01-02-2020, 01:43 AM | #1 |
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M240i stock brake fluid vs track worthy fluid
Can someone give me some insight into what the difference is between the m240i oem brake fluid and that of something I'd want to use for track/auto cross course? I've read conflicting info on this. Some say the fluid's rating is same as what it would be swapped with and others say what you swap with is better for track use. Un-confuse me please! Lol.
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01-02-2020, 08:51 AM | #2 |
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The primary difference is the ability to withstand the higher temperatures that your brake fluid will experience due to the extra heat transfer you see from the more extreme braking activity on a track.
The most noticeable thing you may experience with the OEM fluid is the brakes getting spongy, which in turn significantly reduces that ability of your brakes to perform at their best when needed. Going out for the first time you are likely fine with the OEM fluid, but if this is something you continue with you would definitely want to go to a high temp fluid (I'm a Motul fan myself).
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01-02-2020, 08:56 AM | #3 | |
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01-02-2020, 09:33 AM | #4 | |
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If I was shopping off that list, I'd choose the Motul 660. As it is, I use a fresh fill of Castrol SRF before each track event. If I was having trouble with brake fluid boiling, I'd switch to AP Racing's Radi-Cal R4: https://www.essexparts.com/ap-radi-cal-r4-brake-fluid. This is a much more comprehensive brake fluid comparison list: https://www.lelandwest.com/brake-flu...ison-chart.cfm.
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01-02-2020, 02:33 PM | #5 |
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You'll want to Google search "dry vs wet boiling point for brake fluid" and then realize your stock fluid has different dry and wet boiling points than competition fluid. Once the fluid boils, you introduce gas into the system, and that is why the brake pedal gets the spongy feel and the brakes can fail to stop the car. First-timers on track are especially in need of high-performance fluid because they tend to have poor braking technique and overheat them quickly. I use Motul RBF 660 for track and have no boiling issues. I buy it from Amazon...
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01-02-2020, 03:38 PM | #6 | |
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With stability control enabled, poor throttle technique can help to use up rear brakes faster than would otherwise be the case. With our cars, you know you're overusing the brakes when the blue calipers begin to change color.
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01-07-2020, 02:54 PM | #7 |
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01-07-2020, 03:14 PM | #8 |
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01-07-2020, 03:40 PM | #9 |
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Reminder- if you go with a more aggressive brake fluid, understand it will absorb water at a faster rate. So chance it more frequently than the 2 years your car computer will call for
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01-07-2020, 04:44 PM | #10 | |
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Plenty of pics around. Mine are still blue - ask me how.
The second photo in the post by Moflow is how they can end up. It's a very unattractive green-brown color. Quote:
One way around it is to use Castrol SRF, which has a much higher wet boiling point than the typical fluid. The reason for this is that it's hydrophobic (i.e., it doesn't absorb water). This is a comparison list of over one-hundred fluids that are in the marketplace, along with their boiling and other data points: https://www.lelandwest.com/brake-flu...ison-chart.cfm. This is Bimmerworld's page for SRF; it has an explanation of why you might choose the fluid: https://www.bimmerworld.com/Brakes/B...ake-Fluid.html. Most people are put off by the price. I've found it to be a good track fluid, and I have my braking system flushed with SRF before each event.
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2017 M240i: 23.6K, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
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01-08-2020, 12:08 PM | #12 |
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I'm lazy and don't like to bleed my brakes every HPDE event so I use SRF. SRF lasts me about 10mo.
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01-09-2020, 07:11 AM | #13 |
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More specific to this issue is that the track brake fluid (Motul etc) is not low-viscosity, so if you get winter temps down near freezing you will want to swap for factory fluid each winter - the track fluid won't work right in the ABS when real cold, and the low vis isn't real good at track temps (apparently tolerates them, as per the boilpoint specs, but not optimal). You need to use a place that can run the computer ISTAR sequence, since conventional flush won't get the fluid out of those passages (some of the handheld diagnostic units can do this, but pricey). The SRF is a different chemistry, and it may qualify as low-vis - can't say for sure. FWIW, my dealership was happy to replace pads/rotors under warranty despite them having been burned to a crisp on track, and with the system full of Motul, so I stopped worrying that this would be a warranty problem; your place may take a different view.
