Originally Posted by MikeColangelo
There is some misinformation in this thread.
Dot 5 is silicone based, not Dot 4. Dot 3 and Dot 4 brake fluids are both glycol based.
Don't use Dot 5 in your truck, use either Dot 3 (recommended) or Dot 4. The main difference between Dot 3 and Dot 4 brake fluids is that Dot 4 has higher wet and dry boiling points so it's better than Dot 3 for applications where the brake fluid can expect to get hot, such as on race cars. I think you'd be wasting your money using Dot 4 in your truck, assuming that you are driving it like 99.9% of F-150 owners. It won't hurt but isn't necessary.
X 2: Also (just to add a little information here), the DOT 4 is a little less likely to draw moisture (a common trait of brake fluid). If you have a vehicle that sets a lot, the DOT 4 is a good bet. BTW, Wal-Mart sells the DOT4 for just a few pennies more than the DOT 3. I use the DOT 4 in my '91 Mustang, because it doesn't get out much between cruises and car shows.