In the good old days, brake fluid (DOT and DOT 2) was a castor oil-based fluid that was use for lubrication as well as for actuation. These days, most brake fluids are glycol-ether based fluids. The exception is DOT 5 which is a silicone-based fluid.

DOT 4 Plus FEBI BILSTEIN, SWAG Brake fluid cheap AUTODOC DOT 4 Plus FEBI BILSTEIN, SWAG Brake fluid cheap AUTODOC

now here is the fun part, DOT 5.1 is pretty much the same as 3,4 and 4+ all glycol based where the straight 5 is a silicone. Obviously I don't want to be mixing fluids wrongly but I also don't want to go replacing the brake system unnecesarily either !However mixing for example Glycol DOT3 with Glycol DOT4 would give unpredictable performance. Nowhere have I seen anything saying "this is ok". I suspect the reason is that a mixture of formulations may give an unproven boiling temperature.

FOSSER Brake Fluid DOT 4 Plus – Fosser FOSSER Brake Fluid DOT 4 Plus – Fosser

Valvoline used to have a great Dot 4 for cheap (their Synpower brake fluid) but it has been replaced with a good DOT4 which is now even less expensive. Generally this is a bad idea, but the main thing warned against is mixing Silicone based fluid with Glycol. This thranslates to not mixing DOT 5 with any other DOT standard fluid. For those that have become hopelessly lost, the short version is this; for the purpose of replacement fluid in our W211s, glycol based DOT 5 .1 and Dot4+ are essentially the same thing. One or the other is bound to be available in your local parts store. Just don't use silicone based DOT 5 (point nothing). That's specialty stuff for non-ABS systems, and doesn't play nice with glycol. However what you just said “glycol based DOT 5.1 and DOT4+ are essentially the same thing” is not true technically or otherwise. Brake fluids labelled DOT5.1 comply to a standard, while the brake fluids marketed DOT4+ or DOT4 PLUS are just that: better than DOT4. So, essentially they are not the same. That means those W211 owners who can't find Dot4 Plus (orDot4+) on the shelf at their local parts store, it's perfectly acceptable to buy the bottle that says Dot 5.1

j_cd wrote:I'm not sure which year Volvo switched from DOT 3 to DOT 4(+). The '98 manual says DOT 4+. My guess is, the Volvo engineers liked that DOT4+ fluid, but it didn't really catch on, and our brakes are fine with regular.

DOT 4 Plus Brake Fluid | Bob Is The Oil Guy DOT 4 Plus Brake Fluid | Bob Is The Oil Guy

The Mobil Brake Fluid DOT 4 is suitable for all disc, drum and anti-skid braking systems used in average to high performance vehicles requiring DOT 3 or DOT 4 level performance. Features & Benefits: Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine. by Krons» 17 Jul 2022, 19:03» in V70, S60, V70-XC and XC-70 Cross Country 2001-2007 8 Replies 780 Views Last post by Krons

How to Add Mercedes-Benz Brake Fluid

DOT 5 is a silicone-based fluid and is separate from the series of DOT 2, 3, 4, 5.1. It is immiscible with water, and with other brake fluids, and must not be mixed with them. Systems can change fluid only after a complete system changeover, such as a total restoration.