Motul Dot 5.1 brake fluid track questions
 

Hello everyone,

I'm thinking about hitting the track for a HPDE this weekend in my Zl1. I've ran several of these in my old Mustang where I used to run Motul 600 fluid and Carbotech brake pads. I have recently moved from Chicago to the Detroit area and just got some interesting advice. A mechanic told me that switching from Dot 3 in my Z to Dot 5 synthetic could cause a host of problems. Mainly he was worried about the moisture that is already in the lines and the seals degrading. I never had this problem in my Mustang which was a DD and saw 4-6 HPDE's a year. Is this true? If I swap to Motul 600 will my seals start to fade due to the incompatibility of the fluids? If that is true is the Motul dot 5.1 suitable for track days? Also I would be getting a full brake flush when adding the new fluid but I guess I'm wondering if that's enough. Thanks in advance.

A few things:

Motul 600 is DOT 4. Perfectly fine to use.

Motul has a 5.1 fluid, also perfectly fine to use, but is not a high performance fluid like the 600 is, so you are better of with Motul 600 for track use.

The mechanic is right that DOT 5 fluid should not be used and mixed with DOT 3,4, and 5.1. The numbering scheme was a bad choice. 5 is a different animal than 5.1 and not compatible.

Motul 600 DOT is what I use....never had a problem

Thank you Z28LT1 and Kaboom for the fast response. I thought it was ok to use but he had me second guessing everything after that.

From what I understand you can use the DOT 5.1 but it absorbs moister faster so you have to change it more often. This was really designed for race team that swap their fluids out before and after every race.

Has anyone used that BG super DOT 4 stuff? A brake shop down the road from me uses this in one of their flush machines. Anyone had any issues on track days with it? It's rated at over 500 degrees but it's about 85 degrees less than the Motul 600.

There is nothing that inherently makes 5.1 absorb moisture faster and being 5.1 doesn't necessarily mean it needs to be change more often. It is usually made of similar components, and needs to have a higher wet and dry boiling point, as well as lower viscosity than DOT 4. The best DOT 4 fluids will exceed the Dot 5.1 boiling point requirements. Observationally, it seems that manufacturers need to sacrifice absorption resistance to achieve the higher boiling points, so something that meets the minimum 4 standards might need to be changed a little less than something meeting the minimum 5.1 standards. But this isn't always the case and the fluids we discuss aren't minimally meeting the specifications. Motul recommendations more frequent changes to their DOT 4 600 over their DOT 5.1 fluid. Valvoline has the same exact recommendation for their Dot 4 and Dot 5.1 fluids as some examples. It really is more fluid than regulation dependent.

Never used the stuff. The super dot 4 or dot 4 plus fluids in theory should meet 5.1 standards. that gives you the 500 degrees dry boiling ping and 356 wet. The Motul 600 wet is 421 degrees, which is why it is so popular. If the BG stuff minimally meets Dot 5.1 specs, it slots below things like the ATE blue/Type 200 stuff. Based upon the numbers alone and no actual experience, I would think for advance drivers, this probably isn't enough, but for beginner drivers it is a good upgrade from stock.

I went with motul 660

That would be incorrect. DOT 5 fluid DOES NOT absorb water, which is why it has to be replaced more often.

Also it's nearly impossible to change a system from DOT3/4 to DOT5. DOT 5 is silicone based, and does not play nicely with other fluids.

Kaboom mentioned 5.1, not 5. 5 does not absorb water and is sometimes used in places where a longer change interval is needed. 5.1 is just like 3 and 4 and absorbs water. Has the same boiling points as 5 but really should have been called 4.1 or something to avoid confusion.

bottom line...do not use DOT 5 fluids in our systems. Motul 600 & 660 are DOT 4 and totally compatible with stock fluid which is DOT 3. Flush the system with a power bleeder like the Motive unit and be confident the system is 100% high temp fluid and has no residual low temp factory fluid.

I like Castrol SRF. Expensive but worth it. I can run 18+ track days a year and just bleed it after each event. Flush at the end of the season.

The Motul RBF 660 has the highest dry and wet boiling point. If I was going to change the stock fluid, that is what I'd use.


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