My car began overheating and nobody could figure out why. Three different people looked at it and conjectured. . .I put it in a new thermometer (at least it was cheap) to no avail.

Well, finally, the last shop kept it for a couple days and diagnosed it as a cracked seal on the radiator cap. Part? $5. Labor? $55. Dude, seriously?

Well, it fixed it, anyway, and I haven't had any radiator problems since. So don't overlook the really dumb, obvious fixes!