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james_ly

Why do Toyota use DOT 3 brake fluid?

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Noticed on the cap, it said DOT 3 only. I assume there’s no harm in using 4 or 5.1... but wondering whether to stick with Toyota stuff. 

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For daily driving in most cases (how many do downhill driving in mountains on regular basis and when do so, don't use engine braking?) even low boiling temp fluids should do. For track use, even "generic 5.1" won't be sufficient.

Dot 3 4 5 5.1 .. is not exactly clear cut the higher number the better, but each of them is more about chemistry for base and additives (eg. anti corrosion, anti foaming and alikes) used (though Dot testing standards have also minimum temps listed, but not that high as best fluids out there) and what brake system is compatible with/not harm in them. For track use one still should go after brake fluid with higher temps then what those generic standards spec, for example pmu g-four 335, endless rf650, castrol srf, brembo htc 64t, of for budget minded motul rbf 600/660. (though worth noting that higher boiling temp brake fluids are also more hygroscopic, so worth changing out more often, as it will degrade the more it absorbs moisture).

All you need to now, that all dot 3, 4, 5.1 brake fluids are compatible with each other and with brake systems specced for one of them.

Only thing you should care for - to not put in dot 5, that is silicone fluid, unlike polyethylene glycol based ones above.

Dry/wet temps of Dot 5.1 of 270/190C are higher then Dot 3 205/140, but if you compare with:

pmu_gfour335_chart.jpg

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I’ve tended to use 5.1 in the past on track and always been fine, I feel that the expensive fluids are a band aid for inadequate brakes/cooling. 

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22 minutes ago, james_ly said:

I’ve tended to use 5.1 in the past on track and always been fine, I feel that the expensive fluids are a band aid for inadequate brakes/cooling. 

Not really correct.

For optimum brakes you need top quality kit.

Dot three is probably all that's needed at the low performance/weight level of the gt86.

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james_ly: not bandaid if you want to get max out of brakes capabilities. For example, BBK would be non-MOT-street legal option here in LV, so rIght (for use) pads&fluid are must have to get most out of stockers. Though if one tracks his, i'd prefer to eliminate any possible bottleneck, so would use good fluid even with BBK.

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