New to forum, help needed! I have a 2000 Nissan Maxima. I am having a problem with overheating issues. The car runs nice and cool if I'm driving in the city, once I get out on the hiway at 65, 70 Miles an hour in about 10 Miles it starts to overheat. I have changed the thermostat and replace the water pump, put new hoses on, flushed radiator twice now,and still having a problem. Any thoughts on what might be the issue. I live in AZ where it is currently 115°, but never have had an issue before. Thanks for any help

 

I would start by making sure your radiator fans are kicking on when it reaches temp. Secondly, are you sure you installed the thermostat correctly? OEM thermostat or aftermarket?

And have you burped the system for air?

 

Thanks for the reply. The fan seems to working correctly, thermostat was installed at a shop, I assume it was done correctly. I did burp it best I could, I am going to try an Get the car on a incline and do it a little better. It just doesn't make sense to me why it would only overheat on the freeway at a high-speed. I was just thinking I'm missing something that's not one of the obvious problems maybe some kind of sensor ,relay or maybe the air conditioning evaporator or something.I just I'm perplexed of this problem, but I thank you for the Info I'll keep trying

 

Did you install just the hermostat, or thermostat housing with the thermostat pre-installed? If just a thermostat, you may have installed the thermostat upside down, which affects the operation of the tiny relief port and cooling.

 

When it's starts running hot on the freeway, crank the heat at full blast and see if it helps the temps go down. It should. If not, you may have a clogged heater core. But do the easy stuff first like burping it on an incline.

And are you sure your coolant levels are up to snuff?

 

Another possible issue is that your radiator could be failing and is clogged. At high speeds, it can't cycle the fluid fast enough which results in overheating. Luckily, radiators are cheap and easy to replace on this car. Also, when was the last time the radiator cap was replaced? Has it been tested to see if it holds the right pressure?