Brake fluid question

[cmar157]

This may be a stupid question but I need to add some brake fluid and I bought the Prestone and it says it is synthetic. Is this OK to use to add to the existing fluid or should I go get the BRP brand?

Thanks

[Chupaca]

don't add synthetic fluid. You can only use synthetic if you drain, flush and replace seals in the whole system. You can use Dot 3 or 4 but not 5/synthetic...

[Lagaffe]

Spyders needs DOT 4 brake fluid.

[msj4848]

Dot 3, 4, and 5.1 are all glycol based, and can be mixed. Your Spyder uses dot 4, so using dot 3 would be a downgrade in the boiling point, and isn't a good idea. Fluids marked "dot3/dot4" are acceptable. Just don't use dot 5, which is silicone based, extra bad idea.
Regarding "synthetic"--glycol based (3, 4, and 5.1) are all synthetic. It's just a marketing gimmick to make people think it's better.

[jerpinoy]

Dot 3, 4, and 5.1 are all glycol based, and can be mixed. Your Spyder uses dot 4, so using dot 3 would be a downgrade in the boiling point, and isn't a good idea. Fluids marked "dot3/dot4" are acceptable. Just don't use dot 5, which is silicone based, extra bad idea.
Regarding "synthetic"--glycol based (3, 4, and 5.1) are all synthetic. It's just a marketing gimmick to make people think it's better.

Thanks for all these technical info.

[KX5062]

don't add synthetic fluid. You can only use synthetic if you drain, flush and replace seals in the whole system. You can use Dot 3 or 4 but not 5/synthetic...

Sorry, but that's not correct, that's the old stuff. The newest formulas can be freely mixed together without a problem. The only difference between DOT3 and 4 is the static boiling point, with the DOT4 being the higher boiling point. MSJ's summary is right on the money, however, I might take issue with the marketing gimmick comment, but otherwise well put.

[KX5062]

All of this got me thinking/wondering about brake fluid, since I'm not really up to speed on it, just shade tree knowledge. So, I started reading. The market gimmick comment by msj4848 was right on the money.

Apparently, there is no difference between regular brake fluid and so-called synthetic brake fluids, except for cost. DOT3,4, and 5.1 are all gycol based formulas. (DOT5 is silicon based and not compatable.) There were some unsubstantiated claims that DOT3 fluid handle water absorption better than DOT4 fluid, but I didn't find any science to back up those claims.

From my reading it seems the 2 best/most highly regarded brake fluids are "ATE Type 200 #706202" DOT4 rated and Castrol LMA. Motul is well thought of as well, but appears to absorb moisture quickly and needs to be replaced annually.

[msj4848]

MSJ's summary is right on the money, however, I might take issue with the marketing gimmick comment, but otherwise well put.

The fact that dot3, 4, and 5.1 fluids are all glycol based translates into the fact that they are all synthetic fluids. So when a manufacturer "takes advantage" of that fact and plasters a big bold "SYNTHETIC" label on their product to justify a higher price or to make you think it's better than a bottle next to it that isn't labeled so, kinda sounds like a gimmick to me, imho.