[Dallastheologian]

I was wondering if I am supposed to use DOT 3 or DOT 4 brake fluid for my 2011 B5. It seems low so I want to top it off, but the manual just says DOT 3 or DOT 4 as specified.

[Ducati Scotty]

Either is fine.  You can even use DOT 5.1 which is NOT DOT 5.  DOT 5 is silicone based and incompatible with the others.

The main difference is boiling point, higher with each higher number.  This is important in race machines where brakes get hot enough to boil the fluid, not so Important for a Bullet

Scott

[Andy]

Okay, now I'm curious.

I have read, and have been told, that one should NEVER, EVER mix DOT ratings.  I forget why, but it's something to do with positrons and negatrons and universe-consuming time paradoxes.  There might have been space monkeys.

So when I saw in the owner's manual "DOT 3 or 4", I immediately asked my dealer, "What's in it?"  He didn't know. 

But *I* would like to know.  It's not f&^%%ing either/or.  It's one or the other, dammit!

[Ice]

DOT 4 is silicone based and as such does not hold moisture in suspension as DOT 3 does.

DOT 4 does have a higher boiling point than DOT 3

DOT 3 and 4 do not play well together and gelling is likely to occur if the two are mixed.

Flushing of the brake system is required when switching from one type to the other.

[Andy]

Yeah, but what the hell is in there now, and how do I find out?

[Ducati Scotty]

DOT 4 is silicone based and as such does not hold moisture in suspension as DOT 3 does.

DOT 4 does have a higher boiling point than DOT 3

DOT 3 and 4 do not play well together and gelling is likely to occur if the two are mixed.

Flushing of the brake system is required when switching from one type to the other.

Ice, it's 5 that's silicone based:
http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html
"So now we have D.O.T. 3, 4, 5, and 5.1, with all but the 5 designation being glycol, while the 5 is silicone. "

In addition to flushing when changing types, you should disassemble the system, remove all rubber seals and soak them in alcohol to get rid of any traces of the old fluid.  Even so, the seals may not be compatible with the different type of fluid and may deteriorate.

As far as mixing compatible types, I don' know if there's a problem with that.  Usually I don't top off, since it's only a few dollars a bottle and you're supposed to use a freshly opened bottle, and it's only a few dollars, I just flush the system while I'm at it.  So I guess I'm never really mixing.

Scott

[greggers]

So when I saw in the owner's manual "DOT 3 or 4", I immediately asked my dealer, "What's in it?"  He didn't know. 

Er, wouldn't he have been the one to fill it on delivery?

[Desi Bike]

Filled by the fine folks in Chennai on the line.

[greggers]

Huh interesting I guess I assumed all fluids would be added by the dealer. Saves a little weight and removes some potentially dangerous materials from the shipping equation

[Arizoni]

DOT 3 and DOT 4 are totally compatible with one another as far as their ability to mix and to work with the same seal materials without causing harm.

There is no potential problem with using or mixing DOT 4 in a system designed for DOT 3 however there are some braking systems which are designed for DOT 4 which might have a problem if someone put DOT 3 into it.

DOT 3 when new has a boiling point of 401*F while DOT 4 when new has a boiling point of 446*F.

Some of the newer cars use their brakes to stop wheel spin and to enhance the cars control-ability and many of these cars need the higher temperature DOT 4 because of the extra "workout" their braking systems might get when the cars computer starts applying one or more brakes while the driver is doing some "spirited driving".  In these cars mixing some DOT 3 fluid with their DOT 4 fluid will lower the boiling point of the fluid and it could cause a problem.

The Royal Enfield on the other has no real need for the extra temperature capability of DOT 4 but because there is no harm done by mixing the two brake fluids the book says you can use either one (or both mixed together).

[Andy]

The Royal Enfield on the other has no real need for the extra temperature capability of DOT 4 but because there is no harm done by mixing the two brake fluids the book says you can use either one (or both mixed together).

No time paradox or ravenous space monkeys will ensue?  Cuz if the universe ends, I'm blaming you...

[Arizoni]

No time paradox or ravenous space monkeys will ensue.

There may be a shift in the vortex  in your commode though.

Because of this, it is not advisable to leave any necessary bits within a close proximity of the operating medium.

[motomataya]

Just use DOT 4. If you have DOT 3 it will be fine. Never Never switch to DOT 5 in a system designed for DOT 4. The rubber parts may or may not be compatible.

[Arizoni]

"Never Never switch to DOT 5 in a system designed for DOT 4."
-------
I agree. 
So different is the DOT 5 (notice there is no decimal) that if I would have had anything to say about it when they came up with DOT 5.1 it would have been called DOT 6.
DOT 5.1 is similar to the DOT 3 and 4 but it is totally different from DOT 5 and relying on one crummy decimal point to distinguish it is IMO dumb.

It's best to just avoid the whole #5 series and be safe with an Enfield.

[singhg5]

The Service Manual shows a picture of KBX (perhaps an Indian brand) brake fluid DOT3 in the hand of RE worker, pouring into the master cyliner. DOT3 is most commonly used in India.

We get export models in which some parts are different from bikes sold in local Indian market. Nontheless DOT3 or 4 will not make any real difference for RE. As Scott has pointed out, use a freshly opened bottle - it is not expensive. Just a reminder - the liquid can immediatey remove paint - protect all painted surfaces !