I am stumped and I hope someone can help. My wife (which btw use to post on here years ago with a 03 6MT before life threatening medical issues forced both she and I to sell the 6MT and my all motor 240sx to pay for surgery. She's was one of the reasons I joined this site) drives the 07 Auto Sedan, which since the recent hotter temperatures have brought out some overheat issues. I surprised her with the 07 sedan. We got the 07 in a trade for a Mazda MX-6 and the seller/trader even delivered the car from Fort Bragg area to us outside of Raleigh, NC. Fast forward, the car started to rise beyond the half mark at a stop light and she immediately pulled into a right turn and parked until it cooled down. She threw on the hot air and drove home with no other issues. We started to check things out and took some pictures of areas that may be the culprit. One of the few areas I noticed about the car upon checking it out before the trade was a cracked coolant reservoir. The cap on the reservoir was flimsy and even fell off during the test drive. It was placed back on but when it was delivered the cap was gone. A stopper was put on there which actually fit pretty good and test drove it around during the winter with no issues, so it has remained there since. I went under the car and snapped some pics of the bottom of the radiator to see if there was any damage as this was a salvage vehicle. Dings on the unit that sits just before the radiator but nothing else that jumps out. Also, the radiator cap has no pressure rating...never seen that before. Topped off radiator fluid, massaged the hoses (t stat hose did get hot, so coolant was moving through, top hose wasn't really hot) and let it idle for a while since it seemed to be a little low on coolant. Fans kick on when heat is turned on but I never really saw the fans kick on after the normal drive temperatures were reached. Never overheated but the fans not kicking on still bothered me. Any ideas would be greatly appreciated. Its the 1st VQ35HR in the house hold and it seems alot different that the DE, hell, there isn't even a condenser fan on the bumper side of the radiator lol. Thanks in advance.

 

I'd start by replacing the radiator cap but you can usually tell it's screwed by pulling on that little valve in the very center of it to make sure it opens and closes smoothly, yours almost looks rusted though so it's probably no good.

The radiator fan is TWO SEPARATE fans yes?

There aren't the 3 relays to control fan speed like the DE motors used, instead there's a module that varies voltage to the fans and I think that both fans operate at the same rpm but it will LOOK differently when you're observing the fans spin because the two fan blades have a different number of blades on them.

 

^ Good to know. Appreciate the heads up. I will grab the cap asap.

 

So, I have a new radiator cap and observed both fans kicking on (it took a while, but they both kick on and are operating). It eventually started to get hot so I shut it off. Could the therrmostat be closed? I am thinking thats my next culprit. No leaks from the water pump or signs of issues visually.

 

It's hard to say whether it's the thermostat or the radiator itself, since the temperature creeps slowly that makes me think it's the radiator itself. Usually when a thermostat is failing to open it quickly rises to full overheat HOWEVER the thermostat could just be opening slowly or not fully opening so it's impossible to really tell without pulling the thermostat and dropping it in the correct temperature water and visually watching it open. Dunking it in super hot (250 degree) or hotter water doesn't really work that well because it will almost certainly open at that high of temp.

If it were my vehicle I'd replace both the radiator AND the thermostat, then you've eliminated both as a problem, especially if there's 100k+ on them because they're going to fail soon anyways.

 

Interesting, I'll look into that. What are signs of a bad radiator? Never had one go out.

 

Did you check for debris in front/between the radiator and A/C condenser? Sometimes a lot of leaves, dirt, and what not can stop air flow as well.

 

^ Yes this, in one of my previous Camaro's I ate an entire colony of migrating honeybees on the highway and didn't think anything of it until about 20 minutes later down the highway when I started to overheat because they clogged about half the fins on my radiator and blocked airflow...

 

Its clear. Got to see if the radiator itself has any blockage.