I have a 2002 Pathfinder Chilkoot edition, under certain circumstances my engine overheat. Let me explain what happened in the last few years and hopefully you guys can help me out since no one seems to find the problem

Ok so it started 4 years ago my truck overheated, on a hot day around 80F outside, i was driving on the I-87 in the adirondack (lots of high hills) the funny thing is that when i was driving on flat road everything was okay but when i started to go up it was overheating so i was turning on the heater to cool it down. Strangely on my way back home during the night no overheat at all. I had an extended warranty so Nissan changed the radiator. For the rest of that year everything was fine.

The next year it starts overheating while i was stuck at the customs waiting to cross the border. Started the heater. The minutes i started rolling the temperature cooled down. I had it checked the next day and they could not reproduce the problem.

It does that very often when the temperature is 80F + and either i am asking more the engine either going uphill like in the adirondack, towing or pure simple being stuck in traffic (going forward and have to stop often). Each time it takes around 30 minutes to 1 hours of driving before anything happen, last year i had everything checked again, they ruled out the radiator, i had the thermostat changed and the coolant flushed. And it still overheated again

It is a very odd problem and i myself is no mechanic, i just know that if i go on a "flat" road my truck do not overheat even in temperature 90F.

I love my truck and want to keep it but it is very annoying during summer to have to put on the heat on a very hot day. I would love to know what could be wrong so i can have it checked. Could it be the transmission? Because from what i can see the radiator fan is connected to the timing belt and it work when the engine is running.

Thank you, if there is info you need let me know

My first thought was the fans not kicking on, but you ruled that out. My next thought is you have an air bubble in the radiator, presumably from the radiator repair, causing a random blockage. I don't know the exact procedure for our vehicles, but you might research "burping" the coolant.

2002 Pathy's don't have timing belts. It sounds to be like you have a faulty fan clutch. At highway speeds, the air forced through the radiator core alone is sufficient to cool the engine's coolant. When a vehicle is under high load, standing still or at low speeds, the fan clutch will start to engage the fan, which will pull the required air through the core to cool the coolant. So, if the clutch is failing to engage the fan enough to reach proper speed, it won't pull enough air through during these conditions and thus overheating will occur.

slownlow43 wrote:My first thought was the fans not kicking on, but you ruled that out. My next thought is you have an air bubble in the radiator, presumably from the radiator repair, causing a random blockage. I don't know the exact procedure for our vehicles, but you might research "burping" the coolant.

Thats what I was thinking as well... Little trick I've used on other vehicles... Jack the front end of the truck up, Run the engine (cold) with the rad cap cracked open or completely off, Run until engine heats up. Durring about 10-20min if there is a bubble in the system it will work it way up to the top of the rad and burp itself... Also could be a bad Thermostat as well, in that case the burping trick may not work..