Brake Fluid

alexgee · Post by **alexgee** » Wed Jan 09, 2008 8:53 am

what is the DOT rating show on brake fluid? Is it purely the boiling points are higher with the higher DOT rating?

Rich H · Post by **Rich H** » Wed Jan 09, 2008 10:16 am

DOT is the standard the fluid is made to, DOT 4 being most common, but DOT 5 is silicon based for some citreons and other random cars it is incompatible with most brake systems. DOT 5.1 is ok though for some reason.

Dunno the logic behind it all though. I thought DOT was Department of Transport so I assume they standardised it at some point.

steve_weegie · Post by **steve_weegie** » Wed Jan 09, 2008 10:32 am

All DOT 4 fluids are glycol based and absorb water, reducing their boiling point and thus need replaced every wee while. The standard is quite old, and modern DOT 4 fluids come in all kinds of variety's and operating temperatures.

As rich says DOT5 is completely different to DOT4 and incompatable with DOT 4 systems

DOT 5.1 is compatable with DOT4 systems, but is based on diferent chemical technology. I believe DOT 5.1 is significantly thinner than a comparable DOT4 fluid and is required for many ABS systems.

Dont you just love logical standards

Rich H · Post by **Rich H** » Wed Jan 09, 2008 10:50 am

I think that the DOT 5.1 absorbs water quicker than DOT 4 so degrades quicker form memeory, could be an old wives tale though.

Best stuff I reckon would be the Racing BLue stuff, you can tell when the old stuff is flushed out!

steve_weegie · Post by **steve_weegie** » Wed Jan 09, 2008 11:13 am

RICHARDHUMBLE wrote:I think that the DOT 5.1 absorbs water quicker than DOT 4 so degrades quicker form memeory, could be an old wives tale though.

Best stuff I reckon would be the Racing BLue stuff, you can tell when the old stuff is flushed out!

Now that's handy, i didnt realise the fluid was actually blue!!

Rich H · Post by **Rich H** » Wed Jan 09, 2008 11:14 am

Not used it yet (Never remember to order it when I need it, but I think Simon recommended it.

steve_weegie · Post by **steve_weegie** » Wed Jan 09, 2008 11:18 am

Mac was chatting to me about it at the weekend too, and reccomended it. I use ap 600 stuff at the moment and it looks like the two are pretty similar in performance. AP600 is not blue though so definatly lagging in the cool stakes

woody · Post by **woody** » Wed Jan 09, 2008 12:32 pm

Lotus recommend Castrol super Dot 4 as a minimum, just bought some to refil mine with. Castrol SRF is supposed to be good stuff for on the track.

Rich H · Post by **Rich H** » Wed Jan 09, 2008 12:41 pm

SRF is stupidly expensive...!!

BigD · Post by **BigD** » Wed Jan 09, 2008 10:22 pm

I use Motul RBF600 and it is awesome.

Does require a flush once a year though. Only really necessary if you are having issues with boiling the fluid/fade. Unfortunately my heavy metal car takes a bit of stopping.

Andy · Post by **Andy** » Wed Jan 09, 2008 11:44 pm

Dot5.1 is spongier which allows the ABS system to operate. It can give a slightly more mushy pedal than a good quality Dot4.

BigD wrote: use Motul RBF600 and it is awesome