[Healeys] Brake Fluid

Mon Oct 31 17:56:19 MDT 2022

I made myself some notes which I later submitted to our local AH mag. Here’s the gist of them. May have posted this before….

1.	“All brake fluid is “synthetic”…it’s not a “natural” product.
2.	Most synthetic fluids are NOT silicone. They are polyethylene glycol ether based.
3.	DOT 3 & 4, which can be mixed, are not silicone. They are glycol.
4.	DOT 5, which cannot be mixed with 3 or 4, is silicone. Can’t be mixed with anything!
5.	DOT 5.1 is glycol based and cannot be mixed with DOT 5.
6.	DOT 5.1 can be mixed with DOT 3 or 4, as both are glycol based.

The word “synthetic” began to appear when manufacturers worked out that it made regular brake fluid sound more special ie they could charge us more money for the same old stuff.

DOT stands for Dept. Of Transport and relates to the fluids’ boiling points. If a car brakes at high speed, the brakes get hot. Some heat is carried away from the brakes by the brake fluid. Bad news if the fluid boils! The faster you’re going, the higher DOT you need. Higher DOT numbers indicate higher boiling points for “Dry” fluid (has not absorbed any water) and “Wet” fluids (has absorbed water). ie, the wetter it is, the more problematic it becomes. Mixing 3 with 4 lowers the boiling points and vice verca.”

Simon

From: Healeys <healeys-bounces at autox.team.net> On Behalf Of Mark Donaldson
Sent: 31 October 2022 22:06
To: 'Bob Spidell' <bspidell at comcast.net>; healeys at autox.team.net
Subject: Re: [Healeys] Brake Fluid

DOT5 and DOT 5.1 are NOT compatible.

I’ve have been using Bel-Ray DOT5 SBF in my BN2 and my tri-carb since 1992.

I’ve never had a problem.

Mark

Ardmore, NZ

From: Bob Spidell <bspidell at comcast.net <mailto:bspidell at comcast.net> > 
Sent: Monday, 31 October 2022 5:35 PM
To: healeys at autox.team.net <mailto:healeys at autox.team.net> 
Subject: Re: [Healeys] Brake Fluid

"... There is a newer Glycol Ester DOT5 ..."

I think you're referring to 'DoT5.1'  I also think it was deliberately named so as to confuse the issue.

On 10/30/2022 8:05 PM, Christopher Moog via Healeys wrote:

I've used both. Currently prefer DOT4.

Also everyone is speaking of DOT5 but there are now two different DOT5s. The first is the older silicone based DOT5. There is a newer Glycol Ester DOT5 that is compatible with DOT3 and DOT4. It has a lower viscosity than the DOT3 and DOT4 so it works better in some ABS systems. It also has a higher boiling point than DOT3 and DOT4. Don't see an advantage in Healeys.

On 10/30/2022 10:00 PM, Alan Seigrist wrote:

The best selling point for Dot 4 is you can mix any Dot 4 or even Dot 3 if you need to fill up.  As I understand it with Dot 5 you should be careful to always use the same brand to fill up if necessary.

Also, neither Dot 5 not Dot 4 is great for sitting a long time, Dot 4 absorbs water, Dot 5 will push any water down into the components.

Dot 4, if the car is not used regularly, needs to be flushed every couple of years.

On Mon, Oct 31, 2022 at 5:43 AM Michael MacLean <springer.mike51 at gmail.com <mailto:springer.mike51 at gmail.com> > wrote:

At this point in the restoration I have a completely rebuilt brake system with all new components and tubing.  Now is the time to make the decision to use DOT 4 or Silicone.  What's the consensus, if there is one?

Mike MacLean

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