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Car overheats while under load or at a stop

2000 Nissan overheats while under load (climbing hills or grade) or at a stop The AC can be on or off makes no difference. 140,000 miles Cools down when driving on level grade or down grade.
New radiator, thermostat, hoses and fans. All appear to be work fine.
Burped system appeared to help but issue continued. Just took longer.

Are you sure those fans are actually working? Get the car hot, AC off and one fan should come on as the temp rises before it overheats. Turn on the AC and the other, or both should come on. Both are controlled by relays and one fan is triggered by a temp sensor in the cooling system. Plus the wiring. All has to be in good shape or the fans won’t run and the symptoms you describe will happen.

Yes and they were new. Found this image and followed i. Seems to have fix the issue.

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Good for you, sounds like it just wasn’t bled of all the air. The air bleeding instructions I expect advised you to turn the heater to max also during the bleeding process, otherwise you can get air trapped in the heater loop.