Overheating when towing a boat

I have a 2001 Pathfinder 4x4, and have been towing my 18ft 2500 lb boat around since I bought the truck new. All of a sudden, now I overheat when pulling the boat. It can happen within a few miles. I am not using overdrive, and the fluid level is good. When the truck gets very hot, I am cranking the heat to bring the temp down. The fan is running with the engine. Should I change the thermostat? The tranny fluid runs through a separate cooler into the radiator.

I have a 2001 Pathfinder 4x4, and have been towing my 18ft 2500 lb boat around since I bought the truck new. All of a sudden, now I overheat when pulling the boat. It can happen within a few miles. I am not using overdrive, and the fluid level is good. When the truck gets very hot, I am cranking the heat to bring the temp down. The fan is running with the engine. Should I change the thermostat? The tranny fluid runs through a separate cooler into the radiator.

I tow about the same weight boat with my 97 and have never had any problems with overheating. How is the coolant condition, have you changed it recently? You might try cleaning the radiator and tranny cooler with a water hose, spray from behind towards the front of the car. Thermostat would be a good bet but I would think you'd be running a little hot even not towing if it was stuck completely or partially closed. Have you noticed the temp any higher in normal driving?

The coolant level is good, it was flushed this past weekend by a Nissan tech. The problem is still there. Gets very hot when towing, runs perfect temps when not towing. The boat/trailer are 2500 lbs, should be well within the limits. I am worried that the tranny may be getting too hot...

The coolant level is good, it was flushed this past weekend by a Nissan tech. The problem is still there. Gets very hot when towing, runs perfect temps when not towing. The boat/trailer are 2500 lbs, should be well within the limits. I am worried that the tranny may be getting too hot...

Is it the engine temperature that is reading hot or are you also seeing the A/T temp error. I've heard that off-roaders see the A/T temp warning right before the transmission fries so it's kind of worthless. I would recommend draining the transmission pan to take a look at the condition of the fluid, mine drains about 4 qts of the total 9qts in the system but should tell you something about the condition of the fluid and whether it is running hot.

If you decide to change thermostats, plan ahead. My 2001 started overheating sporadically without towing anything. I have now found out that there are 2 thermostats and one of them is very hard to get. Mine has been in the shop for over 2 weeks waiting for the backordered front thermostat, and the rear thermostat replacement is a major operation.

I have now found out that there are 2 thermostats and one of them is very hard to get.

Thought your mechanic was crazy until I saw some documentation on this, Nissan calls the second a water control valve but sounds like it is actually a thermostat. This only applies to the newer pathfinders with the 3.5L engine.