensor, coolant flush, blew out radiator, new radiator cap, made sure radiator isn’t clogged and it’s still doing this…
im down to 3(ish) ideas
1.)the fans have weakened with age and no longer blow as hard
2.) the dc sports ram air intakes are sucking in hot air making the crappy fans work harder and harder
3.)water pump is COMPLETELY toast, can’t be “starting to go out” Bc no coolant leak from the weep hole and it doesn’t created much if any turbulence
If I’m blantantly missing something please tell me I just don’t think it’s anything major(headgasket) because literally nothing point to it being one

 

I'm guessing the fan motors themselves are failing, pretty common on the V35 chassis so I'm guessing it's likely common on your V36 chassis.

The V36 uses a different high/low fan speed system, it has a fan control module to scale the speed linear instead of just high or low speed like the V35 chassis had.

You should also pressure test your coolant system just to verify it's actually holding pressure correctly, I don't suspect this will be your issue, it's also highly unlikely your water pump is the issue.

When you turn your AC on it should always switch the engine fan speed to high. Test this with a cold engine like when you first start it for the day, let it run 10 seconds then turn the AC on and the fans should kick on to high speed.

 

I put the new fans in, they seem to blow a bit harder, but it hasn’t been scorching hot yet so tough to tell if it fixed it, the weird thing is, if I beat the hell out of it(6 0-60 back to 0 ) the temp will get up to 222, and then I can stop and it will cool itself down to 203 and sit there as idle, where as if I just drive around and come back and sit, it will slowly creep up to 212 and sit there(idle, a/c full blast, 84 degrees outside) idk why, it seems like 220 engages the fans to max and it wants to get all the way down to 199 or something…
mans as for the pressure test, I haven’t ran one but the hoses are still hard after abt 3 hrs, so I think it’s holding pressure fine.

 

It's actually really hard to tell the difference between 8psi of coolant pressure vs the normal 12-13psi of coolant pressure. I would still pressure test it since you can usually just "rent" the pressure tester for free (security deposit is usually all the parts houses need and it's refunded when you return the tester).

If it's not pressure related and you're absolutely sure the radiator has no blockage in the fins, or on the AC condenser in front of it, or between the radiator and condenser, then I would bet it's a failing radiator. It has flow through it yes but it might be partial blockage, very common if anything other than Nissan green coolant (NOT regular American green coolant) and distilled water is put in the radiator.

220F is too hot, normal operation it shouldn't be getting that hot so something is wrong. I doubt it's from sucking hot engine air on that intake.

 

220 is only after flooring it to 60 and mashing the brakes 5 times in a row with the A/c(IMO that’s fine for a car with a trash oil cooler) also, there is no condenser, on the v36, it’s all one unit, I know I probably should use the Nissan coolant Bc it’s better at lubing the water pump but in my other Infiniti’s I run 40% normal coolant, 60% distilled water, and a bottle of royal purple super coolant(I confirmed it works on my built M35) and do a full flush once a year, really the only thing I can do other than pressure test is wait until it’s hotter out and see if it over heats but as of now it’s been fine up to 84 degrees outside so I rlly do think the fans did the trick