87 4runner help

What could have happened???? I took my 4runner for shocks and rims and she ran great as always but when I picked her up she was smoken a little and was running rough ....I drove the 5 miles home to find she was over heating and looks to have a blowen head gasket? she ran geat when dropped off ....How did this happen??? She only has 15,000 on a rebuilt motor....She has shown no signs of being hot or anything, until I picked her up from the tire shop......Help and thanks

I bet they took it for a test drive...

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