The same thing happen to my Frontier. It was the Fan Clutch.

 

If you didn't use the OEM thermostat, then you should. The X does not like the aftermarket ones for some strange reason.
A heater than only blows heat when the revs are up, is 95% of the time coolant levels.
Could be your spring loaded cap (on the overflow reservoid) that won't hold adequate pressure anymore.

 

I would second the fan clutch. Never had this issue but your description and performed troubleshooting would lead me to the fan not blowing at stops. Thus overheating. When moving air is circulating and cooling the engine. This points to the radiator and general cooling system being operational when air is moving, so the fan and and fan clutch are a good next check.

 

I was considering that before I did the thermostat because I don't really know how to check if my fan clutch is working properly. How can I check that? The main fan spins freely when the engine is off. No binding or wobbling. How do I check if it is working right when running?

 

It will also only blow cool air through the vents (with heater on) until I start driving, then it warms right up.

This leads me to believe you have an air bubble / low on coolant, your pressure caps are not holding, or something is up with your water pump.

 

Make sure your coolant tank and radiator caps are not swapped the pressure cap should be on the coolant tank and the non pressure one on the radiator.I have swapped them by mistake and had issues. Also make sure there is no air in the system there is a small tap on the heater hose by the firewall for bleeding air out of the system it has a rubber cap on it.

 

Been a while but problems still exists. I replaced the fan clutch and now my fan sounds like a 747 taking flight. Not sure if that's normal... It will calm down after a few minutes of idle, but it's pretty loud after driving for a few. I was wondering if it could be the transmission cooler.

My thought process is this;
*It only happens after there is an added load like going up a hill or pulling a small trailer.
*If the transmission cooler is bad, when there is an added load, the transmission has to work harder, generating more heat.

However, I am not familiar with how the cooler interacts with the engine coolant...

Does this make sense to any of you? I am so frustrated with this problem. I am trying to get this vehicle reliable so I can hand it over to my teenage daughter, but I don't want to leave her with an unreliable car.

Thanks again for all the help!

 

Been a while but problems still exists. I replaced the fan clutch and now my fan sounds like a 747 taking flight. Not sure if that's normal... It will calm down after a few minutes of idle, but it's pretty loud after driving for a few. I was wondering if it could be the transmission cooler.

My thought process is this;
*It only happens after there is an added load like going up a hill or pulling a small trailer.
*If the transmission cooler is bad, when there is an added load, the transmission has to work harder, generating more heat.

However, I am not familiar with how the cooler interacts with the engine coolant...

Does this make sense to any of you? I am so frustrated with this problem. I am trying to get this vehicle reliable so I can hand it over to my teenage daughter, but I don't want to leave her with an unreliable car.

When the fan clutch engages it is supposed to sound like a 747. 😁

Now IF the radiator has not been bypassed, then the transmission cooler is inside of it. To cool the transmission fluid heat is exchanged between the tranny cooler and the coolant surrounding it in the radiator. Think of it like running hot water through a hose that is immersed in a bucket of ice water.

Since you are towing or going up hill it is only natural to generate more heat in the tranny, I always downshift, taking it out of overdrive and then maybe going down to 3rd gear. This keeps the tranny from "hunting" for what gear to be in, and it speeds up the engine pulling more air across the radiator helping to keep it cooler.

 

I'm pretty sure you are low in coolant with air in the system. Check the coolant level from the radiator and not from the tank. Fill up in the radiator, drive, and repeat until the level in the radiator remains to the brim. The cooling system is self bleeding so after few runs, your coolant level should be good and solve overheating problem.

 

Were you able to figure this issue out? I am having a similar issue with my ‘08 XTerra.

 

Long thread, but please read; I need help!

I've bounced around the forums and couldn't find one on my specific issue so here goes.

2006 Xterra S, 160k miles

This problem started a few weeks ago.

My commute to work is about 30 miles, takes approx 40 minutes. 60mph average. Mostly highway.

As I am pulling up to my work gate, my temp gauge bumps up to around the 2 o'clock position. Once the gate opens and I start driving again, the temp drops back down to normal and stays there. The same thing happens in reverse on the drive home. About a mile from the house the temp gauge starts to climb at stoplights. Once I get moving again it drops back down and stays. It will also only blow cool air through the vents (with heater on) until I start driving, then it warms right up.

I was told to swap the thermostat, so I did. Problem still exists. I've tried everything I can think of to purge and fill the coolant, and it appears to be filled adequately, possibly slightly overfilled but I can't tell because of how odd the system is.

3 years ago I replaced the water pump, both caps, thermostat, and most hoses. Plus a full system fill with new coolant. No issues with heating or AC until this popped up. No obvious leaks. No obvious damage to radiator. No obvious loss of coolant. It doesn't spit anything out of the reservoir. Both fans appear to be working properly, but I'm not certain on how to accurately test them.

Please, if you have any ideas on what is causing this, I need the help. This is my daily driver, and I cannot afford for it to break down.

I am having a similar issue with my ‘08 XTerra. I have replaced the thermostat, radiator, and temp sensor. Were you able to figure out the issue?