Hey guys. New potential Pathfinder owner here. Looking for something that can tow a nice sized camper, around 5100 lbs. I wanted to get a general consensus as right now i am looking at an 05 and an 07 model.

I assume that if this issue has arisen in any car, then it would have needed to be fixed or it would be able to drive, assuming the tranny sustained massive enough damage. Is there a way to check if either of the original parts has been replaced?

Also, if i do decide to grab one, and the bypass job isn't done, can i just bypass, or should i bypass and go through an aftermarket cooler? I live in Montreal, Canada, where it gets really cold in the winters, but not overly hot for too long in the summers.

I do plan on towing whatever camper i end of up for distances of less than 500km at any given time. Maybe a trip to the US which may be around 1000km each way. just want to make sure the tranny would stay nice and cool.

And finally, just looking for overall satisfaction with the vehicle. I've read a lot, and most are positive reviews, but a lot of people aren't so impressed with overall durability and build quality.

TIA

I assume you are referring to the cross-contamination issue. The first thing I would do is get a CARFAX to check the history of any vehicle you may be considering purchasing. That should tell you if there was a transmission repair if it was done at a dealer or registered shop. Original radiators will have a Calsonic sticker on the top of the radiator tank with the part #'s 21460-EA215 or 21460-EA265. 21460-9CA2E may show up on Nissan replacement radiators, which is where the gray area comes into play. Some of the early versions of this part # have failed, but the later ones appear to be okay. If the radiator was replace after 2010, it should be good. Original radiators also have "NISSAN" molded into the tank on the passenger side. Aftermarket replacement will not have the Calsonic sticker on the tank. The bypass method has worked on many vehicles, but it does sacrifice some cooling ability in extreme conditions and also eliminates the radiator's ability to warm the fluid quicker and maintain it at the ideal temperature of 175-200 degrees F. If you'll be in Canada and will also be towing over 5000 pounds, I think it would be best to replace the radiator (if it's original) and make use of the radiator's internal cooler. Aftermarket radiators can be had for under $100 for Ebay units or for $350, you can get an all-aluminum CSF radiator from Stillen.
Other recommendations for towing that much weight:
-get a weight distributing tow hitch
-install Airlift 1000 air bags
-install a set of monotube rear shocks, like Bilstein HD 4600's

As far as the vehicle, in general, 2005-2007 are the most trouble-prone, but buying one now may mean most of the "bugs" have been already fixed. The common issues outside of the radiator concern include Fuel Sending units that start working erratically and trigger the CEL and upper timing chains cutting through the plastic tensioner faces due to poorly stamped chain links, which doesn't affect every vehicle nor does it occur at any specific mileage. The problem starts by causing a whining noise that sounds like a bad power steering pump and gradually gets louder over time. Front sway bar mount bushings can allow the sway bar to push through to the cross member and make a knocking noise, but Nissan has corrected the issue with new bushings and it's a cheap repair. Headlight performance could also be better.
That said, many people are happy with their R51 Pathfinders. I bought my 06 LE about six years ago and have been very happy with it. Gas mileage is okay at 17.5 MPG combined and it doesn't seem to change whether I use regular or premium fuel. Maintenance is simple (although they could have made the oil filter a little more accessible). The ride is good on highways, but it gets a little unsettled on bumpy roads, which is more due to being a body-on-frame design than anything else. Even with my bad back, I'm comfortable in the seats even on long trips. I'm happy with the factory Bose system. If you can afford it, 2011 or 2012 would be the best years to buy as most of the issues of the early models were worked out by then.