Strange Temperature Problem 904runner

[hanko]

Hey everyone: I have a 90-4runner-6-auto. I can drive it for hours in any climate and the temperature gauge will always read normally in the middle. If I stop and shut the engine off for about ten minutes and start it up again, the temp gauge shoots right to the red. It goes right down to the normal setting after only about a mile of driving and I'm good to go again. I've noticed alot of coolant backed up in the plastic tank when I check under the hood. Any suggestions as to what it might be ??? Hanko