How can I remove rust from a 50 year old outside thermometer?

Navel jelly (from a good hardware store). Slow work with a toothbrush and old T shirt scraps. FINE steelwool....but be careful! You might reduce it's value!! OLD RUST is SO "IN"!

WD40 works too, be sure to wear plastic/vinyl gloves.

Navel jelly- from a hardware store.

Brasso it’s a cream cleaner it cleans very well try using that to take the bus stuff it does clean was very well

If the mercury thermometer is intact, mark the 0 degrees spot on the glass before removing the thermometer. Then soak the metal in white vinegar overnight. The mild arctic acid in the vinegar dissolved the rust. However, you must coat the cleaned metal with a light coat of mineral oil or it will quickly rust again. Then remount the glass thermometer in its original position.