DOT 5.1 Fluid Instead of DOT 4

[ARAMP1]

Kind of surprised I haven't been able to find much info on this on the forum...

My GT350 is the only vehicle I own that calls for DOT 4 brake fluid. Everything else is DOT 5.1, so I have a bunch of it on the shelf. Is there any down side to using DOT 5.1 instead of DOT 4? It's just a daily driver, not tracked GT350.

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[Cory S]

DOT 5.1 has very wide applicability and can be used with confidence in any brake system where the use of glycol ether fluid is specified. This includes the latest generation full electric and electric hybrid vehicles where low conductivity is essential, as well as high performance European vehicles. It is fully compatible with and can replace or top up systems using DOT 4 and DOT 3 fluids.

 

[ARAMP1]

DOT 5.1 has very wide applicability and can be used with confidence in any brake system where the use of glycol ether fluid is specified. This includes the latest generation full electric and electric hybrid vehicles where low conductivity is essential, as well as high performance European vehicles. It is fully compatible with and can replace or top up systems using DOT 4 and DOT 3 fluids.

I've read that. Thanks.

 

[ARAMP1]

Well doing a little bit of google-fu, I've found that the DOT 5.1 probably isn't the way to go, even on a street car.

Motul DOT 5.1

Viscosity at 212°F - 2.1 mm²/s
Viscosity at -40° - 820.0 mm²/s
Dry boiling point - 522.0 °F
Wet boiling point - 365.0 °F

Motul 660

Viscosity at 212°F - 2.6 mm²/s
Viscosity at -40° - 1698.0 mm²/s
Dry boiling point - 617.0 °F
Wet boiling point - 401.0 °F

Castrol SRF

Viscosity at 212°F - 3.5 mm²/s
Viscosity at -40° - 1300 mm²/s
Dry boiling point - 608 °F
Wet boiling point - 518 °F

EDIT TO ADD:

Motorcraft DOT 4 LV (PM-20)

Viscosity at 212°F - ? mm²/s
Viscosity at -40° - ? mm²/s
Dry boiling point - 509 °F
Wet boiling point - 338 °F

 

[Jstang23]

@ARAMP1 I'm sure dot 5.1 would work fine, but keep in mind your system was engineered to run dot 4 LV. Which is very different from 5.1. I've always ran the motorcraft fluid unless I was tracking it which I put rbf660 in. In addition, the stock brake fluid is 338 wet and 509 dry. So, pretty similar to 5.1 performance.

 

[ARAMP1]

I also came across a blurb that said the 5.1 was more hydroscopic than the DOT 4, but nothing official.

 

[Jstang23]

I also came across a blurb that said the 5.1 was more hydroscopic than the DOT 4, but nothing official.

I'd honestly stick to the dot 4 lv. I got a pack of 5 for about 60 bucks from a ford dealer, it'll be the last time I buy brake fluid for the car. When I run the RBF 660 I flush it out after the track day as the ABS system won't function properly at cold temperatures without the LV fluid.

 

[Garfy]

I also came across a blurb that said the 5.1 was more hydroscopic than the DOT 4, but nothing official.

That's what I read somewhere also, which means you'd have to replace the fluid more frequently than DOT 4. I used to replace my fluid every 2 years before but now I live in a drier climate so will just continue to use my moisture meter and my test strips to determine when to flush the fluid out.

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