Dot 5 or Dot 3?

[wazzabie]

I have not changed the brake fluid on the K5 in over 25 years. Now that it is running again I'm going to change out the fluid. I'm wondering if I should go with Dot 3 or Dot 5?

I went thru the fuel line and replaced it since the fuel line was rusting from the inside. My plan is to replace the brake line and brake hoses.

 

[Wes Harden]

No dot 5. Unless you change flush and change all the major components.

Dot 3 or 4, can be used together. Dot 5 can not be 3 or 4

 

[Fastereddie]

No dot 5. Unless you change flush and change all the major components.

Dot 3 or 4, can be used together. Dot 5 can not be 3 or 4

I thought that was dot 5.1 or do I have it backwards?

 

[Wes Harden]

Dot 5 is silicone based and does not play well at all with dot 3 or 4, if you mix dot 5 with either 3 or 4 you will be replacing all your brake components in short order.

Dot 5.1 is new. It can be mixed with 3 and 4. Dot 5.1 has higher affinity for water than 3 or 4, and is more expensive. My choice would a quality dot 4 with High boiling point.

 

[scoots90245]

MIX BRAKE FLUIDS?​

Yes, but with certain exceptions.
Brake fluids can be mixed only if the fluid that you add to the system belongs to a higher grade.
For example, a braking system that has a brake fluid DOT 3 specification can use a DOT 4 or a DOT 5.1 fluid. Also, a system with a DOT 4 can be topped up with a DOT 5.1 without bleeding the system.
However, never top up a DOT 4 system with a DOT 3 brake fluid. DOT 3 won’t be able to meet the temperature requirements because of its lower dry and wet boiling points.
Once again, do not mix DOT 5 with any other type of brake fluid because of its silicone-based composition.

 

[scoots90245]

GLYCOL BASED​

Brake fluid DOT 3 uses glycol ether as a solvent and a conventional brake fluid used in vehicles produced up until the 1990s. It is suitable for all brake systems and all driving conditions.

Brake fluid DOT 4 uses glycol ether and borate ester compounds which improve its performance compared to DOT 3. Cars produced after 2006 use it as a standard. Like its predecessor, it is suitable for all brake systems and driving conditions.

Brake fluid DOT 5.1 uses glycol ether and borate ester compounds but has an enhanced performance like the silicon-based DOT 5. We can say that it is a non-silicone version of DOT 5 but compatible with DOT 3 and DOT 4 types of braking systems and fluids.

​

SILICONE BASED​

Brake fluid DOT 5 is a silicone-based fluid making it incompatible with anti-lock braking systems. Additionally, DOT 5 cannot be mixed with other brake fluid types and unlike other fluids, it does not damage the paintwork.

This fluid is engineered for demanding applications like military vehicles and extremely cold climates.

 

[Wes Harden]

USPS uses Dot 5 in all their hydraulic brake vehicles, have for years. I use dot 4 in everything. If you can find Motorcraft dot 4, it advertises a higher boiling point then any other, close to dot 5 temperatures.

 

[Cucv_M1008]

I run dot 5 in the cucv.

 

[Barrman]

What is your intended use of the K5?

If you want to refresh the entire brake system and not touch it again for another 25 years. DOT 3 or 4 as mentioned above is perfect. As long as the system stays sealed no moisture should get in and things will probably last 25 years before rusting out from the inside.

Hi performance brake pads, lots of mountain driving with a heavy right foot? Good quality DOT 4 or 5.1. You can probably still let it sit a very long time and not worry about it.

High performance brake pads, lots of mountain driving, lots of water and you enjoy flushing the entire brake system every 5-10 years. DOT 5 or as the military calls it Brake Fluid Silicone won’t absorb moisture, it won’t boil out under extreme heavy use and no part of the system will ever rust on the inside. The down side is you have to flush out what was there before, it cost more and flushing every few years is highly recommended.

I run BFS on all of my non ABS vehicles and am glad of it. Good quality DOT 4 in all my sports car type vehicles.