LEAKY CAR RADIATOR:
I had a shitbox car once I used as a work car to park in the shitty side of town (even left the doors unlocked) It had this tiny pinhole leak in the radiator that probably occurred from internal corrosion. It was nearly impossible to even locate and there was no way I'd invest a dime to fix it. So:
-Add a teaspoon of plain black pepper. It will flow to the leak and plug it like a barrier. If dislodged, other pepper grains floating around will take it's place.
-Add one egg white. Once the engine gets hot it will cook the egg white into little rubbery plugs. Makes a better seal than the pepper but as I recall doesn't last quite as long.
*I can't remember, but one of the above "fixes" would last about two weeks before I had to do another cheap fix again. Not bad.