gas tank

this is an example of the early model gas ventilation tank...i hear that a quick fix on any white non painted plastic is soft scrubb to remove scraches and stains. It works and it works quick.

Source: http://wiki.answers.com/Q/How_do_you_restore_white_automotive_plastic#ixzz1jsViolAd

White plastic turns yellow over time due to a chemical reaction that occurs when it is exposed to light, oils, etc. There are a couple of different ways to get rid of this discoloration, ranging from easy to more difficult. Look through the methods to find one that works best on your particular project. Some are more practical for larger projects, while others are ideal for smaller pieces.

Bleach Method

You Will Need:

• Bleach
• Water
• Bucket or large bowl

Steps to Whiten the Plastic:

1. Fill a bucket or large bowl with one part bleach and one part water. Fill it enough so that it will cover the yellowed pieces when they are submerged.
2. Allow the items to soak until they return to the original white color.
3. When they have reached the desired level of white, remove from the solution and rinse with clean water.
4. Wash with a mild detergent and allow the pieces to air dry completely.

Sanding Method

You Will Need:

• Superfine sandpaper
• Water
• Soft cloth

Steps to Whiten the Plastic:

1. For this method, the goal is to lightly sand off the top layer of the plastic that is discolored to reveal a new, white layer.
2. Begin by wiping down the plastic piece completely.
3. Rub the superfine sandpaper over the surface to remove the yellowed portions.
4. When finished, wipe with a moist cloth to remove any dust.

Comet Method

You Will Need:

• Comet
• Water
• Bucket or large bowl
• Dish detergent
• Scrubbing sponge

Steps to Whiten the Plastic:

1. Start by moistening the plastic pieces.
2. Place some comet on the scrubbing sponge and start scrubbing.
3. This requires plenty of elbow grease and time, but will take the yellow out with some scrubbing.
4. When the yellow is removed, wash the piece in water and dish detergent.
5. Rinse completely with clean water and allow it to dry.

Peroxide Method (for ABS plastic)

You Will Need:

• Hydrogen peroxide
• Oxy laundry booster
• Sunshine or UV light
• Water
• Bucket or large bowl
• Rubber gloves
• Goggles

Steps to Whiten the Plastic:

1. Begin by protecting yourself with rubber gloves and goggles.
2. Fill the bucket with hydrogen peroxide.
3. Add ¼ teaspoon of Oxy laundry booster for each gallon of peroxide.
4. Place the yellowed plastic pieces into the solution and allow them to soak.
5. The soaking time will vary with most pieces whitening in 2-6 hours. The mixture will last for up to four days before it needs to be replaced. Retr0Bright has also developed a way to make this into a gel that can be spread onto the plastic. This is especially helpful for larger items.
6. Set the items under a UV light or out in the sunshine.
7. When the item has reached the desired whiteness, remove and rinse thoroughly to remove any remaining cleaning products.
8. If necessary, wash with dish detergent and water.

Additional Tips and Ideas

• While bleach can be an effective color remover, it may weaken the plastic over time.
• Painting the plastic pieces (if they’re not food storage containers) with a clear acrylic varnish will help prevent them from turning yellow again.
• For plastic pieces that are discolored from food dyes, see our article about How to Clean Food Dyes from Plastics.

Source - http://www.howtocleanstuff.net/how-to-whiten-yellowed-plastic/