Apex996

My shop screwed up and topped off my Endless brake fluid with Castrol SRF. (less than 2 oz.)
I know Castrol is not to be mixed with anything else.
After consulting the Castrol website I see that it now says mixing is possible but not preferred. Do I need to worry about this at all?

• It is miscible with all conventional fluids meeting the US Federal Standards FMVSS 116 DOT 3, DOT 4 and DOT 5.1, ISO 4925 and current SAE J1703. This means that changing the brake system to Castrol SRF is easy. Drain and flush out the conventional brake fluid with Castrol SRF then top up the system with Castrol React SRF Racing. Although Castrol React SRF Racing is miscible with conventional brake fluids, topping up Castrol React SRF Racing with conventional brake fluids will reduce the benefits of the product.

ProCoach

lmnsblu355

I think you should be fine. Endless fluid has a lower wet boiling point than than SRF. They are both DOT 4. Why would SRF degrade performance of the Endless?

If you had SRF in already, then topping off with something else would degrade the performance of the SRF but you are in the opposite situation.

But if you want the best protection, flush the entire system with SRF.

okie981

I run Endless in my BS based on recommendation from the GT car tech at my preferred local Porsche dealer. I did quite a bit of interweb research a few weeks ago when I thought another indy shop had mixed Motul 660 with my Endless. Turns out they hadn't but I wasn't sure for a few days. Research bottom line, SRF and Endless will mix OK and not cause any dangerous situations, but you should always aim to have the same brand/type of fluid throughout your brake system. If it were my car, I would pick the fluid I want to use and flush it all the way through. During that research I did, the only downside I found with Endless is that it is slightly to the acidic side of pH balance, and it has several upsides. Flushing my system as often as I do, I'm not concerned about the pH balance of Endless. SRF is great stuff too.

Apex996

Thanks for the reply okie. Your findings support my own. This is not as dire a situation as I was led to believe. Someone suggested there was some serious chemical incompatibility which would require a complete flush.
I also change fluid enough that I'm not concerned. I run enough Endless through my brake system that the SRF will be flushed out soon enough anyway.

ExMB

Here is one tidbit that may or may not be related to your situation.

My clutch uses the same brake fluid reservoir. When I had the shop switch to SRF they forgot to do the clutch which had the OEM fluid. Needless to say that clutch fluid boiled on track.

thebishman

TXE36

Did that cause a problem with the brakes? I can't imagine the clutch fluid between the shared reservoir, clutch master, and clutch slave getting hot enough to boil even under the worst of circumstances.

Are you blaming residual non-SRF fluid in the clutch system for causing boiled fluid in the brakes?

Just curious. My clutch also shares fluid with the brakes and I never bleed it.

-Mike

ProCoach

bgiere

Endless will mix with SRF. 2 oz. is not going to move the needle on wet/dry boiling point. No worries. BTW, Endless RF 650 is good stuff.

okie981

Yes. But in the OP's case, SRF and Endless would not be much concern performance-wise. Lots of other DOT 4 fluids could be more to be concerned about.

okie981

Yep, Endless RF650 is indeed good stuff.

thebishman

ExMB

No, what I'm saying that my clutch fluid boiled. That is in a mid engine car where there is a slave cylinder for the clutch. You will have a lot of residual heat in the engine bay after coming off track. The engine exhaust fan management is responsible for evacuation of the heat. Depending on time between runs one could experience an issue with the clutch. In my case as long as I had 1 1/2 hr between my run groups everything was fine. How I found my issue was that I tried to take out a student 1/2 hr after I came off track. The smell was very evident while sitting on grid waiting to be called out on track.

Stuttgart

I don't think anyone has mentioned that these are 2 different chemicals... Castrol SRF is silicone based, while every other conventional brake fluid is glycol ethylene. Depending on how big your reservoir is would get a turkey baster and just suck most of the fluid out, then replace and bleed.