Dot 5.1

[NA Drifter]

well, I'll not going to use Dot 5.1 if I'm you. I'll stay with something like Dot 4.
As DOT 5.1 are mainly for RACING use. So they not as great for normal use since you won't out runs ur brake most the time.
I got this advice from a friend and he learn it from Drift King!(thru video)
I think one of the reason is DOT5.1 absorb more moisture than DOT4 so u need to bleed then time to time or change the whole fluid on the car. Race car thend to change their whole break fluids before every race.
Also since u using good pads, you should be fine at the track. As long as ur brakes have enough air cooling them down.

I hardly get brake fade on the track... as long as I don't do grip racing I did time attack on my TE71 and I go brake fade in 3rd lap at Manfeild... Metal King didn't help much! But if I do drifting.. brake will not fade at all.. .. cos i don't use them much.

[Perky]

Dimmy and NA Drifter,

you are still confusing DOT 5.1 and DOT 5.

DOT 5.1 is not a racing fluid (many would argue that DOT 5 isn't either but that's a different issue).

DOT 5.1 is simply the next highest rated glycol fluid from DOT 4.

DOT 5 is a silicone fluid and has many characteristics different from the glycol fluids DOT 3, DOT 4 and DOT 5.1.

DOT 5.1 does not absorb more moisture than DOT 4. No fluid can absorb more moisture than enters the system through the seals etc. and one of the benefits of glycol fluids is that they can absorb this rather than letting it boil in the brake lines. The 'wet boiling point' of brake fluid, is the temperature at which the fluid will boil once it has absorbed some water. It is lower than the dry boiling point but much higher than the boiling point of the water.

DOT 5 -- the silicone fluid -- does not absorb water but has a high boiling point so is suitable for racing, where the fluid is changed frequently to prevent moisture build-up. It can also be good for museum cars where a hygroscopic fluid might make brake lines more likely to rust. Supposedly the US military also uses silicone fluid in military vehicles. As has been noted, it is reputed to be more compressible than glycol fluid, which affects brake feel.

Hardly anyone recommends silicone fluid (DOT 5) for road cars. There are many reasons not to use it. It does not mix with glycol fluids but, as far as I know it does not react with them either. However, silicone is reputed to damage the seals in brake systems that have previously used glycol so changing over is a big deal. Furthermore, since mechanics would never guess you use silicone, it may be difficult to avoid contamination. It is also less widely available and is not suitable for ABS.

DOT 5.1 -- the glycol fluid -- is compatible with DOT 4 but, since it is likely to be better, there is little reason to change back. DOT 4, and particularly Super DOT 4 are presumably as good as anyone needs for a road car. DOT 5.1 has better (minimum) wet and dry boiling points and is recommended for ABS equipped cars.

The only specific reasons I can think of not to use DOT 5.1 are:

1) It is a little more expensive and harder to find. I use the MOTUL brand but it is possible that Castrol's Super DOT 4 is actually a 5.1 -- neither the bottle nor their web site state its boiling points.

2)If you can afford racing fluids, with extremely high dry boiling points, most of these are rated DOT 4. (Note that high wet boiling points are more important for a road car that is not having its fluid changed frequently.)

5)DOT 5.1 is claimed to be slightly thinner than DOT 4 -- hence its suitability for ABS. This means that it may be more likely to leak from old brake seals. I suspect that if DOT 5.1 will leak out then the seals should be replaced anyway but, who knows? -- maybe this is a consideration.

In short, yes it is confusing but DOT 5.1 is NOT silicone fluid and has no special requirements. It is merely a better DOT 4.

[NA Drifter]

yeh i think i made confusion here... cos thought of DOT 5 or more are the same..
good that u clear it up. I normaly top up brake fluid with water when it read low... cos they are fuild anyway just kidding

[Erelyes]

Excellent post perky, cleared everything up very well.
+1 vote for stickying that post hehehe