Synthetic and Non-synthetic Dot 4

Bob R · Oct 27, 2013

I went to the parts store to get some more Dot 4 brake fluid to finish the replacing job I started. They were out of the "regular" Dot 4, but they had some synthetic Dot 4. Can they be mixed?

Also, I noticed they had Dot 5 synthetic. It was quite a bit more expensive than the Dot 4. I didn't buy any and I wouldn't mix it with the Dot 4, but I was wondering if it is safe to use in the bike next time. I know the manual says to only use Dot 4, but I had never heard of Dot 5. Any advantages or disadvantages to using it instead of Dot 4?

White_Wing04 · Oct 27, 2013

Check this out http://www.advancepetro.com/differentbrakefluid.htm

Bob R said:
I went to the parts store to get some more Dot 4 brake fluid to finish the replacing job I started. They were out of the "regular" Dot 4, but they had some synthetic Dot 4. Can they be mixed?

Also, I noticed they had Dot 5 synthetic. It was quite a bit more expensive than the Dot 4. I didn't buy any and I wouldn't mix it with the Dot 4, but I was wondering if it is safe to use in the bike next time. I know the manual says to only use Dot 4, but I had never heard of Dot 5. Any advantages or disadvantages to using it instead of Dot 4?

White_Wing04 · Oct 27, 2013

Looks like DOT3,DOT4 and DOT 5.1 are ALL Synthetic. DOT 5 is Silicone and it doesn't play well with the others.

Bob R said:
I went to the parts store to get some more Dot 4 brake fluid to finish the replacing job I started. They were out of the "regular" Dot 4, but they had some synthetic Dot 4. Can they be mixed?

Also, I noticed they had Dot 5 synthetic. It was quite a bit more expensive than the Dot 4. I didn't buy any and I wouldn't mix it with the Dot 4, but I was wondering if it is safe to use in the bike next time. I know the manual says to only use Dot 4, but I had never heard of Dot 5. Any advantages or disadvantages to using it instead of Dot 4?

Igneouss · Oct 27, 2013

The simple explanation for brake fluids:
Higher DOT # equals higher boiling temp. Do not use a lower number than specified for your vehicle.
With one exception they can all be mixed.
DOT 5 is a legacy product intended for collector cars and a few other applications. It stands by itself and cannot be mixed with other brake fluids.

MIXING: Don't mix in lower than specified #s.. Brake systems get hot. And the times they get really hot are exactly the times when failure due to boiling will kill you.

Cheers!

GoldWingrGreg · Oct 27, 2013

The Service Manual warns against mixing "types." In a prior post someone said that ment don't mix Dot 4 with Dot 5. I take it to mean that, as well as don't mix non-synthetic with synthetic.

s.whisker · Oct 28, 2013

Without knowing what material the elastomers might be made of I would stick with what is recommended.

Elastomer compatibility chart
http://www.hitechseals.com/chemical-compatibility.asp?chemical_id=1628

http://www.kmcoinc.com/Dot 4 MSDS rev 5 (12-06-12).pdf

chuck_b24 · Oct 28, 2013

Back when I was young & dumb (old & dumb now) I used dot 5 in a few bikes I worked on . I ended up changing ALL of them back to dot 4!!! Dot 5 made the brakes "notchy" feeling ( not smooth at the lever????)

I have NEVER had problems mixing synthetic with non synthetic ..

The next time I change fluid I will try 5.1

White_Wing04 · Oct 28, 2013

That's because they are all synthetic.. lol

chuck_b24 said:
Back when I was young & dumb (old & dumb now) I used dot 5 in a few bikes I worked on . I ended up changing ALL of them back to dot 4!!! Dot 5 made the brakes "notchy" feeling ( not smooth at the lever????)

I have NEVER had problems mixing synthetic with non synthetic ..

The next time I change fluid I will try 5.1

Bob R · Oct 28, 2013

So as I understand it, all brake fluid now is synthetic, even though it doesn't say that on the label on one of the containers, so it's ok to mix them as long as they are both Dot 4. Right?

crabbywinger · Oct 28, 2013

Bob R said:
So as I understand it, all brake fluid now is synthetic, even though it doesn't say that on the label on one of the containers, so it's ok to mix them as long as they are both Dot 4. Right?

YES

Ride Safely

Crabby Bob

Igneouss · Oct 28, 2013

Wow. Some people are really over thinking this...

I'll say it again: The DOT # relates to boiling point. Higher # equals higher boiling point.

You can mix any of them accept DOT 5. DOT 5 is unique and specialized for antique vehicles. Ignore DOT 5. Don't buy it.

All the others can be mixed any way you want. Just be aware of your vehicles' spec so you do not use (or mix) a # lower than specified. If you do you risk boiling and brake failure as a result.

Synthetic and Non-synthetic Dot 4

Bob R

White_Wing04

White_Wing04

Igneouss

GoldWingrGreg

s.whisker

chuck_b24

White_Wing04

Bob R

crabbywinger

Igneouss

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