Strange Overheating Issue

[GX470]

A little bit of background: I have an '04 Pathfinder SE 2WD with almost ~175k on the odometer. Been a very great & reliable car since I was able to made it up to that mileage from ~4k with only basic regular maintenance and no major issues or repair whatsoever. Aside from periodic oil change, some other services include air & cabin filter (changed every year), drive belts, tires & brakes, battery, spark plugs (changed at 100k), 2 up-stream O2 sensors (at ~160k) and all the fluids drained n refilled every 50k (coolant, transmission, brake, steering and even the differential). That's about it. Everything else is still original up to this point.

Here comes the issue. Everything had been fine until the other day while I was driving with the AC on, I noticed the temp gauge started climbing up. Didn't let it go all the way to the max, I immediately turned off the AC, put the heater on full blast. It did help bring the temp back down. Pulled over and checked under the hood, coolant level was normal, no leaks anywhere, fan was turning and no strange noise.

Went home and did some research and troubleshooting. New thermostat, radiator cap, fan clutch (all dealer OEM parts) and a complete coolant flush (even though, I already did that at 150k). All the above didn't seem to fix the issue. I don't think the radiator is clogged because I notice engine runs fine for the first ~30 mins before overheating. Doesn't matter if idling, in traffic, or on freeway. I don't think the head gasket is cracked either since the fluid was very clean when i drained it out.

This issue is very strange from what I've read about overheating. Now, I'm really lost and don't know where else to look for. Any opinions or inputs would be very appreciated.

[Slumpert]

You have a secondary thermostat that might be failing.

Might might just have a very dirty aircon or raditor coils. There was litterally trash between the two when I changed my rad out and there is no easy way to really clean them installed since they are sandwiched.

If it all looks decently clean then I would suggest replacing the radiator.

[Petergunn]

I am having this same issue. I can drive all around town all day without the A/C on.... no issues. I can turn the A/C on within just a few miles I notice the temp gauge starting to climb a bit. I can change to heat, vents and recir and the temp starts to drop back down. I have a 1999 QX4. There is ample room between the rad and a/c coils to see that there is no trash or blockage. I was thinking maybe the a/c coils or rad needed the fins cleaned...I made sure all the air was out of the system after I replaced a hose. Any other ideas?

[attofarad]

Just to elaborate on Slumpert's comment:

There is a second thermostat, I think called the "water control valve." It mounts into
the crossover tube, which is between the engine and the firewall. It opens at about 30F higher temperature than the main thermostat. The one on my wife's 2001 QX4 was found to have failed, somewhat bizarre looking, when the crossover tube was removed to replace a leaking seal.

However, I don't see how this would cause your problem.

[attofarad]

On the other hand, maybe the water control valve IS a factor.

See post #2 in this thread:

water-control-valve-t459969.html

[GX470]

Just to elaborate on Slumpert's comment:

There is a second thermostat, I think called the "water control valve." It mounts into
the crossover tube, which is between the engine and the firewall. It opens at about 30F higher temperature than the main thermostat. The one on my wife's 2001 QX4 was found to have failed, somewhat bizarre looking, when the crossover tube was removed to replace a leaking seal.

However, I don't see how this would cause your problem.

You have a secondary thermostat that might be failing.

Might might just have a very dirty aircon or raditor coils. There was litterally trash between the two when I changed my rad out and there is no easy way to really clean them installed since they are sandwiched.

If it all looks decently clean then I would suggest replacing the radiator.

Thank you guys for your advice. I did try to look for that "water control valve", but its location doesn't seem to be easy to get to.

Anyway, after trying blowing the debris out of the radiator fins didn't help (It wasn't that dirty, either), I decided to bring the car to the shop. They were able to do perform better testing and diagnostic. They even took a look at the water pump area (covers was opened). Don't know how they did it but eventually they found out the radiator was the culprit. New radiator dropped in and problem was solved. Been driving the car with AC on for a few days now and no more overheating.

Due to this incident, I've pretty much replaced the whole cooling system components. kinda costly but hopefully it would give me at least another 100k trouble free. Cross my fingers that water control valve and the water pump won't fail anytime soon.

Thank you all again. I appreciate your inputs.

[GX470]

I am having this same issue. I can drive all around town all day without the A/C on.... no issues. I can turn the A/C on within just a few miles I notice the temp gauge starting to climb a bit. I can change to heat, vents and recir and the temp starts to drop back down. I have a 1999 QX4. There is ample room between the rad and a/c coils to see that there is no trash or blockage. I was thinking maybe the a/c coils or rad needed the fins cleaned...I made sure all the air was out of the system after I replaced a hose. Any other ideas?

Your situation is very much similar to mine. And mine was getting worse even without the AC. Turned out it was my radiator that blocked the coolant flow. kinda surprised because the radiator looked clean from the outside and I flush the cooling system every 50k. I guess it's because it's 10 years old.

From my experience, I would suggest replacing the radiator first if it's too old. I recommend change out the radiator cap and the thermostat as well since they are cheap and easy to get access to. It would save you some headache down the road. Let me know the result.