... It looks like my montero comes with a stock cooler and it also runs into the radiator as well. So the suggestion would be to add a 2nd cooler with a fan, and leave the oem cooler without a fan?
I did a full flush and the fluid was brown, didnt smell but was not red. I have a trip coming up this weekend ill see how it goes. You do have my worried about my radiator now though.
No, you're not supposed to run multiple coolers. Besides causing flow restrictions, multiple coolers and all the line will themselves raise the temperature of the fluid. For all that I've ever heard or read, this is considered pretty much universally to be a 'bad idea'.
For me - I'm building a '99 Sport on 37"s with the same transmission you have - I'm going to pull the A/T stuff out of the radiator and run a big aftermarket in front of the condenser. If it'll fit and if it doesn't restrict air flow to the condenser and radiator. Plan 'B' is a big cooler with a fan mounted, uh, somewhere. I haven't figured the 'where' out yet.
That was the decision I arrived at after pouring though Pirate, 4MUD, the AW4 forums, towing forums and talking to the A/T shop that builds these for off-road use and talking to the Jeep shops.
What you're describing sounds a lot like what I've seen out with the Cherokee/Toy guys off road. The idea behind the in-radiator cooler is that it warms the fluid up when its cold, and cools the fluid when its hot. That's the one benefit of the in-radiator cooler over a passive A/T cooler - it works even when you're standing still. Mostly.
You MAY be having a problem with the radiator. I'm religious when it comes to fluid flushes but most people are not and that leads to scale and crud build up especially in the radiator and since the in-radiator cooler isn't that efficient it doesn't take much to affect it.
I would run an OBD scanner and monitor ECT over a good period of time under various conditions and see if the average coolant temp is elevated. If so you could kind of infer that the radiator is either dirty internally and/or externally and needs cleaned - assuming of course, that everything else is sound.
Which brings up something else to check. Either the condenser or radiator or both may be full of bugs, leaves, dirt, mud, etc. restricting air flow just enough that you're starting to see the beginnings of a cooling problem. Easy enough to fix - remove the radiator and take a garden hose or a pressure washer on low and flood water through the fins in reverse of air flow. Leave the condenser installed and do the same for it before you reinstall the radiator. This is probably something that is long overdue in anyway.
In any case, if I were going to off-road the AW4 I would get a real cooler and use that. Its a good transmission and the only time anyone really has issues with it is when its overheated. I know guys here in CO that run 37, 38 and 40 inch tires on it and have for years without issue but they run big coolers.