brake fluid : DOT 4 vs DOT 3

[nsx1164]

I was chatting with some of the service techs at my local Acura dealer, and we talked about some recent clutch/brake service I had experienced.

They mentioned that Acura/Honda recommends DOT 3 fluid over DOT 4. Most high-temp fluid preferred by track guys is DOT 4 (Motul, ATE SuperBlue, Castrol SRF, AP Racing, etc). Seems they had noticed an increased incidence of hydraulic system failures (typically the master cylinder circuit, or the seals) with DOT 4, and recommend DOT 3.

Having said that, they (techs) think that my current fluid (MOTUL RBF600 - DOT 4) is superior to their stuff.

Has anyone heard of this preference for DOT 3 over DOT 4 brake fluid ??

[nsxtasy]

Originally posted by nsx1164:
They mentioned that Acura/Honda recommends DOT 3 fluid over DOT 4.

Not true. Look in your owner's manual and you'll see that it recommends either DOT 3 or DOT 4, with no recommendation of one over the other.

As far as I know, DOT 4 requirements are more stringent than DOT 3, so that any DOT 4 fluid also meets all DOT 3 specifications.

The only thing I can guess is that they were confusing DOT 4 with DOT 5 (silicone-based brake fluid), and that the failures were caused by using DOT 5 fluid. DOT 5 is NOT recommended by Acura/Honda.

[This message has been edited by nsxtasy (edited 12 August 2002).]

[DanO]

I would like to echo Ken’s remarks. Clearly, the mechanic was confusing DOT 4 with DOT 5. I compiled a table on the various wet/dry boiling points on DOT 3 – 5 fluid at: www.danoland.com/nsxgarage/definitions.html#Brake%20Fluid

DanO

[nsx1164]

When I first heard this, I asked them this -- do they really mean DOT 3/4 vs DOT 5 ??

NO.. They said DOT 3 is all they have, and all they have been told to use.

[Lud]

My only other theory would be that people who use DOT4 are more likely to be doing hard braking, and thus are more likely to have various brake problems. People who are not doing a lot of hard braking probably aren't going to bother upgrading to DOT4.

DOT3/DOT4 are both fine for the NSX. DOT3 does not provide any kind of extra protection over DOT4.