Choosing the proper brake fluid for your Land Rover falls into one of two categories. You can do what the manual tells you and only use Castrol, or you can learn about brake fluids and choose what best fits your needs. Take note: There have been reports of fluids other than castrol causing problems with seals on our trucks. Note that the service manual calls for these seals to be replaced periodically anyway for safety. Different drivers have different needs when it comes to brakes. This article will attempt to arm you with the information that you need to make an informed decision.
DOT rates brake fluid by its boiling points. When brake fluid is fresh (DRY) it has a higher boiling temperature. How does it boil? Well, when you apply your brakes, you create heat from the friction between the brake pads and the disc. Some of this heat is transferred to the brake fluid. If you are heavy on you brakes, or do a lot of stopping from high speeds, you will get your brake fluid quite hot. If you get it above its boiling temperature, it boils, and creates air bubbles. This makes your brakes feel mushy and can lead to brake failure. Keeping the fluid from boiling is of paramount importance.
The other primary problem with brake fluid is that it is hydroscopic, meaning that it naturally takes on water. When it takes on water it boils MUCH easier to boil because water boils at a very low temperature (212F). When the fluid takes on water it is referred to as wet. When brake fluid is left in the system for more than a few months, it takes on water progressively. Some fluids take on water more readily than others.
This leads us to the DOT ratings. The DOT requires that brake fluid manufactures disclose the high and low boiling points of their fluid on the container for comparison. While this is all well and good, what it doesn't mention is how LONG you have until you reach the lower, wet boiling temperature. If you just pick your fluid by the wet points, you will be much safer. Or if you prefer, you can use the dry temperatures and change your fluids often, every 6-12 months.
DOT says that the MINIMUM specifications for DOT 3 are 401 dry and 284 wet. Minimum for DOT 4 is 446 dry and 311 wet. DOT 5 fluid is functionally different from DOT 3 and 4 and is NOT recommended for use in ABS systems. It tends to aerate easily which causes bubbling when the ABS system activates.
If you need more information you can check the following links:
SHOTimes FAQ
HowStuffWorks