Castrol SRF brake fluid

[Iansparky]

I am about to do a complete overhaul of my series 1 brake system, new Zeus calipers front and back, new master cylinder and servo, new hoses and potentially brake lines.
My opinion on using silicone brake fluid keeps swinging back and forth with each post I read. I have however found a castrol racing fluid called react SRF, its apparently based on silicone esters, it doesn't damage paint it is only mildly hydroscopic, much less so than Dot 4, but does absorb some moisture, this would prevent the problem from water pooling as it apparently can in a fully silicone fluid.
Castrol recommends fluid changes for racing every 18 months so in a road car I think this could be doubled, it is very expensive (£60 per litre) but if we accept that full silicone fluid needs changing anyway to avoid water pooling then it seems to make sense to me.
Has anybody any experience of using this fluid

[mgcjag]

Uh the old silicon debate....iv used dot 5 silicone for years with no issues of water pooling.....as far as im aware most of the restoration companies use it..just look at the colour in the reservoir on many of their restorations..light purple....also there isn't a problem with dot 4 if used correctly..wash splashes off with water and dont use diy pressure bleeders you could end up with it everywhere....the Castrol you mention is still dot 4 yes it will work in a road car...is it necessary?...Steve ps the reccomemdation for change is 18months...why do you think this can be stretched to 3 years....

[Iansparky]

The 18 month change recommendation is for racing so as to maintain the ultra high wet boiling point, I just figured that as we wouldn't need such high figures the change interval could be extended. I also have had silicone fluid in my spitfire for the last 15 years with no problems and have not touched it. Maybe I am over thinking things, it's hard when there are so many conflicting opinions.
Ian

[mgcjag]

15 years is too long to keep dot 5 without replaceing it...the one I use is change interval 8 years although I bleed some off more regular just to ensure no water in it...Steve

[paydase]

Steve,
If there would be no water ingress, do you think that the Dot 4 efficiency could remain for 10 or even 20 years?

[mgcjag]

Hi Serge....I'm no chemist....I follow manufacturers recommendations....we don't have sealed systems...Steve ps...the shelf life of an unopened bottle will give the answer

[rfs1957]

I sat on the fence for decades over The Silicon Issue.

Having seen how nasty my rear calipers were after 10 years usage, including regular bleeds, after the recent total rebuild I decided to find out for myself and went for Silicon - which I used at all stages of assembly too, to be 100pc consistent.

I couldn’t face the frilly paint that virtually every car carries somewhere in its depths below the master cylinder area.

It’s only been a year, and 4.000km, but the use of this stuff has been completely glitch and incident free, and my brakes and clutch have never worked better.

Automec brand, Dot 5.

Sample of one, but so far very happy with my Purple Bottles.

[1954Etype]

Used it for years with no issues - ever. Important to note that you should only use it with a new system. People seem to have had trouble when DOT4 has been in the system previously.

[MarekH]

A good way to encourage reliability and longevity is to boil out the dissolved impurities from the brake fluid. Obviously I don't think the kitchen sink is the appropriate way to go here, but as all of the lenses I make are done using a process under vacuum, I have access to all of the pro-grade equipment. Putting the bottle of brake fluid in the vacuum chamber for ten minutes prior to bleeding is an easy thing to do.

Liquids boil at a lower temperature when they are at lower pressure, so what happens is all of the dissolved gases and water sitting in the fluid boil off even at room temperature when the liquid is put under vacuum. The resulting brake fluid is cold to the touch, as boiling off the impurities uses energy and latent heat of vaporisation is extracted from the brake fluid itself.

If it isn't colder to the touch, then it didn't have much or any dissolved impurities that needed extracting. If it's colder when you pull it out you know it boiled off some dissolved water or air.

If you are near Guildford and arrive in an etype, feel free to take advantage.

kind regards
Marek

[Gfhug]

If changing to silicone fluid, besides changing seals in the master and slaves and servo, do you recommend replacing all flexible hoses too? Thanks for any comments.

Geoff

[paydase]

A maybe silly question.
When converting to silicon DOT 5 for brakes, is it worth putting also DOT 5 in the clutch fluid bottle or would it be a fatal mistake?

[mgcjag]

Iv used dot5 for both brakes and clutch......there is lots of discussion on its use.....some have said that it has damaged seals in cylinders etc.......I havent found this to happen and have just replaced dot 4 with dot5 and flushed it through......your choice though.......dot 5 spec is that it can be used mixed with other fluids as it was developed for military use.....I have also rebuilt brakes and clutch systems with all new components and used dot5 with no issues....Steve

[Gfhug]

Thanks Steve, as parts are off the car the seals may as well be replaced as it’ll give me a chance to check the bores. But will trust the flexible lines as they shouldn’t cause any sticking of pistons.

Geoff

[paydase]

Thank you Steve.
Good to know.

[PierreW]

Just my experience with DOT 5 silicone brake fluid: I put silicone in my MGA over 40 years ago (1983) and I haven't changed the fluid, bled the system, had any leaks or blockages since... so I didn't hesitate to put it in the MK2 in 2020; the E-Type and Lotus will follow if needed.