As far as I'm aware the overheating woes associated with the auto 90/95 series is a larger issue with the TD's and not found so much in the D4d's. I'm not aware that anyone ever found a diffinative answer as to why the TD models are so prone to overheating, except that Toyota may have inadvertantly designed the cooling system with little or no room for the vehicle getting older and putting on a few miles. People have looked at all sorts that I've read about to cure or improve the possible issues that may cause the overheating from replacing the rad for a new one, replacing the water pump, flushing the system through and replacing the thermostate all as a just in case any of these may be the cause of the overheating troubles.
My understanding of the reasoning behind fitting a separate stand alone cooler for the auto box is to remove the heat load of the auto box from the finely balanced engine cooling circuit. It's only more recently I've read people talking about the intergrated OE auto box cooler failing and the auto box oil becoming contaminated with water. I've have to say that if Swampy had not come with a separate auto box cooler fitted I would have probably not fitted one myself!
The single most effective thing that I've read about notably improving cooling on an older higher mileage 90/95 series was either servicing or replacing the Viscouse fan coupling. Some thing that in the most part gets overlooked as just working because it's going around.
if Swampy had been an older high mile 3.0TD auto without a separate auto box cooler fitted I would have probably fitted a new rad and either replaced or serviced the viscouse fan coupling.
Don't quote me and I'm very happy to be corrected, but I don't think that they have a problem with the head. They seem to have a finely balanced cooling system that can in some cases easily overheat causing head damage.
You could always buy a manual as they don't appear to suffer from the overheating woes of the auto. Probably because the cooling system on the manual is not having to cope with the heat load of the auto box cooler as the viscouse fan coupling slowly becomes less efficient with age.
