Rust (Oxidation) on 316 Stainless Steel BBQ Rangehoods can have many origins. The most common is closeness to Salt air but there are other reasons such as cleaning your BBQ Rangehood with the wrong cleaner such as steel wool or any Caustic Cleaners.

Steel wool may add minute particle of steel to the 316 Steel causing it to begin to Rust. Caustic cleaners may contain Chlorides or Alcohol & damage the Chromium layer

1. Removing Oxidized stains on your BBQ Rangehood can done by using a paste made from  baking soda & water. One tablespoon of baking soda to 2 cups of water ( distilled if possible)
2. Use a clean cloth rub the baking soda paste in the direction of the grain.This may take some effort but should remove the soiling oxidation.
3. When cleaned rinse with clean water (distilled) on a soft clean cloth.
4. Coat with baby oil.