Super DOT4 explained: ISO 4925 class 6

Here is some information found while researching brake fluid, in particular the difference between ATE 200 and ATE SL6. This of course led down the rabbit hole as usual.

It seems that the "Super DOT4" appellation that has been flogged many times actually has a basis. That basis can be found in ISO 4925 class 6. That is a international brake fluid specification whereas DOT4 is primarily a North American specification based on FMVSS.

ISO 4925 class 6 addresses brake fluid with low temperature viscosity requirements for ABS and traction control systems. It also addresses chemical compatibility with two specific newer seal materials. All contemporary Jaguars have ABS systems.

The viscosity of such a brake fluid at -40C is in the range of 750 cST whereas typical DOT4 is in the range of 1500 cST.

The requirement for low viscosity is aimed at ABS cycle response time. In other words, how fast the system can apply and release the caliper piston when ABS or traction control is activated.

Shell claims "several times faster" whereas another vendor claims "30 percent faster".

So why Super DOT4?

Because there was no matching DOTx specification that matched ISO 4925 Class 6. So, "let's just call it Super DOT4" is a best guess at the reason.

The result is that the original fill and specified replacement fill are in fact not generic DOT4. The "real" brake fluid can be called DOT4 because it fits the FMVSS standard, but the *real* brake fluid has superior operating characteristics tailored to the ABS system.

Therefore, while someone can pour generic DOT4 into their system and claim that there is no such standard as "Super" DOT4, they have in fact downgraded from the original intent, and downgraded their braking system.

In addition to the above mentioned Shell ESL Super DOT4, there is ATE SL6, as well as similar class brake fluids from Pentosin and Motul. GM and Ford branded fluids are also a possibility. (researching the specs on those is left to the reader )

The benefits of using the above class of brake fluids would be:
- ABS reaction time, one writer mentioned "smoother ABS operation"
- better brake pad retraction resulting in longer brake pad life and better gas mileage (and probably less brake dust for those who care)

The ATE SL6 is actually a few dollars less than the ATE 200.

The easiest places to find suitable brake fluid are ... VW performance shops because VW also refers to "Super DOT4". The Pentosin that a lot of shops use is half the price of the ATE SL6.

And for those who like pictures ... see the attachment for a graphical response time comparison

The ATE SL.6 DOT 4 fluid did make a noticeable change in the action of the ABS. Before, I'd take the tires all the way to lockup and I'd get one release of the brakes to get the tires rolling again, then the ABS wouldn't catch any more lockup after that. I'd feel one snap on the brake pedal, and that was it. Today I took it out at the same speeds on the same stretch of road with the tires warmed up just like before, and the ABS would give me a nice little tap, tap, tap on the brake pedal as it intervened in a more gentle and progressive way. I tore up and down the stretch of road testing this in 60 mph to 20 mph stops (didn't really want to flat spot a tire) and found that when the ABS finally did kick in, it was more subtle than before.