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понедељак, 17. јануар 2011.

Brake Fluids (kočione tečnosti na engleskom)

There are currently four current standards (with some variations) or at least species (class, categories, ...) of brake fluids:

DOT 3, DOT 4, DOT 5 and DOT 5.1

A special group is DOT 5, which is based on silicon oils and has the highest standard value (quality), although difference compared to 5.1 a very small and in practice negligible. DOT 5 oil WOULD NOT BE mixed with other types of fluids. This type is rarely used, commonly at the American automakers and the motorcycle.

Other groups: 3, 4 and 5.1. may be mixed with each other. These oils are based on glicolethers and polyglycols. 5.1 have in themselves and some of borate esters (and still is the based as 3 and 4) with better overall performance and it is likely (possible) that future standards ("DOT 5.2 or 6") will be based more on them, borates. However miscibility is guaranteed, but should take into account that adding lower standard and higher quality degrades to do only in emergencies (although up to 10% will not bother you).

Of course it is better top-up liquid with higher category but one higher is the best, again. And of course if some of the oil left you, the same is the best.

Take care that the oil (as hygroscopic) would be tightly closed.

I must mention here that the DOT 3 (or 4) fluids based on mineral oil not be mixed with other fluids. Although this is more a matter of history it is important to be noted. Braking systems based on mineral demanding such oils. Polyglycolic / glicolethers oils can not meet the requirements that such systems require. Of course even bigger problem is that these two types of fluid do not mix and they are completely incompatible.

Mineral oils, brake fluids, are survived in Citroen's vehicle within the standard CITROEN B 712710. It is a LHM fluid. In LHM acronym guessed that the L for the liquid, H and M for hydraulique and mineral. Otherwise, they are used for hydraulic in Citroen vehicles.


The higher DOT number, higher the quality is, due to higher requirements. Although top (good one) DOT 4 can reach DOT 5.1 (at least in some domains) remains that you will get through cheaper and better with the 'small' name and the larger DOT’s.

"True professionals" at all the hydraulic oil (including brake fluids) looks like ’piece of cake’ (and everything is almost same) that they were targeting a similar composition and that there are very few additive ('ordinary hydraulics’ – „base oil (oils) and a few % of additives, it does not matter who is the producer, more important is the price (at least not to be peppery high)").

However, between the better and the average, there are differences. Naturally better are not reasonably expensive.

The most important thing is that these oils are very hygroscopic (Absorbs moisture) and are rapidly degraded because of this. They build up an average of up 1 to 4% moisture per year and max. 5% or recommended 3% raise for 2-3 years or less.

The specification tables have data for the temperature of boiling point of dry and wet (3% of water). How big differences are easily noticeable, it could be concluded:

Much more significant is (that) the brake fluid changed regularly (at two years), the medium class will certainly be a better than top class B.F. that changes on three years.

The difference from the original oil (without water or trace of it) and one with 3% water would be up to 100cel. degrees.

Fluid changes even with 2-5% water. Top class B.F. with 1% or 0.5% often can not be compared with the mediocre but "dry".

If you are not complaining about money, change your oil for a year and you will have (on average) the best brake fluid in Europe, World, and the Solar System if you use any that meets specifications.

Although at first glance looks fascinating, if for example a DOT 4 fluid has a dry boiling point of 280cel. and look for class better than the one that has 265cel. in practice, fastly become the same, and although it worth some money certainly not more than 10-15% of the price.

Course the ’hands’ (work in service) cost but what else to do. If you have ABS entrust your oil change to the service (good mechanics who knows to do it).

DOT 4 and DOT 5 are less hygroscopic oil and can withstand more than two years (or as recommended by producers), even up to 4 but it is better to change in the max. 3 years.

An exception in terms of mixing is the mineral brake oils but they are rarely used (for years). Only Citroen has used these and it does not mixable with the other.

It is important to note that 3, 4 and 5.1 oils are SOLUBLE in WATER! In polar solvents (e.g. alcohols), of course.

These oils are aggressive on paint and can damage parts of the car though this feature is a bit overvalued. Of course DO NOT leave oil on painted parts of the car (in general metal) because these oils are polar and have (relatively) high pH value (the alkali) and their feature (nature) is, that they are mild solvents. Aggression decreased in the rise of standards so the most alkaline fluid is DOT 3 (pH 10). Although it is not 100% right. So remove them with a cloth or paper, but do not panic, it will not just eat the paint in minutes (I count that it may drop primarily in the engine compartment) but as soon as you remove the less damage would be.

Their viscosity at higher temperatures similar (3, 4 and 5.1) and at the low temperatures 5.1 has significantly lower viscosity and the DOT 4 slightly less than DOT 3 .

And finally: whether to use 'higher DOT' than recommended?

Although in the most cases it is possible, do not at any price. Depends from vehicle to vehicle. A slightly different viscosity does not affect too much on the braking system but it is possible that there are such cases. More importantly, the behavior of the seals, as the fluids are quite similar to the effect that there is not much influence (and essentially not) but because of slightly different composition additives and borate ester in 5.1 a bit of caution is advisably.

DOT 4 where the DOT 3 (synthetic) is recommended may be O.K. in 99%. Besides 5.1 is not as superior to 4 in order to pay off, especially when the manufacturer does not mention (underlined) it.

Although the most important of all mentioned above:

It is better to regularly change the oil (fluid) than go to higher standards and more expensive brands.

DOT 3 max. on 2 years (or less), DOT 4 just in 2 years (or max. 3) and DOT 5.1 in 2 to 4 years.

Of course, use brake fluids of leading manufacturers. More importantly (perhaps more then elsewhere) that the product would be original one. These two things assure fulfillment of standards what is the most important in this story.

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