Brake fluid-again! - Rudedog
I am sorry that this thread has been covered before.
I am about to change the fluid on my Golf 4 TDI, will I see any difference in performance in up grading to DOT 5.1 from DOT 4. Also how will this effect the use of the clutch as the fluid is used for both brake & clutch.
Brake fluid-again! - Rudedog
I forgot to say that I was confused because the Halfords DOT 5.1 is recommened for use in cars with ABS, does this mean that DOT 4 is unsuitable? or of a lesser spec.
Brake fluid-again! - Aprilia
Brake fluids are yet another area where a lot of confusion has crept in over recent years because of the proliferation of new fluids available. Currently you can buy DOT 3, DOT 4, DOT 5 and DOT 5.1. DOT 3, 4 and 5.1 are glycol-based fluids. DOT 5 (NOT TO BE CONFUSED WITH DOT 5.1) is a silicone-based fluid.

Bascially, DOT 3 has been superceded by DOT 4 and unless you are motoring on a budget then DOT 3 is probably best avoided.

DOT 4 has superior properties to DOT 3, in particular a higher boiling point, and is a good general purpose brake fluid.

DOT 5.1 is a lighter viscosity version of DOT 4 and is particularly suited to ABS sytems where fluid must be pumped and pass through small valves. Its boiling point is not necessarily higher than that of DOT 4. I believe it is also less agressive towards paintwork, so if you spill some on the bodywork its not such a disaster!

DOT 5 is a silicone-based fluid. There are many 'issues' with it; in particular you may end up with a 'spongy' pedal due to the greater compressibility of silicone vs. glycol. Really, DOT 5 is only for special applications (e.g. classic cars, racing, etc.) and should be avoided by the everyday motorist.

In summary, for a modern car DOT 4 or 5.1 will be fine - 5.1 just has the edge for ABS.
Brake fluid-again! - Aprilia
Forgot about the clutch.

You will not notice any difference in clutch operation.
Brake fluid-again! - Cyd
FMVSS116 requires the minimum dry boiling points to be:
DoT 4 230C
DoT 5.1 260C

Minimum wet boiling points are 155C & 180C resp
The max viscosities at -40 are 1800 & 900 mm2/s resp.

It's the lower viscosity in particular that makes DoT 5.1 more suitable for ABS, especially in colder climates.
Brake fluid-again! - Drew20
in terms of pence per mile between changes, there is no real cost to 5.1 Get the best you can find. Dot 5.1 is best for ABS though if you can't find it dot 4 will be fine

i think the dot 5 issue has been dealt with!!!
Brake fluid-again! - pmh
There is also a compatibility issue between brake system and

My Mk 96 Fiesta which was subject to a brake fluid related recall specifically says use DOT4 only, NOT SuperDOT4.

Can any body throw any further light on this?
pmh (was peter)
Brake fluid-again! - Cliff Pope
I recently found an unopened tin of the old Castrol Crimson. Not a Dot number in sight!
Brake fluid-again! - none
Cliff, whatever you do don't mix it with the amber fluid. Curdling will occur.
Brake fluid-again! - Aprilia
I cannot imagine why there would be a problem with Super DOT 4. I know lots of cars left the factory with it as the OE fluid. Its a diethylene glycol fluid, like DOT4, but formulated to have a somewhat higher boiling point.
Brake fluid-again! - Rudedog
OK I am going to try DOT 5.1, but it would interesting to know what is fitted as OE to Ferraris etc., if it's good enough for them ........
Brake fluid-again! - pmh

I cannot understand why Ford went to the trouble of issuing a self adhesive warning label to warn against mixing with Super DOT4. I have still got the label (and have checked it), so it is not a figment of my failing imagination!

pmh (was peter)


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