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01-09-2020, 09:35 AM | #14 |
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My dealership suggested and used Motul RBF600 when they installed my wagon BBK, would agree it's nothing to worry about from a warranty perspective.
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01-09-2020, 09:46 PM | #15 |
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General question, are there are any drawbacks to using track/autocross types of fluid vs. BMW fluid for a daily driver that will never see a track, other than cost? I've heard that track pads suck for street use, but nothing on fluid.
Was thinking of flushing with ATE TYP 200 or RBF600. |
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01-09-2020, 10:20 PM | #16 |
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Most are more expensive.
Some pick up moisture quicker and therefore need to be changed more frequently. (ATE TYP 200 lasts pretty long, though). Some are a bit more viscous and don’t work as well with the ABS system. |
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01-10-2020, 04:54 AM | #17 | |
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While regular fluid may last up to 3 years |
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01-11-2020, 06:11 PM | #18 | |
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None of the high-temp/track fluids are remotely low-viscosity at the standard test -40C temp. Castrol SRF is listed at 1300-1500 mm2/sec. (Compared to 2.5-3.5 at 100C.) Motul RBF600 is 1750 at -40C. Plain DOT 4 fluids, like ATE SL are also around 1400. So, the Castrol SRF isn't any worse than a standard fluid. I can't find a reference for the BMW brake fluid, but the Pentosin LV I use in the winter is listed at <700. ATE SL.6 low-vis is also a max of 700. Less than half of any of the standard or track fluids. If fluid that is half as thick will cycle my ABS faster and more precisely, that's what I want in the winter. I swap my summer track fluid for low-viscosity in the fall. And back to track fluid in the spring. Usually when I swap the winter tires on/off. Kind of a pain, but worth my peace of mind. And I'm definitely sure I don't have old water-saturated track fluid that way also. And I'm getting really good with my pressure-bleeder and the ABS cycling process. |
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01-11-2020, 10:41 PM | #19 |
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01-18-2020, 03:00 PM | #20 |
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I have a Schwaben/Foxwell scan tool (14020SCH) that can do the ABS bleed/flush cycle. I also have the BMW ISTA diagnostic tools on a laptop that connects with an OBD/Ethernet cable.
The Schwaben scanner is less cumbersome, but it can be a bit cryptic to use. The ISTA tools have a lot more explanatory text/pictures, but juggling the laptop and cables is kind of a pain. (Not to mention the hassle of finding/installing/debugging the not really legal ISTA software.) One of the reasons I went the ISTA route is that I thought I was having an issue with the scan tool software when I was I chasing some air in the brake system. Turns out the scan tool was working perfectly. The directions the scan tool kept saying 'left side', and it would never do the right side calipers. Well, it turns out there is no right side flush in the BMW process. The ISTA tools do a better job of explaining that you only need to do the 'front' and 'rear' circuits from the left side calipers. Guess they assume you're usually working from that side of the car. I only do the full ABS cycle when I'm putting the LV fluid in. You use a lot of fluid when doing the ABS cycle. An extra 1/2 quart or so, depending on how quick you work and how far you crack the bleeders open when you're running the cycle and doing the pedal pumps. SRF is way too pricey to just pump it through and waste it. And it's really the ABS block where the LV fluid is necessary anyway. I also figure that internal fluid in the ABS side of the brakes doesn't really see the heat that the calipers do, so SRF isn't really necessary. I make sure to suck out all of the fluid in the reservoir before putting the SRF in to minimize mixing in the lines when I flush. BMW doesn't make it easy to do this with the level float in the way. I use some narrow tubing and carefully snake it down into the bottom of the reservoir, and then suck the old fluid out with a large syringe. |
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01-19-2020, 12:46 AM | #21 | |
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01-19-2020, 10:24 AM | #22 |
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Thanks for the input, I'd considered those Schwaben's but wasn't sure they would do the trick. Am I getting it right that for the summer installation of the SRF you don't run the ABS-flush and just leave the LV fluid in the ABS unit?
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