View Full Version : Brake Fluid

03-12-2010, 08:58 PM
We've had a few discussions about fluids over the past several years, some with very good info.

But a new question has arisen. I've noticed a number of fluid manufacturer's, namely Valvoline, now sell a synthetic fluid for "DOT3&DOT4" use. Is this this new synthetic better than the old DOT4? To lump it together with DOT3 it must be as good or better, since 3&4 are quite a bit different, yes? What do you guys know?

03-12-2010, 09:05 PM
DOT4 is basically just a higher temp version of DOT3. The fluid is backwards compatible, which is why Valvoline markets it as such.

Adding DOT3 to DOT4 will slightly lower the boiling point, adding DOT4 to DOT3 will slightly raise it. Maximum temperature resistance is achieved with using only DOT4.

None of this applies to DOT5, it's a whole different composition and is not compatible with 3 or 4.

03-12-2010, 09:20 PM
Thanks Cris. I'm aware of that bit, but this question is aimed at synthetic vs non-synthetic. So far in my findings it seems that it goes like so- DOT3 SYN has a higher boiling point than DOT3 non-syn like closer to non-syn DOT4, while DOT4 syn has a higher boiling point than DOT4 non-syn and thus higher than the other two. Also, the synthetic bit does not mean it is silicone based like DOT5, it still uses a poly-glycol base. Sounds good to me, I just find that Valvoline labeling a bit confusing, because DOT3 syn and DOT4 syn are two different things. Kind of the way DOT5.1 was a tad confusing when introduced.

03-13-2010, 02:15 AM
Synthetic often means the actual chemical composition of the lubricating agent is the same, but the production method is different. Synthetic oils gain most of their benefit from their homogeneous nature -- think of it along the lines of a lot of tiny little balls. Balls of different sizes can settle together and sort of lock into place. However, uniformly sized balls cannot compact together. This is part of the reason why playgrounds now favour pea gravel, which can be sorted by maximum and minimum size, versus sand, which varies from dust to small pebbles and therefore can compact into a hard surface.

03-13-2010, 03:22 AM
IIRC correctly when they changed that label they also changed the fluid a little the boiling points are a little lower compared to the old Valvoline Synpower stuff. I still thinks it's the best off the shelf brake fluid, especially for the price. DOT 4 has always been backwards compatible with DOT3 so that 3/4 label is probably marketing since I bet many manuals call for DOT 3 fluid. ATE SuperBlue Racing fluid is also great but you'll most likely have to order that. It doesn't absorb moisture as quickly as other fluids and it's not too expensive, has a dry boiling point of 536F and 392F wet.

03-13-2010, 08:18 AM
I run Wilwood 570. I've not once had a problem with squishy brakes.

03-21-2010, 12:39 AM
I picked up some Wilwood 570 High Temp Dot3, which I thought was weird, I thought Dot4 and 5.1 were higher temp mineral based replacements for Dot3, then they had Dot4 synthetic, Dot5.1 synthetic, I was like WTF everything I know about brake fluid has gone out the door. Oh well, I bought enough bottles to do my truck and both Celica's.

What should I use for the clutch? I was thinking of changing the 90GTS fluid and see if that helps the engagement height, Im really hoping so.