It's actually intake temps that do the damage in the majority of the cases.
The whole cooling system does need to be kept in very good condition also though.
On the KZN185 models (intercooled turbo) the radiator has been changed to plastic tanks and larger core. Also the factory trans cooler has been relocated so that the pipe doesn't partially block the lower outlet (like on the KZN130 models).
At our work (Toyota dealership), we recommend people remove the factory trans cooler and fit an aftermarket cooler. And also replace the lower tank with a manual type (no cooler built in it).
1 of the best things to do is either block or, better still, remove the EGR system. This stops the intake temps getting so hot and will reduce the chances or the head cracking.
There are other things that can be done as well to help: viscous fan re-oiled, cooler thermostat (76 or 71 degree - factory is 82), larger free flow exhaust system and dump pipe are just some that make a noticable difference.
Also the factory temp gauge is known to be a very poor sign. There is a modification that can be done that increases the sensitivity of the gauge and is a lot more reliable than factory. (
Temp Gauge Mod)
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