DOT 5 Brake Fluid

I have started using DOT 5 fluid in all my vehicles. This is a silicone based racing fluid. The boiling point is the same as DOT 3 or 4 but it has other advantages. It is compatible with most seals, it doesn't absorb moisture and it won't damage paint if spilled. The inability to absorb moisture ensures the boiling point won't be affected and eliminates the possibility of a vapour condition in the system. It also helps eliminate the corrosion experienced when moisture is let gather in the system. You need to completely flush the system of the old fluid as they turn to a brown sludge if mixed.

 

This could be a hotly debated topic, put whatever you wish in your vehicle/bike etc but there are negative issues associated with silicone brake fluids. Yes, they won't damage paint, however, it is VERY important to remove all traces of glycol based fluids prior to switching, which in my opinion, can only be done with a complete overhaul of all components in contact with the fluid. It will not absorb moisture, so if moisture does get into the system, and it will, it will remain as moisture, which will rust, and contribute to a spongy feeling pedal. Glycol based DOT 3 and 4 are hygroscopic, they will absorb water which will lower the boiling point but it will not allow the moisture to sit like oil and water. Most every European/Japanese manufacturer uses glycol based fluids and recommends regular fluid changes. So, unless you are in the habit of spilling brake fluid, I would stick with what the manufacturer recommends.

Here is a link that discusses this in detail:http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

 

DOT 5 and DOT 5.1 are different. As Super said, DOT 5 won't absorb moisture, which causes lots of problems. It's for RACE CARS !!

Now why can't I find any DOT 5.1 Synthetic anymore ??

 

I wouldn't recommend it either. Good old DOT3 works just fine, and it's cheap enough that keeping it fresh isn't a problem. Proper shop etiquette prevents fluid spills.

 

I wrote these notes after doing some research via some link in chacal's links,

<SNIP>
Brake Fluid
D.O.T 5 is silicone based (Non-lubricating)
D.O.T 1,2,3,4 and 5.1 are glycol based (lubricating)

The higher the D.O.T rating the better it handles moisture penetration into the system, better dispersion etc.
More moisture in the brake fluid makes it more compressible.
</SNIP>

Made sense when I wrote it... steer clear of DOT 5 unless manufacturer recommended but go as high a DOT rating otherwise(except 5 of course) that you can find was my final conclusion.

 

True. The moisture just ends up sitting in the calipers. Can't get it out by normal flushing because it lays on the bottom rather than being picked up by the fluid.

DOT 5 does suspend small air bubbles though. So if it gets agitated you'll be forever bleeding your brakes.

The military likes DOT5 because it performs well over a very large temperature range. Custom car builders like it because spills won't damage paint. People that just want to stop without maintenance headaches use the glycol based fluids (DOT 3, 4, 5.1).

 

All information sounds reasonable. We in the lift truck industry use a lot of DOT 5. I thought it would be OK after several industrial equipment OEM reps said the it was compatible. Time to rethink!! Thanks for the info.

 

Most lift trucks don't spend a whole lot of time outside, or on the highway, or in the rain; and I'll bet they don't often have to stop from high speed either.

I would actually be even more concerned with using it in a car; when you said "all your vehicles" you didn't mean your 4-wheeled ones too?

Another good example of the benefits of discussing ideas like these.

 

So far I've only changed the Maxim. It's only one not still under warranty other than the Mustang. My intention was to switch as the warranty expires. I didn't want to give the OEM any reason to deny warranty. After reading the link Super supplied, I can see that the maintenance issues using DOT 5 will be more than the few minor benefits it MIGHT provide and aren't worth it. The Maxim will be flushed and returned to DOT 3/4 in the next day or so.

 

Our '08, 4000+lb Tribeca with 3500lb tow rating uses ONLY DOT 3, with a 30 month replacement interval or, to quote the maintenance guide, 15 months if "used in high humidity areas or in mountainous areas".

I seriously doubt most of us will ever get our XJ's brakes hot enough to boil the fluid, the big enemy is moisture. My bike sits in a frozen garage for 6 months a year, so for the small amount of time it takes to flush the fluid and and moisture every spring, DOT 3/4 is used.

Its a painless operation with the fancy high tech bleeding can I made:

http://xjbikes.com/Forums/viewtopic/t=31200.html

Dave

83 900

 

Switched back to DOT 3. On a previous post about front brake locking when reversing the bike, I indicated that changing to DOT 5 solved my issue. It came back. When I switched back to DOT 3, I replaced the calliper seals and cleaned some corrosion out of the grooves. Problem completely gone now.