Take a look at the transmisison dipstick, when water or coolant gets into a transmission it will turn foamy and light colored- very similar to a strawberry milk shake in color and appearance.
Transmission shifting problem on http://schematicsdiagram.blogspot.com/2012/01/transmission-shifting-problem-on-toyota.html
Many car users get the coolant system flushed due to this.
As far as flushing the coolint system- you will have this all open when replacing the belt. I recommend you remove the thermostat, turn the key tio "ON" and turn the climate control to HOT setting to open the heater core valve. Then use a garden hose and flush the block and heater core very well via the top hose. Take note that there is a block drain for the cooling system on each side just under the exhaust manifold on each side, it has a 10mm jam bolt to plug the drain cock.
On the older Landcruisers NO there is no other point of these fluids interchanging. On the newer ones (2005 and up) there is a coolant line to the trans so the radiator is going to be your issue here. I have to be honest with you that I have NEVER seen that happen on the landcruiser/LX470 from this year range with a factry brand radiator....very odd indeed. You did not reply back to me yesterday to indicate if you have signs of transmission contamination or not, if you do have this issue I highly recommend you drain the fluid, drive it, then hook up a flush machine to the transmission, drive again and then drain/fill again. These can be a real nightmare to clean out. The transmissions on the 1999-2003 have known issues anyway so you do not want to give this transmission another reason to act up.
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