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Silicone or glycol? What do you use?

Silicone or glycol?  Each has its’ pluses and minuses.  Let’s look at both.

Regular brake fluid can be a good paint remover. Of course, if you plan ahead for a spill it isn’t that big a deal. But is silicone brake fluid the be all, end all cure for poor paint surfaces and poor maintenance technique? Consider that while silicone will not remove paint, it can lead to what is called “cupping” where paint will not adhere to the surface being painted. So it could be a concern if you have to do any touchups at a later time.

How to determine if you have silicone or glycol fluid? “To determine if an unknown sample is glycol or silicone fluid, put some in a glass jar. Add water a drop at a time. Glycol fluid will dissolve in water with slight milkiness, but silicone fluid will form two distinct layers, with water on the bottom. Silicone stays clean and clear in a brake system, but old glycol looks rusty after years of use. The purple dye transfers from silicone to glycol fluid if you mix them together. ”

This guy has a pretty good site and it seems fairly balanced in the glycol vs. silicone discussion.

Which to use? Appears to settle upon a few factors:
1. If you preventive maintenance skills are lax then the use of silicone is likely your best bet. If you are capable of changing your brake fluid every couple of years then perhaps glycol is best for you.

2. If you can’t fill the master cylinder without spilling it all over your painted surface then perhaps silicone is the way to go. However, be forewarned that while silicone doesn’t eat paint it keeps it from adhering to the surface and leads to “cupping”.

3. If you have more money than time then silicone is perhaps best for you. In most places the same quantity of silicone is several times the cost of glycol. But on the flip side you will need to replace your glycol several more times than silicone.

4. Do you drive your jeep thru water, wet roads when it rains? The jeeps’ like many brake systems are open to the atmosphere. Glycol is designed to absorb moisture and has inhibitors designed to reduce corrosion. Silicone is not designed to absorb water. Moisture will pool in silicone and can lead to corrosion.

5. Spongy feeling. Silicone has a higher compressibility then glycol which can lead to a spongy brake pedal sensation. Silicone has a slower pour rate (higher viscosity) than glycol. This may explain why it can be difficult to bleed the air from silicone equipped brakes. Once air is mixed into silicone (bubbles) it can take a long while to bleed it out.

Check out these articles:
http://www.adlersantiqueautos.com/articles/brake1.html
http://www.adlersantiqueautos.com/articles/brake2.html

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