my british land rover always used dot 4 fluid because of the natural rubber compounds in the clutch and brake components.
A few years ago I started using Dot 5 synthetic fluid.
Now I notice a plethora of ''synthetic dot 3, dot 4, dot 5 … wtf?
what’s happening here? is this a sales gimmick? I still figure synthetic is synthetic… what’s with the dot3,4 and 5 synthetic?
Not answering your question, but related … If synthetic he really means made from petrochemicals (think polyester, rayon, etc.), what the hell is synthetic oil?
It’s a bit murky but synthetic oils are usually refined from better base feedstock and lower-refined products like mineral oil can (but are not always) be replaced by silicone or non-petroleum hydrocarbon products like glycerin variants.
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the real drive of my question is why have dot 3,4, and 5 since 5 is/was originally synthetic.
my argument is labeling the cat 3 or 4 is redundant i should think. this is why I questioned it as being just a sales ploy.
DOT 5 is silicone based and incompatible with DOT 3, 4, and 5.1 which are all glycol-ether based.
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DOT 5 is a totally different silicone based fluid. You have to clean all the old stuff out. It is prone to trapped air, if you shake the bottle up air bubbles take FOREVER to migrate to the top and dissipate.
FYI - If you are looking for high temperature performance, Ford makes a DOT 4 that works very well. One of their cars had the brake line too close to the exhaust, so instead of redesigning the car they came out with this fluid. I can’t recall the part number offhand,
I had no idea DOT 5.1 got invented, you learn something new every day.
welllllllllllllllll, I read ALL of what has been presented here (many thanks) but my question as to why they make a synthetic dot 3 and a synthetic dot 4 and how it can be different than dot 5 (excluding dot 5.1) has not been addressed, and neither in the article.
I may go back to using dot 4 but I wonder anymore if the british even use the more expensive natural rubber in their cars anymore? they may be going the way of tires and air hoses where some sort of plastic is more prevalent.
DOT 5 is a silicone based fluid that behaves quite differently than the others and does not mix with them. For one thing you will have spongy brakes with 5, it never gives as firm a pedal as the others. A “synthetic” 3 or 4 or 5.1 presumably can mix with those and behaves in a similar manner.
The raw materials for both synthetic and conventional DOT 3 & 4 & 5.1 braking fluids are the same in principle. Polyethylene glycol is included in all of them.
Synthetic brake fluids, in theory, are superior to their traditional counterparts, because their molecules are made more consistently by synthesizing the base stock, leading to more homogeneous molecular mass distribution and increased cross-batch consistency etc.
Whether this difference is worth a significant price uptick is questionable. If your brake system is certified for DOT 4, you may happily continue using conventional DOT 4. Manufacturers may put more energy into fine-tuning their synthetic formulations, and may, just may, mix in better anti-corrosion additives etc. than into their conventional products. However, a car that has been going well on conventional brake fluid will not miraculously last longer (or brake harder) if you switch to synthetic.
DOT 5 ist the only exception to the above, being based on silicones, as previously stated by others. Thus, for the DOT-nomenclature it was a bit unfortunate, that DOT 5 did not universally replace DOT 3/4, necessitating the DOT 5.1 to continue the glycole family of brake fluids…
The high temperature resistence increases from 3 to 4 to 5.1; viscosity of 5.1 is lower, improving time-critical load-changes in ABS- and ESP-systems. However, a valid reason to stay with DOT 3 for vintage cars or older motorbikes may be incompatibility of the sealings or lines with the newer fluids*. For braking action alone, downward compatability is declared.
*: It is a bit like the potential problem with synthetic maritime diesel (GTL) which may damage the o-rings and sealings of older yachting marine engines.
“bob the oil guy” may of come close with a differentation but claims Dot3 regular and dot 3 synthetic are ‘‘both synthetic’’ … in any case, i think i’ll give up on this. btw, I read everything everybody posted. I believe the ghist of my question didn’t quite gain traction.
It may be that I do ‘get it’ but having at least once replaced all the rubber in my old series 3 Land Rover I am very observant about british natural rubber compounds.
The musings may become moot soon: Many key brands no longer offer non-synthetic brake fluids at all in western countries. It may not be worth it for them to keep dual production lines. (For example, Castrol offers three different performance/marketing grades of DOT 4, all of them synthetic…
yea, probably have to be a chemist. remember, as licensed engineers we’re hired as ‘‘operators’’, not repairmen !!! i’m sure all of us forget that by necessity?
The primary reason to use 5 is usually that it is easier on rubber parts than any of the others, which if your car has bits not easily sourced, makes up for the PITA involved in using it.