Silicone brake fluid

[Bluebottle]

When my wife bought her car, the chap who had built the kit said he always used silicne fluid for the brake and clutch.
Two reasons he gave were reduced corrosion of the copper pipes and less risk of damage to the painted surface under the master cylenders. Last time the car was serviced, one of the wheel cylenders was replaced which resulted in the brake fluid being replaced with standard stuff. The master cylender is now looking darker than the clutch cylender and has some crystle-like deposits on it. Time to put silicone fluid back in, I think! It's advertised, along with all its advantages, in one of our club mags, but a specialist classic car parts catalogue reccomends against it's use. Anyone know anything about it?

[DAVID PATERSON]

I use it in my race car, it has a number of advantages, it is less inclined to mix with water and it has a higher boiling point, but it must NEVER be mixed with regular mineral brake fluid. They are NOT compatible. Also, silicon brake fluid is frighteningly expensive, in Australia it is 10 times dearer.

[Bluebottle]

I was already aware of the incompatability, the system will need to be fully drained before I go back to silicone. It is more expensive, but it dosn't need to be replaced as often. The catalogue which recomended against it's use claimed it was more likely to absorb water- a nice bit of misinformation I think!

[Airhead]

I always thought the two advantages David mentioned above were the reasons for using the synthetic product. Having said that why bother in a road car?

[enzo]

Silicone fluid WILL absorbe moisture much faster than regular fluid! For that fact alone, no one in their right mind will use it in top level race cars.

If you are really concernd about heat, stick with Castrol SRF or AP 550 or 600. If heat truely isn't THAT big a problem, stick with Castrol LMA or Pyroil.

[Chris Y]

Well, this is getting pretty damn confusing here, so I'm going to find out some facts.. I've just done a brief web-trawl, and found this snippet of info, regarding silicon:

The makers of the rubber pieces that are used in brake systems recommend that if DOT5(silicone) fluid is used then all parts should be new and the system should be flushed with solvent to remove all traces of glycol based brake fluid. The reasoning is that the DOT5 stuff is non-absorbent of moisture and the DOT 4, 3 etc. is. The mixing of the glycol and silicone in the system will allow moisture absorption of glycol to get moisture mixed with the silicone and this is not good. This leads to a high viscous sludge according to someone I know that did this to a classic car.

This was in a discussion about ABS systems. It seems to point out that pure silicon fluid doesn't absorb moisture.

[Chris Y]

It also says [about DOT 5]:

If you actually get the details on this stuff it is not really intended for active vehicles but is rather for race cars which will see high temps for extended periods and for classics which aren't used much and are big targets for moisture corrosion. Classics and race cars will have most of their systems installed as new parts.

[Bluebottle]

It's interesting that Enzo says silicone does absorb moisture and then goes on to reccomend Castrol- the catalogue I have reccomending against silicone does so by quoting Castrol- who don't make the stuff!
The Hurricane does less than 3000 miles each year so qualifys as a big target for moisture corrosion. The Hurricane will get it's silicone back after a clean-out. Anyone know why the aly cylender has gone dark with the Dot4?

[DAVID PATERSON]

I use Castrol SRF, I'm sure that stands for Silicone Racing Fluid.

[strad]

In a road car there is abso;utely no need to pay the money for silicone. I does absorb more water.
Use a high quality normal fluid.
Changing your fluid is your best insurance against corrosion.