While driving at highway speeds the "n" light on the gear shift starts flashing. This indicates that the automatic transmission is overheating, and that I should pull over to let it cool per the owners manual and a sticker on the drivers door. Which I do - I let it sit for about 5 mins and its ready to go again. However, this is inconvenient and has happened on numerous occasions. I have search all over the internet for a solution, and the only thing that seems to be the solution is to get a bigger pan? It seems costly to do this. Does anyone have any other solutions?

 

Montero or Montero Sport?

First, make absolutely sure you are running the correct ATF and have it at the correct level. Any Invecs transmission requires Mitsubishi Diamond SPIII. Not "SPIII equivalent", not ATF +4, not Dexron with an additive, just genuine Diamond SPIII. If you use anything else, there is probably excessive slipping which is heating the fluid excessively.

Some 2000 Montero Sports had a TSB for the deeper pan update. If yours is one of these, you should get it done. I had the same problem on my 1999 Limited and even though the deeper pan did help, I still had occasional overheating issues. I finally solved it by adding a small auxiliary transmission cooler in-line with the factory one. You can get one for about 40 bucks and it's pretty easy to install. I just put one on my 2003 Sport and it took me all of 90 minutes from start to finish. It's cheap insurance.