I guess my only reason for using DOT4 is just habit, I go through a lot of brake fluid and 4 is acceptable for most everything I work on and own. The boiling temps aren't that different from 4 to 5.1 and I know none of my vehicles will get pushed to the limits, and the fluid is seldom older than a year in my bikes or sleds. So again it's just cost effective and convenient to keep one type in stock.

 

DOT 5.1 does not have a higher boiling point then quality DOT 4. Motul and Castrol have DOT 4 fluids with much higher boiling points both wet and dry then the recommended Motrex.

 

Forgive me - I thought we were talking about standards, and not specific instances of fluids that happen to conform to a particular standard. I could certainly see that not all DOT 4 fluids are created equal. So, to compare apples to apples, I went to Motul's site (this is a cut-and-paste):

MOTUL DOT 4 LV high wet boiling point (172°C / 342°F) is superior to conventional fluids DOT 3 (140°C / 284°F mini) and conventional DOT 4 (155°C / 311°F mini) and therefore enables longer product lifetime.

MOTUL DOT 5.1 high wet boiling point (185°C / 365°F) is superior than the requirements of the standards DOT 3 (140°C mini / 284°F mini), DOT 4 (155°C mini / 311°F mini) and DOT 5.1 (180°C mini / 356°F mini), and therefore enables longer use of this product.

Which brings me back to the original question, rephrased in light of this exchange: why would one run DOT 4 when just about every brand you would care to mention has a DOT 5.1 in their line that is superior in terms of the key metric? Perhaps the cost is very different?

 

5.1 is not silicone .
Totally agree that using factory specs the smart and safe way to go. In our case, factory recommends DOT4 OR DOT 5.1, if I was really pushing the bike to IT'S limits I would renew the brake fluid every year with 5.1, seeing that I'm just a mere mortal that never track rides, 4 is all the I will ever need. DOT4 used in all my motorcycles, cars, trucks and snowmobiles. Never experienced brake fade in any of them.

 

Well, I looked back, and it WAS DOT 5 I was referring to as opposed to 5.1. Not sure if 5.1 has silicone, but still best to stick with the factory-recommended stuff.

 

It's not all on you, the classifications aren't as clear as they should be, and probably won't be fixed till people start loosing their brakes and people are hurt or killed because someone mistakenly puts the wrong fluid in their brake master cyl.

 

Right. Brain fart.

 

Using other than the recommended brake fluid is risky. Seals may not be compatible, among other possible problems. If the manufacturer says it's ok, then use it if you like.

 

I am curious: why would people use 4 over 5.1, when the latter is superior in the most important metric: boiling point?

 

Crystalized in the system?! You mean the silicone stuff? Where did you learn about that? I have never heard this before.

 

Takes a long time. One would think since it doesn't suck water, it could occupy a closed system forever. If you've ever owned a really old motorcycle since it was practically new, you find out what lasts a long time and what goes to hell from disuse.

 

Nothing but .4. I think .5.1 was formulated after everyone who used .5 found out it crystalized in the system.

 

Okay, good to know. Thank you, I really appreciate it!

 

yup 4

 

DOT 5.1 has a higher boiling point than DOT 4. Apart from that...

 

DOT 4 here...in all my bikes, and my cars.

 

Yes, I do use DOT 4 Motul for my R. No issues as far as I can tell.