Nissan Repair: Overheating problem, lockup torque converter, nissan garage

Question
Hi Von.  I have a 94 terrano 2.7td auto with 82000 miles on it. I recently bought a caravan, and when pulling up motorway inclines it gets very hot with the temp needle going in to the red. I had the coolent changed about 6 months ago at a Nissan garage and since the over heating i took it back and they changed the thermostat, but the problem is still there. Do i need to flush the engine and radiator and how do i go about this or is it beat to but a new rad.
Also with the auto box, when the O/D is switched off it will only change up it to third gear, not go in to top. I think this is the way they designed it but can this be easily changed so i can get forth gear when towing with the O/D switched off.
                    Many thanks, Paul.

Answer
Paul,

I would bet the radiator needs to be flushed and be sure to wash the exterior of the radiator with something like Simple Green or a citrus based solvent and lots of water to get the grime off.

The overdirve is fourth gear and when you take it out of overdrive it will only go to third and the lockup torque converter will not apply.  Now, if you are towing this is the thing to do to keep from overheating the transmission.  Also, I would add a cooler for the transmission and that would help the temperature.  Also, when you clean the radiator add a new cap.